Problamatic Insects


Problamatic Insects

PESTY INSECTS

Quick Tip! Whenever you spray plants with anything, make sure to get the undersides of the leaves too, as this is where many pests like to hang out! A one-hand pressure sprayer / mister is also really helpful for spraying leaves. 


We found most of the information listed below through the Colorado State Universitys research program.  https://hempinsects.agsci.colostate.edu/hemp-insects-text/.  As we are growing in Texas for the first year, we will update this list continually for any other insects that may effect hemp specifically in Texas.


  Insects that Chew on Leaves  

Caterpillars and worms eat holes in leaves and leave droppings that look like black specks.

Beet Webworm 

The beet webworm (Loxostege sticticalis) is a caterpillar that reaches moderately large size when full grown (¾ inch). It is generally green marked with striping and white spots that have a black center. The caterpillars will typically be found feeding amongst emerging leaves and around buds, usually within some loose silken webbing that produces a shelter for the insect. Adults emerge in June and lay eggs, typically in a small cluster on the leaf underside. Upon egg hatch, the larvae move to feed on the plant. First stage larvae feed on the leaf surface, producing minor skeletonizing. Later stages, will cause more generalized leaf chewing and produce the visible webbing. Adults emerge in about a two weeks and produce a second generation. From July into September all stages of beet webworm may be present as generations overlap. Damage to hemp by this insect is likely to be minimal and insignificant. Other plants are more favored hosts, notably several common weeds such as lambsquarters, pigweed and Russianthistle. The small amounts of leaf chewing beet webworm does produce on hemp can be expected to be fully tolerated by the plants. Numerous natural enemies that may feed on beet webworm are also common in most hemp fields.


Beet Armyworm

The beet armyworm (Spodoptera exigua) is a caterpillar that feeds on leaves and developing flowers/fruits/seeds of a great many plants. As it does not have a way to survive outdoors in climates with cold winters, it periodically dies out in much of North America. Annually it will disperse northward during summer months and can be expected to occur on cannabis in highest populations late in the season. As with the corn earworm, larvae of beet armyworm that are carried on harvested plants will continue to feed and develop as plants dry. Damage to hemp by beet armyworm to hemp is likely to be minor, as outbreaks are dependent on southern migrants and the feeding injuries caterpillars produce are dispersed throughout the plant, much on leaves rather than flowers and seeds. Problems may occur when beet armyworm populations are high late in the growing season and they move into maturing buds and seeds.


Cotton Square Borer/Gray Hairstreak

The larvae of cotton square borer (Strymon melinus) are pale green (sometimes brownish), fuzzy caterpillars that may reach about ½-inch length when fully grown. Adults are attractive butterflies, with an overall blue-gray coloration, and small thread-like “tails” extending from the hindwing. The adult is also known as the gray hairstreak. Winter is passed in the pupal stage, and adults may be first seen in late spring. Females lay single eggs (not in a mass) on leaves and eggs typically hatch in 4-6 days. Young larvae feed on the leaf surface; later stage larvae may tunnel into stems, leaf midribs and, perhaps, buds. When full-grown, about 3- 4 weeks after egg hatch, the larvae then pupate, attaching themselves to the plant with a small bit of silk. A week or two later adults emerge to repeat the cycle and there are probably two, perhaps three, generations completed annually. This is an uncommon species in hemp. Feeding injury to leaves is minimal and insignificant. Some bud tunneling may occur, although it has not yet been documented to occur in hemp.


Earwigs

The European earwig (Forficula auricularia) is the only species of earwig found in much of the northern US. A non-native insect that was accidentally introduced to North America, and is common in gardens and greenhouses. The European earwig is a true omnivore. It feeds on plant matter, particularly leaves and flowers, which sometimes produces significant damage in gardens. It will also feed on insects, making them a very important predator of aphids, insect eggs, and small soft-bodied insects such as caterpillars. It is a night active insect, which hides in tight, dark, moist sites during the day. European earwigs spend winter in the adult stage, hidden under plant debris, mulch or other sheltered sites on the ground. In late winter the female will produce her first clutch of eggs, which are laid in a cavity in the soil. The mother remains with the eggs until they hatch and will continue to guard them until they have molted again. These immature stages then disperse to feed and develop on their own. The female may then produce another clutch of eggs that will hatch in mid-late spring. Immature stages generally resemble the adults, but are smaller, paler and have less developed cerci (pincers) on the hind end. They become full grown within a couple of months after eggs hatch, with rate of development mostly determined by temperature. The prominent cerci of this insect often attract attention and concern, but they are not able to produce any noticeable pinch. (Earwigs do have jaws that can produce a slight pinching sensation.) The shape of these cerci can be used to differentiate sexes, with males having bowed cerci and females cerci that are straight. European earwig does possess a pair of wings that are normally folded and covered by a pair of short wing covers. However, European earwig cannot fly. European earwigs produces minor leaf injuries that would rarely attract attention. Significant infestations are unlikely in production fields, but populations may develop well in and around greenhouses where there are live plants and abundant areas of sheltering cover produced by pots, flats of plants, and other materials or debris on the soil surface.


Flea Beetles

Flea beetles are tiny beetles that have enlarged hind legs that allow them to jump. Damage is produced by the adult beetles, which chew on leaves. Leaf injuries initially produced are small pits produced by chewing, but as leaves develop the injured areas usually form holes (“shotholes”) in the interior of the leaf.  Adults may be expected to be seen in hemp early in the season (June, early July) then again in late August and September. The adults have a very wide host range but develops in the highest numbers in the mustard family plants, canola, cabbage, broccoli, and many common weeds, such as flixweed. There are also a very large number of crops on which the adults will feed, including lettuce, beans, potatoes, and sunflowers. The larvae of flea beetles develop by feeding on the roots of plants. However, the injury that the larva produces is generally considered to be negligible to the plant growth. Adult feeding also is usually insignificant to well established plants, although high numbers of flea beetles present on seedlings can retard growth and even kill plants.

The western black flea beetle is the smaller of the two, about 1/10-inch long, with a shiny dark body. The palestriped flea beetle is a bit larger, about 1/6-inch long, and marked with yellowish stripes along the back. The hop flea beetle (Psylloides punctulata), occurs in more northern areas and is reported to be a potentially serious pest of hemp during early growth stages. The larva of the flea beetles may also damage the crop by feeding on roots.  There is a high potential for these insects to significantly damage hemp when large numbers of these beetles coincide with seedling stages. On such young plants the injuries produced by many flea beetles could cause significant affect to plant growth (including damage to the growing point) and conceivably could even kill some plants. These injuries on established plants with a larger leaf area would be expected to cause negligible/insignificant crop injury.


Grasshoppers

These seemingly harmless garden creatures will happily eat your cannabis leaves, and possibly your entire plant! There are well over 120 species of grasshoppers that occur in the western states. Grasshoppers damage hemp by chewing on leaves and by gnawing on stems. Hemp has good ability to tolerate leaf loss, and will tolerate low-moderate levels of grasshopper defoliation on established plants. Grasshopper feeding sometimes may destroy the growing point of a smaller plant. Hemp is most susceptible to leaf loss by grasshoppers when plants are very small.  This is when leaf chewing injuries may significantly retard growth and even kill some plants in extreme situations. More serious damage results when grasshoppers gnaw on stems. This habit occurs most commonly with the two largest species of grasshoppers that occur in hemp, twostriped Leaf chewing is the most common kind of injury produced by grasshoppers. Small plants may be seriously injured by this damage, but well established plants usually will tolerate and outgrow injuries with no ultimate effect on yield. Grasshopper gnawing on stems and petioles cause stems to break, causing more crop injury than does leaf chewing limited to leaves. Damaged areas may break and girdling wounds on stems can cause wilting of areas above the injury site. Late season grasshopper injuries may girdle stems so severely that developing flower buds are killed or their size reduced. 

All grasshoppers associated with hemp have a life cycle that takes one year to complete. Eggs, which are laid in late summer, are the stage that survive winter. Eggs are laid shallowly in soil, in the form of pods, each containing a couple of dozen eggs. This is the life stage that survives between growing seasons and gras/shopper eggs begin to hatch in mid-late spring. In fields that are tilled, most egg pods will be exposed and destroyed; in such settings grasshopper infestations will originate from eggs laid along field edges. Fields that are not tilled, which can occur when plastic mulches are used that remain in place more than a year, have may allow eggs laid in late summer in soil to survive, resulting in grasshoppers being present more extensively throughout a field the following season. The presence of weeds in hemp plantings that support various grasshoppers will also have effects on grasshopper incidence in hemp crops. Some grasshoppers that may occur around a hemp field specialize in certain weedy plants and do not feed on hemp at all. For example, the Russianthistle grasshopper (Aeoloplides turnbulli) is a species that will feed on Russianthistle, kochia, and lambsquarters, avoiding adjacent hemp. A very large grasshopper sometimes found in hemp fields, but does not feed on hemp, is the lined bird grasshopper (Schistocera lineata). 


Southern Corn Rootworm/Spotted Cucumber Beetle


The southern corn rootworm (Diabrotica undecimpunctata), also known as the spotted cucumber beetle, can be found on an extremely wide range of crops, flowers, and weeds. It is most often damaging to melon/squash family plants, but sometimes is a serious pest to ornamental flowers and is regularly present in corn fields. It has been consistently found in hemp fields, particularly in southeastern Colorado. The southern corn rootworm survives between seasons in the adult stage, so they may be seen very early in the season when they emerge from the sheltered areas they use in winter. Flowers and pollen are primarily what they adult insects feed upon and later females begin to lay eggs at the base of larval plants. Various grasses, cucurbits, and legumes are known hosts of the larval stages of this insect, which chew on the roots of these plants. A complete generation can be completed in about two months, and there are likely to be two or more generations per year. The adults are long-lived and can be observed throughout almost the entire growing season. In hemp the adult beetles do a bit of leaf chewing, which produces barely observable, insignificant, leaf injury.


Painted Lady


Peak feeding by the painted lady caterpillars is most common in the early summer. The name “Thistle caterpillar” is sometimes given to this species because during outbreak years these caterpillars may extensively defoliate thistle in the late spring, and then wander in large numbers in search of new host plants which can include common mallow, hollyhock, sunflowers and soybeans. The damage produced by the caterpillar of the painted lady butterfly (Vanessa cardui) is unique and conspicuous, involving the tying of leaves to create a shelter within which they feed. Typically 2-5 leaves may be webbed together and ragged chewing injuries will be evident. The caterpillars within the webbed leaf shelter are notably spiny and early stage larvae are pale brown. Damage to hemp by caterpillars of the painted lady is limited to the foliage, and can be visible due to the leaf tying, but effects on the crop growth and yield are likely to be minimal and insignificant, as the populations of caterpillars rarely reach high numbers due to the presence of abundant natural controls.

As they age,they become variably marked with black and yellow, with a considerable range in the overall coloration. The adult painted lady is a large butterfly marked predominantly with the colors orange and black, with white spots on the tip of the forewing, and dark eyespot markings that occur on both the upper and lower sides of the hind wing. The wing span ranges from 5.0-9.0 cm, with females being somewhat larger than males. 

The painted lady is a highly migratory species that is almost constantly in motion. During the  winter, they vacate most of the US remaining active only in parts of the extreme southwestern states and northwestern Mexico, particularly Baja Mexico. In late spring, they move northward as host plants emerge in spring. The size of these migrations varies tremendously from year to year and is most dependent on the occurrence of spring rains in their overwintering areas. When a favorable precipitation pattern occurs in the southwest, painted lady populations can explode in enormous numbers in the late spring. During these years the painted lady is often the most common butterfly over extensive areas of the western US. In other years with less favorable weather patterns it is much less common. The painted lady butterfly lays its cream colored eggs on leaves, laying a single egg on a leaf. Eggs hatch in 3-5 days the developing larvae construct a loose shelter of silk among the leaves within which they feed and develop. Larval development can be rapid, and is normally completed within two weeks. The full grown larvae then migrate in search of a protected site to pupate. They attach the end of the body with a bit of silk and hang suspended downward before molting to the pupal stage. Initially the pupal stage is in the form of a greenish chrysalis but this changes to a predominantly silver/gray. The adult butterfly emerges in about a week after pupation. Following their annual colonization, there may be several generations produced annually. During late summer painted ladies may be seen in a southerly migration. 


Saltmarsh Caterpillar

The term “woollybear” is given to certain densely haired caterpillars that wander considerably between plants.There are two species of woollybears that may be found on hemp. The saltmarsh caterpillar (Estigmene acrea) and the yellow woollybear (Spilosoma virginica) . The saltmarsh caterpillar occurs throughout much of the United States, except at the highest elevations. Saltmarsh caterpillar are densely hairy. Younger stages tend to be predominantly yellowish, and as they age they darken. However, there is wide variation from orange to nearly black. Indistinct striping may also be present. The adult moths are moderate size with a wing span of 3.5-4.5 cm. The forewings are white with black spotting. Female moths have yellow-orange hindwings and a generally an orange abdomen. Males have white hind wings and an abdomen tipped with white. The saltmarsh caterpillar survives the winter as a full grown larva within a cocoon, hidden amongst leaves and other debris on the soil. Pupation occurs in spring and the adults emerge in late spring. After mating, the female lays a series of bright yellow egg masses on leaves over the course of several weeks. Eggs hatch about 4-5 days after being laid. The caterpillars originally feed as a group, producing skeletonizing injuries to the leaves. As they get older, they individually disperse but continue to feed on leaves for another 3-5 weeks. 

Saltmarsh caterpillars will feed on the leaves of an extremely wide range of broadleaved plants, and on occasion occur in numbers that damage gardens and crops. As they become full-grown, the caterpillars increasingly wander away from their host plant. Ultimately they move to a protected site where they spin a silken cocoon, which is mixed with the hairs of the caterpillar. Within a few days after the cocoon is produced the caterpillar transforms to the pupal stage. Adults,  known as “acrea moths”, emerge from the cocoons in about 2 weeks and produce a second generation in August and early September. Highest numbers of saltmarsh caterpillars will be found in hemp in late summer and early autumn, and late stage caterpillars often are observed wandering on the soil. Damage to hemp by saltmarsh caterpillar is likely to be minimal. Peak feeding occurs late in the season and is limited to foliage. Furthermore the active habits of these insects, moving constantly from plant-to-plant, spreads feeding thinly throughout the crop rather than concentrating it on individual plants. These habits should result in leaf injuries that are insignificant to crop yield.


Yellow Woollybear


The term “woollybear” is given to certain densely haired caterpillars that wander considerably between plants.There are two species of woollybears that may be found on hemp. The yellow woollybear (Spilosoma virginica) and the saltmarsh caterpillar (Estigmene acrea). The yellow woollybear are densely hairy and pale colored - ranging from light brown, to yellow to nearly white. The adult moths are moderate in size with a wing span of 3.8-5.0 cm. The forewings are white with black spotting. Female moths have white wings with a small dark spot in the center. The yellow woollybear survives the winter as a pupa within a cocoon, hidden amongst leaves and other plant debris on the soil surface. Adults emerge over an extended period of time in the spring. After mating, the female lays eggs on leaves of host plants. Eggs are laid in masses of 50 or more and the eggs hatch in about a week. 

Upon the eggs hatching, the young caterpillars originally feed as a group, producing a small patch of skeletonizing injury to leaves. As they get older, the individual caterpillars disperse throughout the crop, feeding on leaves for another 3-4 weeks. Yellow woollybear caterpillars will feed on the leaves of an extremely wide range of broadleaved plants, including many common weeds, and they continuously move through the crop, rarely feeding heavily in a single location. When full grown they move to the soil surface, find a protected site and spin a cocoon within which they transform to the pupal stage. Adults, known as "Virginia tiger moths", emerge in a week or two. Two or three generations will be completed annually, but the generations overlap and caterpillars may be seen from late spring well into autumn. Damage to hemp by yellow woollybear is likely to be minimal. Peak feeding occurs late in the season and is limited to foliage. Furthermore the active habits of these insects, moving constantly from plant-to-plant, spreads feeding thinly throughout the crop rather than concentrating it on individual plants. These habits should result in leaf injuries that are insignificant to crop yield.


Zebra Caterpillar

The zebra caterpillar (Melanchra picta) is a very strikingly colored caterpillar, generally black with white markings and yellow striping. Zebra caterpillar will develop feeding on the foliage of a wide variety of plants including many vegetables, flowers, some field crops, and even a few types of trees. However, it is almost never abundant enough to cause damage to any of these plants as a great many kinds of natural enemies regularly will heavily impact the numbers of zebra caterpillars throughout the growing season. The overwintering stage is a pupa, which occurs in the soil. The adult moths emerge in May/June and females lay eggs in the form of masses, often containing over 100 eggs. Multiple egg masses are normally laid be each moth. Upon hatching, the very young caterpillars feed in a group, chewing the surface of leaves in a way that produces a skeletonizing pattern. As they get older, the caterpillars disperse throughout the plant, chew a bit of foliage, then move to a new area. When full grown, they move to the soil, then create a small chamber in the soil within which they transform to the pupal stage. About a month later, the adult moths emerge, mate and a second generation of eggs and caterpillars are produced on plants. At the end of this generation the mature larvae pupate and remain dormant until the following season. Damage to hemp by the zebra caterpillars is limited to a small amounts of foliage, and can be expected to be minimal and insignificant to the crop yield.


Variegated Cutworm


Variegated cutworm (Peridroma saucia) can be a fairly large caterpillar, generally gray or gray-brown, which is distinguished by the presence of some light spots on the back. It is a type of "climbing cutworm" and a generalist feeder that feeds on the leaves, buds and fruit of a very wide range of plants. Variegated cutworms occur throughout the United States on many crops ranging from mint to apples. It has rarely been significantly damaging to crops. To date the observed presence of variegated cutworm in hemp has been rare. It appears to primarily feed on hemp leaves although this species is known to tunnel into developing flowers and fruit of other crops so it may do some damage to developing hemp buds. 


Yellowstriped Armyworm

Yellowstriped armyworm (Spodoptera ornithogalli) is one of the largest and most brightly marked of the various caterpillars that may be found in hemp. It is a generalist feeder that feeds on the leaves of a very wide range of plants. The presence of yellowstriped armyworms in hemp has only been detected infrequently, and the potential to significantly damage the crop seems minimal.


Tree Crickets

“Regular” crickets will munch on your leaves while “mole crickets” can tunnel under your cannabis plants like moles, and disturb their roots! On rare occasion tree crickets (Oecanthus species) have been found in hemp, and they will chew on the leaves. These are pale green crickets, colored to blend with the vegetation on which they live. Some species will develop on trees and shrubs, but others are more commonly found on lower growing plants, including many flowering plants. Tree crickets lay their eggs inserted into the stems of plants. Eggs are the overwintering stage and they usually hatch in late spring. Immature stages are present in early summer with mature adults present in late summer. The presence of tree crickets in hemp likely result from their movement from flowers, shrubs and other plants around the edge of fields on which they lay their eggs. It is unknown if tree crickets will lay their eggs in hemp; if they do these eggs would be normally killed at harvest.


Slugs / Snails

Slugs and snails usually come out at night, leaving holes in leaves which have scalloped edges from their individual bite marks. They also leave slime trails on leaves and on the ground.

Ants

Ants will eat the stalk of your plants!

Barnacles / Scale Insects

These bugs look like barnacles and stick to the plant on stems and underneath leaves.

Mealybugs

These tiny white bugs look “hairy” and are found crawling on leaves and buds. Mealybugs are common pests of houseplants. They are pink, soft-bodied insects covered with a white, waxy, cottony material. The white “fluff” helps protect them from excessive heat and moisture loss. Unlike their relatives the scales, most species retain their legs throughout their life and can move around. Females are rounded, wingless, and about 1/16″ long.

The citrus mealybug (Planococcus citri) is the most common species found on plant foliage. It feeds on a wide variety of plants, and especially likes soft-stemmed and succulent plants such as coleus, fuchsia, croton, jade, poinsettia and cactus. It also shows up consistently on rosemary, citrus, and bird of paradise. Other mealybug species such as longtailed mealybug (P. longispinus) or cactus mealybug (Hypogeococcus festerianus) occasionally occur on specific host plants. These species remove plants sap from aboveground plant parts, especially stem tips, leaf junctures and new growth.

Their feeding weakens and stunts plants, and causes foliar yellowing, defoliation, wilting and general plant decline. In some cases, plants can be killed. Citrus mealybugs inject a toxin while feeding that causes plant malformation. Mealybugs also excrete honeydew, which allows for the growth of sooty mold. Some mealybugs are root-feeders. The ground mealybug (Rhizoecus falcifer) is the most common soil mealybug, occurring on the roots of many house plants, especially African violets. Feeding on the root hairs results in yellowed leaves, wilting, stunting and bloom reduction. A few mealybug species will move to roots when growing conditions are less favorable, but return to stems and leaves when plants are actively growing. Female citrus mealybugs lay up to 600 small (1/100 inch or 0.3 mm long), yellow eggs within a protective mass of white, cottony threads. The longtailed mealybug does not lay eggs but produces live young, similar to aphids. After depositing the egg mass or live young over a period of 5–10 days, the female mealybug dies. The immatures search for feeding sites on which to settle. Male nymphs settle and spin an elongated, white waxy cocoon. Females have three instars and are mobile throughout their lives.

The best method for detecting infestations of mealybugs on leaves and stems is visual inspection – just looking at the plants. Both the insects themselves and the eggs in their masses of waxy threads may look like white cotton on the plant. On some plants mealybugs concentrate on the growing tips, and on other plants they are more dispersed. The longtailed mealybug frequently conceals itself in leaf whorls.

Underground infestations are more difficult to detect. Yellowed or wilting foliage may indicate the presence of mealybugs on the roots. Small white cottony masses around the drainage holes of pots also indicate the presence of mealybugs but in many cases infestations can be confirmed only by removing the root-ball from the pot to observe mealybugs on the roots.Mealybugs are difficult to get rid of because immatures typically wedge themselves in stem crotches, leaf folds, or other tight locations where washing or pesticides cannot reach them. The best way to control mealybugs on houseplants is to prevent them from being established in the first place. Carefully inspect all new houseplants before introducing them to your home, and keep them separate from other plants for a week or so if possible. Mealybugs can easily crawl from one plant to another, especially when leaves or branches overlap, so one contaminated plant could spread mealybugs to all your houseplants. Check under leaves, in new leaf folds, and around the growing tips for signs of infestation. Mealybugs like lush foliage, so avoid over-fertilizing with excess nitrogen.

Whiteflies/ White fly

Whiteflies look like tiny white moths and hang out under your cannabis leaves.


  Insects/Mites that Suck Fluids from Leaves  

Cannabis Aphid

Aphids live under leaves & have different forms depending on their stage of life. Cannabis aphids, Green peach aphids (Myzus persicae), cotton/melon aphids (Aphis gossypii), and bean aphids (Aphis fabae) are among the aphids that have been reported as feeding on hemp. Cannabis aphids are fairly typical of most other aphids, which can become mature adults within a couple of weeks or so after birth. (Development is always strongly related to temperature.) Adult females may give birth to perhaps 1-5 young per day for their remaining life, a 3-4 week maximum. These are a light colored species early in the season (cream colored to pale yellow). Late in the season, shortened day length triggers changes in their coloring, and the colors will range from light green/pale pink/light brown predominate. The ultimate adult form is normally wingless, but some are winged and winged stages may be particularly common to see in the late summer. Some dark spotting occurs on winged forms. Wingless forms lack this patterning, but may have pale striping running along the top of the body. Cannabis aphids normally reproduces asexually - only females are present and they hatch their eggs internally giving live birth to genetically identical daughter aphids. Mating occurs once a year, and then the female will lay eggs on leaves, flowers and stems. This is the only time of the year externally laid eggs are present. The egg is used for the surviving stage of the aphids. Eggs of cannabis aphids are laid in late September on the leaves around the buds. These eggs can remain dormant throughout the winter and hatch in the spring the following year. If there are live plants/volunteers present in the field during egg hatching, then the aphids may colonize these plants. Eggs of most aphids produced in this manner require a chill period in order to hatch.  The hatching is then triggered by increasing day length. If there is a live hemp plant growing near the hatching eggs, the aphids may be able to make it onto this host plant and begin the first generation.  If fields are rotated and tilled, this can eliminate eggs from hatching. The survival of cannabis aphids more often occurs indoors, maintained through winter on live plants and moving outdoors on infested transplants. There are numerous natural enemies of cannabis aphids that are normally present in outdoor hemp fields (e.g., lady beetles, flower flies, green lacewings, parasitoid wasps) and these can effectively curb outbreaks. Where natural enemies are present, aphid survival will average a much shorter period.  In indoor planting the natural enemies are normally not present, unless introduced.

Cannabis aphids (Phorodon cannabis) are found on the leaves and stems of Cannabis. Cannabis aphids feed on the fluids of the plant phloem, which it extracts through its "piercing-sucking" mouthparts. Very little injury occurs to cells from this feeding, so there are no symptoms on the leaves, such as white flecking or surface scarring, which is produced by spider mites or thrips. Damage is caused by the loss of plant fluids. When high numbers of aphids are present and sustained this can cause reductions in plant vigor that can result in slowed growth, wilting, and leaf yellowing.Very high populations of cannabis aphids have been observed in outdoor crops during late August and early September.  As cannabis aphids feed, they also continuously excrete a sticky fluid, known as honeydew. This is produced in the form of tiny droplets which drop onto leaf surfaces below where it can be noticed as small shiny spots. This excreted honeydew can be an excellent diagnostic sign for detecting cannabis aphid infestations. As cannabis aphids grow they must periodically shed their external "skin" (exoskeleton) and as they produce a new and larger exoskeleton for the next, larger life stage. These "cast skins" will collect around colonies of aphids and often drop onto leaves below an aphid colony. Along with honeydew, the cast skins can be an excellent diagnostic sign for detecting cannabis aphid infestations. 


Rice Root Aphid

Rice root aphid (Rhopalosiphum rufiabdominalis) is a dark olive-green insect with a generally round body form. Wingless stages develop on the roots and they survive on plants grown both in soil and in hydroponic culture. Winged stages periodically emerge from the soil to fly to new plants, which are most often observed when they have been trapped by the hairs on the upper surfaces of leaves. Rice root aphids have so far only been found associated with indoor Cannabis production. However, rice root aphids are well-known as an aphid that can be found year-round outdoors in much of North America. This aphid has a wide host range, but is most often associated with the roots of various grasses, including wheat and barley. Infestation of Cannabis plants can occur if plants are taken outdoors and exposed to colonizing by winged forms of the aphids.. Year-round reproduction can occur within indoor hemp growing facilities. Reproduction by rice root aphids is entirely asexual; no males are produced and females give live birth to genetically identical daughter aphids. They develop rapidly and will mature in about 9-10 days. The adults can live for about a month during which time they can produce several new daughters each day. At an optimal temperature, rice root aphid populations can double every 1.6 days.


Leaf-hoppers

These bugs come in almost every color known to man so sometimes it can be tough to tell what they are just from looking. However, they all make clusters of spots on your leaves where they’ve sucked out all of the sap, so if you see spots like this you know you’ve got leafhoppersLeafhoppers are small insects (1/8-1/6 inch) that have an elongate body. The adults, which are winged, readily jump and fly from plants when disturbed. Immature stages (nymphs) are wingless but can actively crawl on plants. The adults of at least six species of leaf-hoppers have been collected in sweep net samples associated with hemp. Most regularly found is Ceratagallia uhleri, which is one of the few leafhoppers found on hemp that can also reproduce on the plant. No visible plant injury has ever been observed by this leafhopper. Another leafhopper, a small light green species tentatively identified in the genus Empoasca, also reproduces on hemp. Sampling of hemp has resulted in recovery of only adult stages of most of these. Most leafhoppers observed on hemp leaves appear to develop on other off-field plants. They may feed briefly on the plants, or may not feed at all on hemp. Leafhoppers feed on leaves and stems with piercing sucking mouthparts that extract a bit of fluid from the plant. Most feed on fluids moving through the phloem of plants, resulting in insignificant effects on plant growth and no visible symptoms. A few leafhoppers, notably an Empoasca species extract fluids from cells of the mesophyll, producing a small, light flecking injury (stippling) at the feeding site. Leafhoppers found on hemp do not produce feeding injuries capable of causing any significant damage to the hemp. This situation is different in the eastern United States where the potato leafhopper (Empoasca fabae) is present.


Curly top Beet Leaf-hopper

Beet leafhoppers are fairly similar in the size and the general coloration of some of the many other leafhoppers found in hemp. This makes it difficult to identify them. Adults are pale green/light yellow with some blotches, and an elongated slightly wedge-shaped body that is about 1/8-1/6 inch in length. Adults are the only stage that would be found on hemp, because this insect does not reproduce on the crop. During the winter, this insect is able to survive on various kinds of weedy plants that continue to grow through winter, particularly the mustard-family. The abundance of winter host plants in the southern breeding areas could be an important factor in the number of beet leafhoppers that appear in the spring. Many of the beet leafhoppers carry with them the beet curly top virus they acquired when earlier feeding on beet curly top infected plants. Beet leafhoppers survive through the winter where winter annual mustards, such as flixweed and pepperweed, are present and in good condition to support the insects. This would happen most often when winters were mild and moisture was good. Severe, dry winters would reduce the potential of beet leafhoppers to overwinter within the state. During late spring and summer beet leafhoppers can be found on a great many plants but will reproduce on only some of these. Russian thistle is the best known weed host for summer breeding by the beet leafhoppers and where but there are likely many others. Kochia is the plant on which beet leafhoppers are most easily found. Regular surveys of kochia patches should allow one to detect when migrations have moved into the region and are the best plant to survey to get a sense on the relative size of beet leafhoppers populations from season to season. In hemp, adult beet leafhoppers will only be present and these likely will spend little time in the crop, feeding some but then moving to more favored food plants. The detection of beet leafhopper is best done by sampling plants with a sweep net. 

The Beet Leafhopper is one species of leafhopper, which can produce serious damage.The damage produced by the beet leafhopper is due to its ability to transmit (vector) a virus to the hemp, known as the beet curly top virus. This disease produced in hemp can cause a wide range of growth disorders and can seriously damage the plants. This disease produced a very damaging outbreak during 2019 in parts of western Colorado. Beet curly top is a notoriously difficult disease to manage on any crop. Because of the mobility of beet leafhoppers and the rapid speed (a couple of hours) which the virus is transmitted, insecticides are ineffective. Reflective surface mulches, which deter beet leafhoppers and other insects (e.g., aphids) from landing on the plants, may have some value in reducing beet curly top virus spread in hemp.

The Beet Curly Top Virus has been observed to produce an extreme wide range of symptoms in hemp. During the early stages of infection, leaf symptoms may be quite mild, producing only a slight yellowing, mostly at the base of a leaf. In more severe cases whole plants will become pale yellow, often with some slight upward leaf curling, and the plant will become generally stunted. Other hemp plants may show strong twisting of the new growth, which may remain green or turn yellow. Some stunting will also occur. Hemp infected with beet curly top virus also has shown some very strange symptoms that appear to be unique to the crop. In some cases, plants that show strong leaf curling appear to be able to later outgrow most of these symptoms. Another peculiarity often observed is that plants may be “bisymptomatic” where some of the same plant shows symptoms and other parts do not. This most commonly occurs when the original stem develops leaf twisting and becomes stunted. Side branches developing off of the main stem are then stimulated to grow and these often appear normal. Interestingly, in these plants, beet curly top virus is detectable in both the original main shoot and the side branches that do not show symptoms.The reason for this wide range in symptoms that can appear is unclear but may involve such things as genetic differences in a plants response to the virus or differences in the strains of the virus. There are several strains of beet curly top virus, but the Beet curly top virus has only one insect (vector) capable of allowing the virus to be transmitted to plants, and this is the beet leafhoppers. All infections of hemp occur when a beet leafhopper that is carrying the beet curly top virus (after previously feeding on a BCTV-infected plant of some kind) feeds on a hemp plant. 

Potato Leaf-hopper

The Potato leafhoppers (Emposaca fabae) occur mostly in the eastern half of North America.The Potato leafhoppers may have more potential to cause significant yield loss to hemp than any other leafhopper associated with the crop.  This is because the Potato leafhoppers produce hopperburn symptoms on many kinds of plants and can cause serious yield loss to many crops such as alfalfa, beans, hops and potatoes. 

Hopperburn is produced by a plants reaction to the unique way that potato leafhoppers feed. They have piercing-sucking mouth parts (that are typical of other leafhoppers) that they use to rupture the cells, and then feed on the cells fluids that are released. Then the saliva that is introduced as it feeds has toxic effects that further damage the cells. By disrupting these tissues, the movement of the nutrients is disrupted and the sugars accumulate in the leaves. This is the plants response to the feeding injuries, which will produce the condition known as hopperburn. Hopperburn symptoms on plants typically show a yellowing at the tip of the leaves. These symptoms may progress to include the entire leaf and is often followed by areas of leaf death. Leaf curling may also occur. Sharp reductions in photosynthesis and stunting are other symptoms that have been observed on some plants. Differences in response to injury may be expected to vary among hemp cultivars, as it does with other crops. 

False Chinch Bug

False chinch bugs (Nysius species) are one of the most commonly encountered plant feeding insects. They can be found on a wide variety of plants, but mustard family plants are particularly favored. Flixweed and other winter annual mustards (such as winter canola) are critical to their survival between growing seasons but other plants, such as kochia and pigweeds, can be important hosts in the summer. False chinch bugs will be found in hemp throughout the growing season. Occurrence of noticeably large numbers early in the season will likely only occur if large areas of winter annual mustards in the near vicinity are cut or rapidly dry down, forcing migration of the insects. False chinch bugs will also migrate into hemp when it flowers in the late summer, as alternate weed hosts dry out and become less available. False chinch bugs are highly migratory; their appearance in hemp can be sudden - and their disappearance may be similarly sudden. False chinch bugs feed by sucking fluids from leaves of plants in a manner similar to Lygus bugs (“lacerate and flush”). However, their ability to cause injury to leaves, buds and seeds appears to be far less than what is produced by Lygus bugs. It can be expected that measurable damage to hemp foliage by false chinch bugs would only occur when extremely high populations occur on plants for a period of many days-weeks and even in those cases usually only a couple of leaves will show visible wilting or dieback symptoms. The damage that false chinch bugs may produce to hemp has very little potential to cause effects on yield.Numbers of the wingless nymphs can be extraordinarily high in some situations, and often cause alarm when observed, but have never been observed to cause any visible injury to hemp crops.


Lygus Bugs

Lygus bugs are very commonly found in crops, gardens and natural areas throughout the state. The most common species found in hemp is the pale legume bug (Lygus elisus). Two other species found in most any crop grown are the western plant bug (Lygus hesperus) and the tarnished plant bug (Lygus lineolaris). There are hundreds of plant species on which Lygus bugs will develop. Legumes (e.g., alfalfa, peas, vetch) and mustards (e.g., flixweed, canola) are perhaps the most important plant families that support Lygus bugs, but they are also associated with a great many other kinds of herbaceous broadleaved plants. Migrations into hemp may accelerate as nearby sources of these these plants mature and dry down or are cut/harvested. Lygus bugs feed by sucking fluids from plants. During the course of this feeding they will destroy cells at the feeding site, a kind of injury (“lacerate and flush”) that is much more destructive than what occurs from feeding by other sucking insects such as aphids and leafhoppers that feed by tapping into the fluids of the phloem. Furthermore, feeding is concentrated on younger tissues, such as emerging leaves, flowers, and developing seeds. Effects from Lygus bug feeding include distortion of new growth, flower abortion, and deformities of seeds. Damage to hemp by Lygus bugs is likely to be minimal, although they have effected many kinds of crops where seed production is important, as they can reduce seed production and quality. This may be a potential issue in hemp being grown as and oilseed crop.


Red-shouldered Stink Bug

The red-shouldered stink bug (Thyanta custator) is one of the larger and more conspicuous insects that one might see on hemp plants, with almost ½-inch in length with a broad body form. Most often they are pale green, although some having more brownish coloration. A faint red band often is present across the body in the area behind the head. Red-shouldered stink bug feeds on many kinds of plants and can be common in wheat, beans and alfalfa. They feed with piercing-sucking mouthparts on the young leaves, flowers and developing seeds but appear to cause little overall injury to the plant. The injuries this insect are reported to cause involve the plants seed production. Migrations of adult insects into hemp may occur in midsummer as small grains and weedy hosts mature. The red-shouldered stink bugs will most always be noticed around buds and developing seeds. Damage to hemp by red-shouldered stink bugs is likely to be minimal and limited to injury and potential abortion of some seeds. Eggs and nymphs have been found in hemp, suggesting that it may successfully reproduce on the crop, but populations are low and occur late in the season. 


Conchuela and Say’s Stink Bug

Both the conchuela (Chlorochroa ligata) and Say's stink bug (C. sayi) can be found in a great many crops and common weeds. Both are moderately large (length 13-19mm). Say's stink bug is consistently green, but the conchuela can be highly variable in color, ranging from dark brown, to reddish brown to green. A single light spot is present at the tip of the triangular plate (scutellum) on the back of the conchuela; Say's stink bug also has three light spots on the front of this triangular plate. Winter of both species is spent as an adult, hidden under plant debris and other protective cover, and they emerge in spring to feed on plants. Legumes are particularly favored by the conchuela with alfalfa being an important early season host in many areas. Say's stink bug tends to feed more often on grasses, with winter wheat an important early season host. Egg laying by the conchuela may begin in mid May and continues through midsummer. Eggs are laid in masses, each averaging about 30 eggs. Eggs hatch in one to two weeks and the newly emerged nymphs will typically remain clustered about the eggs for a few days, before dispersing. Flowers and developing seeds are favored feeding areas, but they will also feed on leaves. Feeding occurs with piercing-sucking mouthparts that extract plant fluids. Some localized injury occurs at feeding sites, which may appear as a small discolored area, and developing seeds may be deformed or abort. It takes about between 35-60 days after egg hatch for the developing nymphs to reach the adult stage. The adult insects continue to feed until early fall, then move to sheltered sites to survive winter. Adults of the conchuela sometimes show aggregation behaviors and may appear clustered on plants or, sometimes, on the sides of buildings. Life history is generally similar with Say's stink bug except it may produce two or more generations per season; the conchuela only produces a single generation. Damage to hemp by these stink bugs is likely to be minimal, largely limited to injury and potential abortion of some seeds. They are unlikely to ever become very abundant in fields and can be expected to be concentrated along field edges.


Thrips

Thrips leave irregular bronze or silver marks that may look like “dried spit” or tiny snail trails. Their young look like fat, tiny worms. At least two species of thrips are regularly associated with outdoor-grown hemp, onion thrips (Thrips tabaci) and western flower thrips (Frankliniella occidentalis). Both are very small insects with an elongated body, typically about 1.2-1.5mm (about 1/15-inch) in length. Thrips feed by piercing surface cells of leaves and sucking out the cell contents. This results in a small light area, known as a stippling injury, at the feeding site. This injury is somewhat similar to that produced by the two-spotted spider mite. Under normal field conditions such injuries are widely dispersed through the plant and attract very little, if any, attention. When thrips populations are sustained at high levels cumulative injuries can cause extensive leaf scarring. Also, thrips that feed on expanding immature leaves may cause some leaf distortion. Such numbers are unlikely to occur in outdoor crops, where natural controls of thrips are robust. On indoor crops noticeable leaf injury is more likely to be observed.  Onion thrips and western flower thrips are well known pest of many indoor/greenhouse crops grown. Both have a very wide host range of plants on which they can develop. Of the two species, western flower thrips is more commonly associated with flowers, but may also develop on the leaves of plants such as winter wheat and legumes such as alfalfa and beans. The western flower thrips will also feed on the pollen. Onion thrips develop on leaves of many common weeds and vegetable crops. 

Developmental Stages: Thrips eggs are inserted into plant tissues. The egg will normally hatch within a couple of days after being laid and the stage that follows (Instar I) is tiny and wingless. It feeds on the leaves and within a few days will molt to a larger second stage (Instar II) that feeds more extensively on the plant. After this stage is completed it molts again, but to a nonfeeding form (Instar III) that may occur in soil or in leaf axils. Another molt occurs (Instar IV) with the thrips in the same site, that also is non-feeding stage, which further transitions its development. After the next molt, a winged adult form emerges to repeat the cycle. The time required to complete a single life cycle of both onion thrips and western flower thrips is dependent on temperature. Under normal temperatures during a growing season thrips can complete a generation in about 2-3 weeks. Multiple generations are produced annually, and outdoors thrips can continue to survive and develop (at a slowed rate) on available living plants that are present through the cold months (e.g., winter annual mustards, certain hardy perennials). On outdoor-grown crops thrips are subject to many natural controls, including predators such as minute pirate bugs. On confined indoor crops thrips may develop in higher populations, and the damage they do can cause extensive leaf scarring. 


Twospotted Spider Mite

Spider mites are often caught from another grow room, and their bites leave small white speckles all over your leaves. They’re so small they can be hard to see, though the best place to look is underneath the leaves. You may see webbing if there’s enough of them living on the plant. The two-spotted spider mite (Tetranychus urticae) is one of the most damaging spider mite species. In outdoor grown crops it can be injurious to an extremely wide range of plants, ranging from corn to pears. In yards/gardens it may be present on plants such as eggplant, beans, raspberries, roses, marigolds, and several deciduous shrubs. It is very common on indoor-grown plants and is almost always the species damaging houseplants, certain indoor-grown vegetables (e.g., cucumbers, tomatoes), and herbs. It is also a potentially serious pest of indoor grown Cannabis. The two-spotted spider mites are probably the largest arthropod pest to worry about on indoor grown hemp, largely due to the absence of the more important natural controls in these conditions. On outdoor-grown hemp, where natural controls are normally present (e.g., adverse weather events, predators), the two-spotted spider mite are likely to rarely, if ever, cause insignificant injury to the crop.

The adult two-spotted spider mite is quite small, about 0.4 mm (ca. 1/20-inch), and is usually straw color to green. There is a pair of large darker spots on the side of the body. Both males and females are produced, with adult males being somewhat smaller than females. Females lay eggs on the surface of plants, usually on the underside of leaves, and the eggs are quite large in relation to the size of the mother. Eggs, and the shells of eggs that remain after hatching, can be very useful indicators for detecting the presence of spider mites. Within a day or two after being laid, a minute six-legged stage (larva) emerges from the egg and begins to feed. It subsequently sheds its exoskeleton (molts) to a slightly larger 8-legged stage. Two molts follow and the adult form is produced which soon mates and begins to produce eggs. Under optimum conditions of high temperature and low humidity the entire life cycle is completed in just over a week. A life cycle of 12-15 days is more likely to occur under the conditions of indoor-grown hemp. Regardless, the life cycle is short and numerous generations will be produced in a 2-3 month period, potentially resulting in many thousands of spider mites during the course of a crop cycle. Reproduction also may accelerate after flowering begins due to changes in the nutritional quality of plants that are favorable to spider mites. Outdoors, two-spotted spider mites can survive the winter under leaf litter and other protective cover. Prior to overwintering they become semi-dormant and slow their metabolism, going into a condition known as diapause. The spider mites in diapause usually are oranger, rather than the yellow-green during their active feeding periods. Changes in day length (short days) and cooler temperatures are most important in causing spider mites to go into diapause. Under continuous conditions of warm temperatures and suitable light/dark periods (greater than 10 hours of light), such as occur with indoor production, the two-spotted spider mite will not undergo a dormant period. 

Hemp Russet Mites

These mites are so small you will likely never see them even under a magnifier. However, you can tell your plant has been infected because your new leaves will be blistered, twisted and glossy. The overall plant will also be growing poorly and if it’s flowering the buds may turn brown. Broad mites and russet mites are often mistaken for other problems like nutrient deficiencies or  heat stressor pH problems. Hemp russet mites (Aculops cannibicola) feed on the surface layer of plant cells by piercing them with their minute mouthparts and then feeding on the cell fluids. No visible symptoms are produced when the russet mites are in low populations, but a range of subtle symptoms develop during outbreaks. In heavy infestations, plants leaves are often duller in color, appearing slightly grayish or bronze (russeting). Leaf size may be reduced and foliage becomes more brittle. In some cultivars a slight upward rolling of the leaf edge is produced, but this symptom is not consistently produced by hemp russet mite and also can be produced by other causes. Hemp Russet mites also develop on stems, which may cause stems to have a slight bronze/golden color. Most damage occurs to developing buds. Heavy infestations can seriously suppress bud growth and size. The most serious damage reported to hemp in Colorado involves the maturing buds/flowers of all-female clones grown for CBD production. Extremely high populations of mites may build in the late summer, which damages these tissues and reduces the final yield and quality of the crop. During heavy infestations flowering structures may take on a beige appearance, the combined result of leaf injuries and the color of the mites that are observed. Cannabis is the only reported host for hemp russet mite.  The attempts to establish it on related plants in the Cannabaceae family (hops, hackberry) have so far been unsuccessful. 

The biology of the hemp russet mite is very little studied but is likely similar in general outline the related species of eriophyid mites (e.g., tomato russet mite Aculops lycopersici) that feed on the surface of herbaceous plants. Eggs are produced that hatch within two days. A minute immature stage (larva) emerges from the egg, and a couple of days later it will molt to the larger second stage (nymph). A few days later there is a final molt, producing the adults. Both males and females are produced. The entire life cycle (initially laid egg through first egg laying by the adult) is reportedly completed within about two weeks at temperatures of 77F. Egg production by tomato russet mite is reported to typically average between 1-2 dozen per female. Adults of tomato russet mite will normally live about 3 weeks. No special stages are produced that would allow extended survival, such as an egg that can remain dormant for an extended period. However, tomato russet mites are capable of surviving for an extended time between growing seasons on various nightshade plants and on bindweed. During winter, reproduction ceases, and they are semi-dormant. Hemp russet mites appear capable of surviving and reproducing year round on Cannabis crops grown indoors in continuous culture. However, significant questions remain about how hemp russet mites may survive outdoors between seasons. In June 2018 hemp russet mites were found on leaves of volunteer hemp growing adjacent to a shed used to dry the crop of the previous season. This suggests that some hemp russet mites may survive outdoors in Colorado under certain conditions, although it is not clear on what kinds of plants they would be sustained in the absence of live hemp. On their own, hemp russet mites can crawl only very short distances and immature stages are particularly immobile. However, adults are capable of some crawling and may move to the edge of leaves where they can then be picked up and carried on air currents; in enclosed areas, fans can quickly spread mites. Outdoors small breezes can distribute mites through fields.


Stilt Bug

Stilt bugs (Jalysus spp.) can be found visiting many crops and have been observed in hemp. Their unusual appearance, a very thin body combined with extremely thin and long legs, make them a curiosity. Stilt bugs develop primarily by feeding on small insects and insect eggs, and they are a minor component of the natural enemy complex within hemp. They may also occasionally drink fluids from plant with their piercing-sucking mouthparts, but such feeding would not produce any effects on hemp plants.


  Insects that Tunnel into Stems/Branches  

Leaf Miners

Leaf miners are larva that actually live inside your leaves and tunnel through them to eat! Are your Cannabis leaves suddenly looking like the snaky maze aftermath of a Light Cycle tournament from Tron? Chances are pretty good that you’ve got hungry little Leaf Miner maggots tunneling through the juicy interiors to feed on plant cells like Ms. Pac Man chomping on a power pellet. Once sated, after a week or two of tunneling, the maggots will emerge from the leaf, drop to the ground and pupate, quickly metamorphosing into a small adult fly. The mated females will soon inject their eggs below the surface of a healthy mature leaf to start the cycle anew.

Every leaf is a food factory powered by the sun, manufacturing all a plant needs to grow utilizing raw materials gathered from the air and soil. When Leaf Miners are eating up that cellular factory material, your crop yield is going to suffer somewhat, but thanks to natural predators like parasitic wasps (so long as you don’t kill your beneficials with broad spectrum insecticides) it is unlikely that Leaf miners will do major damage. A worrisome secondary effect of Leaf Miners is that the egg insertion and pupa exit wounds at the two ends of the tunnels can serve as entryways to various pathogens, further weakening the plant. The egg end of the tunnel is understandably tiny, the path of destruction gets wider as the maggot grows, you can see clearly how quickly things progress. If upon inspection you find a leaf with just one or two short squiggly tracks, use your hand lens to identify the maggot at the wide end of the tunnel and simply squish it in place, allowing the healthy remainder of the leaf to continue its good work. Leaves laced with multiple serpentine tracks should be removed, quarantined and destroyed.

Leaf Miner maggots are very difficult to kill since they are shielded from soap sprays and suffocating oils by living underneath the leaf epidermis. Additionally, Leaf Miners have developed some resistance to some of the harsher insecticides which you shouldn’t be using anyway in this new age of residue testing. If allowed in your locale, Spinosad is very effective against the feeding maggots; they eat it, stop feeding and die. Spinosad is generally accepted as a safe organic, but please do take care to not use it around honeybees. Companion plantings of lambsquarter, columbine, and velvetleaf may reduce the amount of infestation on your Cannabis as the adult flies choose a more perfect host for their next generation of maggots to feed within.


Eurasian Hemp Borer

The Eurasian hemp borer (Grapholita delineana) is the caterpillar (larval) stage of a small moth that tunnels into the stems and buds of Cannabis. It is also known as the Eurasian hemp moth and hemp borer. Most of the observed damage by this insect occurs when the caterpillars (larvae) tunnels into the base of developing buds, girdling the stem at the base of the bud, which then wilts and dies. Leaf wilting and die back of terminal growth can occur from stem tunneling, and may also cause some stunting and distortion of the stems and stalks, perhaps with some effect on the final yield. Damage to the developing seeds have also been reported. The Eurasian hemp borer has potential to be a significant pest of hemp crops grown for pharmaceutical purposes (e.g., CBD) and seed. It will also likely become more commonly encountered in the crop as hemp cultivation continues and expands. 

These caterpillars are quite small, reaching a maximum size of about 6-8 mm. The early stage of these caterpillars are cream colored with a dark head. The last stage of these caterpillars have a reddish-orange coloration. The last stage larvae are much more commonly noticed than younger larvae that blend in with the plant. Often they are noticed during harvest or when they get dislodged from plants during drying. The full grown caterpillar often survives the winter in small stems near the top of the plant, or within folds of the leaves around the seed heads. The caterpillar remains dormant through the winter, transforming to the transition pupal form in the spring. Pupation usually occurs within the plant. T Eurasian hemp borer larva in stem at the base of a bud. Adults later emerge in mid spring and begin the first of two, probably three, generations that are completed during the course of the growing season. After mating, the female moths can lay a few hundred eggs over the course of a couple weeks. Instantly when the eggs hatch, the first stage caterpillars feed for a few days on the leaf surface. As the caterpillars get a bit older and larger, they then bore into the stems of the plant. From that point the remainder of their life will occur within the plant, as a stem/stalk borer, until they reach the adult form that begins a new generation. Adults that develop from the eggs laid during spring produce a second generation that results in caterpillars (larvae) present in plants during midsummer. It is likely that a third generation occurs, with adults present through late summer. These late season moths lay eggs that result in the caterpillars that do the most injury to plants. These last generation caterpillars then go dormant, resuming development the following spring. In addition to Cannabis, Eurasian hemp borer is also reported to develop in hops and knotweed (Polygonum). Wild host plants appear to be important in sustaining populations that later infest hemp. These alternate wild plant hosts used by Eurasian hemp borer presently are unknown but perhaps include various weeds in the family Polygonaceae (smartweeds, knotweeds) with stems large enough to support this insect. 

Since Eurasian hemp borer survives the winter as a larva within stems, removal of all crop debris (stems, stalks) should largely eliminate overwintering populations. This normally occurs when plants are cut at the base and removed from the fields for processing. Mechanical harvesting that leaves some residue may allow some survival, although stem crushing during harvest would likely kill most larvae. If any are found hosting this insect, these weeds should be destroyed in a way to kill the insect in the stem, before adult moths emerge in spring. Since some larvae may become dislodged and survive in drying shed, crops should not be located near (within a 1/2 mile) of these buildings. The use of insecticides is problematic for this situation for at least two reasons. One is that the larvae are present for only a brief period on the outside of the plant where they would be exposed (this occurs during the first few days after the eggs hatch when the very young caterpillars feed on the leaves). After this point they tunnel into the plant and are inaccessible to treatment. Insecticide options are very limited for hemp and only consist of insecticides that are considered to be allowable by the state Department of Agriculture. 

In Colorado, the list of allowable pesticides includes several formulations of Bacillus thuringiensis var. kurstaki (Deliver, Dipel, Javelin, Thuricide, etc.) that could kill young larvae feeding on the exterior of the plant. The Eurasian hemp borer is a weak flier and initially infests field edges so these areas should be targeted. Presently the best way to tell when adults are present and laying eggs is to observe the presence of the moths, either visually while walking the field or in a sweep net. At this time, there are no pheromone traps that will capture this insect.

European Corn Borer

The European corn borer (Ostrinia nubilalis) is another stalk boring caterpillar. These caterpillars are light brown or cream colored, never reddish-orange. They also get much larger than the Eurasian hemp borer (ca. 20 mm). The European corn borer develops in the stalk and larger diameter stems and would rarely be associated with the area around the developing buds and seeds. 

The developing stages (larvae/caterpillars) of the European corn borer develop as a stem/stalk borer. In addition to corn, many plants hosts this insect including peppers, snap beans, chrysanthemum, dahlia, and several other ornamentals. Stems of seedling trees are also sometimes damaged by larvae. During the peak period of US hemp production, within the Midwestern states in the 1940s, the European corn borer were the insect mentioned as being most often observed to damage the crop. The stage of the European corn borer that occurs within plant stems is a creamy to grayish larva, with some indistinct rows of small, round, brown spots running the length of its body. A full-grown larva is about one inch long. The European corn borer spends the winter in the stage of a full-grown larva within plant debris it fed upon during the late summer/early fall. Pupation occurs in the spring, and the adults emerge in the late spring. Adults typically aggregate and mate in dense grassy “action sites”, then females lay eggs in the form of masses on the foliage. Early-stage larvae often tunnel into leaf veins, later moving into stalks or fruit as they get older. Pupation occurs in the plant, and there is usually a second generation in August. Based on historical accounts, the European corn borer has potential to be a significant insect pest of hemp. Stem and stalk tunneling may reduce yield and can also cause structural weakening that can cause stem/stalk breakage.


  Insects/Mites associated with Buds/Flowers/Seeds  

Lygus Bugs


This information is listed above.


Hyaline Grass Bug

The Hyaline grass bug (Liorhyssus hyalinus) can be a common insect in flowering hemp with developing seeds. The adults move into hemp from various weed hosts on which they develop on early in the season. Adults then begin to lay masses of reddish eggs, usually on small leaves or among flowers and developing seeds. The newly emerged nymphs that hatch from these eggs are initially reddish but become more straw colored or mottled as they get older. Almost all of these insects in hemp are present in the vicinity of the seed head where it is thought that they feed on flowers, developing seeds, and foliage, sucking fluids with piercing/sucking mouthparts. Sometimes a collection of rusty colored fluid excreted by the insects may be visible on the leaves in the seed head. Hemp appears to be a favored crop and egg laying has been observed to occur continuously into October, when plants are harvested. Some further development also has been noted in harvested seed heads as they dry. Overwintering stages of hyaline grass bug in Colorado may be a mixture of both adults and nymphs, as occurs with false chinch bug. In spring various winter annual or perennial weedy hosts support this insect, including prickly sowthistle, red-stem filaree, and cheeseweed. (Despite its common name, this insect does not breed on grasses.) No obvious damage to hemp by hyaline grass bug has been observed. Feeding on developing seeds may have some effects on seed viability and this needs further study.


Red-shouldered Stink Bug


This information is listed above.


Conchuela and Say’s Stink Bug


This information is listed above.


Corn Earworm


The Corn earworm (Helicoverpa zea) is an insect found throughout North America and is a serious pest of many crops, including corn, tomatoes, peppers, and cotton. It is an insect that will tunnel into the buds and developing seeds of hemp. This insect has shown the most potential to damage hemp, and during outbreaks this insect has caused serious damage to CBD cultivars of hemp grown in eastern Colorado.Potential damage to fiber or seed producing cultivars is likely to be minimal.  Corn earworms do not develop within the stems,  and they feed at the base of the developing buds, gouging the base of the bud which then dies. An individual caterpillar may move through a plant and damage several buds during the last week of its life when it nears full-growth and causes most injury.  This is one of the most widespread and commonly damaging insects in much of the United States, affecting both field crops and vegetable crops. 

Evidence of its importance is indicated by it having three accepted common names: corn earworm (when in corn), tomato fruitworm (when feeding on fruits of peppers, tomatoes, etc.), and bollworm (when feeding on cotton bolls). It can be a fairly large caterpillar, reaching about an inch (25 mm) when full grown, and is highly variable in color with green and mottled black forms usually predominating. Populations of this insect vary greatly from season to season. This insect will usually move into hemp in late summer with peak injury occurring after plants begin to flower during late August and September.  Corn earworms have historically been able to survive through winter, as a pupa in the soil. Adults of the corn earworm are strong flying moths and disperse long distances. Many of the corn earworms that occur in fields may have migrated many hundreds of miles. The adult moths fly at dusk and evening, although a few are sometimes active on overcast days. On other plants the moths lay most eggs on leaves or, in corn, on green silk. On hemp, eggs are likely laid on the outer areas of the plant, particularly on younger leaves, such as those surrounding the flower buds and developing seed. Corn earworm moths lay their eggs singly (not in masses) which results in infestations being scattered through the crop. A female corn earworm may lay about 30 eggs each evening over the course of her lifetime, which typically lasts for about two weeks. Eggs hatch 2-3 days after being laid and the larvae begin to feed, usually concentrating on flowers and reproductive parts of the plant. The newly hatched caterpillars are minute, only about 2mm or so in length, but they develop quickly and are full-grown (about 25mm) in two to three weeks after eggs hatch, depending on temperature. Color of the caterpillars can be highly variable and can range from pale brown to nearly black, occur in various shades of green, or even may have reddish coloration. Most damage is done by the late stage caterpillars which are present 10-14 days after egg hatch and feed for a week or two before being full-grown. Often there will be granular-form fecal pellets (frass) left around the feeding site that can be used for diagnosing injury. The full-grown caterpillars will drop to the ground, enter the soil and create a small earthen cell a few inches below ground where they transform to the pupal stage. During the growing season, the adult will emerge about two weeks later and produce a new generation. Corn earworms that develop late in the season will produce a pupal stage that remains dormant until the following season. In areas and seasons where there is deep freezing of the soil these pupae are often killed. Warmer areas, or seasons that follow very mild winters, are likely to have high survival of pupae through winter.

Damage to hemp by corn earworm has potential to cause significant damage, particularly to the crops grown for production of large buds to extract CBD or other pharmaceutical compounds. The caterpillars burrow into the buds and cut stems, causing hemp wilting and death of tissues beyond the cut area. Late stage caterpillars can feed extensively and may damage multiple buds. Outbreaks are episodic, but some areas in the Arkansas Valley saw significant injury in 2016 and again in 2018. Potential damage to fiber or seed producing cultivars is likely to be much less than to CBD cultivars that produce large buds of unfertilized flowers. 

A Proposed Management Plan suggests regularly monitoring flights of the adult corn earworm after flowering and to consider treating fields with allowable formulations of insecticides when trap captures indicate high moth numbers, which are associated with egg laying. 

Eurasian Hemp Borer


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  Insects that Develop in the Roots  

Rice Root Aphid

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Fungus Gnats


Fungus gnats look like tiny dark flies. They hang around soil that stays wet for long periods of time, and their worm-like larvae crawl around in the wet top soil. Plants start getting sick if a gnat infestation gets out of control. Fungus gnats (Bradysia spp.) are small (1/8 inch), delicate, black flies with long legs and antennae. They are a common insect seen indoors, particularly in the winter and spring, usually in close proximity to potted plants. The adults are sometimes considered a nuisance, although they are short-lived (less than a week), cannot bite, and do not feed. The larvae are worm-like and translucent, with a black head capsule, and develop in soil/growing media. They primarily feed on fungi and algae but may incidentally chew smaller plant roots. Direct root damage from fungus gnats is usually minimal, but injured roots can be invaded by fungi that cause root decay. Fungus gnat larvae are usually located in the top 2-3 inches of growing medium, depending on moisture level, where they feed on fungi, algae, and decaying plant matter. They will feed on plant roots and sometimes on leaves resting on the growing medium surface. Larvae develop rapidly and are fully grown in 2 to 3 weeks. They then pupate in or on the growing medium surface. Adults emerge about a week later. Fungus gnat adults are weak fliers, typically flying in short, erratic patterns. In homes, they are commonly observed near the vicinity of and associated with the growing medium of houseplants; however, they may disperse short distances often accumulating around window frames. During their seven to 10 day life span females may lay up to 200 eggs into the cracks and crevices of growing media. At typical room temperatures (65 to 75ºF) the life cycle (egg to adult) may be completed in 3 to 4 weeks.


 Natural Predators of the above Pesty Insects 

Spined Assassin Bug

Assassin bugs are a well-named group of insects that develop by preying upon other insects. Three species of assassin bugs have been found in Colorado hemp. Most common is the spined assassin bug (Sinea diadema). Adults are about 1/2- inch long, making them about the largest of the insect predator one may find in Colorado hemp crops. They feed using piercing-sucking mouthparts, which appear as a “beak” curved along the underside of its head and they can feed on wide variety of insects. Spined assassin bug has been reported to favor as prey small bugs (e.g., Lygus bugs) and beetles. This assassin bug likely will also feed on the various caterpillars found on the crop, such as corn earworm, zebra caterpillar, and yellowstriped armyworm. Winter is spent as eggs, laid in the form of masses glued to plants. The first generation likely develops in off-field sites feeding on insects developing in weedy patches, fields, trees, and shrubs. Migration into hemp by adults that originating from these areas can later occur in early summer. The second, midsummer generation may develop in a wide variety of annual crops. The other assassin bug that occurs widely in hemp, but is never common, is Zelus tetracanthus, sometimes called the “fourspurred assassin bug”. It is about the same length as the spined assassin bug, but longer-bodied and darker. Adults only of this insect have been found in hemp so it may not reproduce in the crop.

Ambush Bug

Late in the season, in hemp that produces flowers, the ambush bug (Phymata americanum) may be present. Adults of these assassin bugs will rest near developing flowers and capture insects that visit the plant to collect pollen, including bees. Ambush bugs do not reproduce within the crop, no eggs or nymphs are present.


Big-eyed Bug

The big-eyed bug (Geocoris punctipes) is a generalist predator of insects and is a common resident of many cultivated crops grown in the region. It is a fairly small insect, only about 1/6-inch when full grown, generally grayish with a dark marking on the center of the back. Nymphs are smaller and lack wings. (Note: Several other Geocoris species occur in North America and many of these can be expected to be found in hemp.) The large eyes that extend from the sides of the head distinguish this insect from false chinch bugs, which are a plant feeding species. In hemp, these big-eyed bugs are likely feeding on aphids, nymphs of Lygus bugs and leafhoppers, young caterpillars and other small insects associated with the crop.


Damsel Bug

The damsel bug Nabis alternatus is the insect predator that has been most consistently found present in hemp in eastern Colorado. It is a generalist predator, associated with many crops, particularly alfalfa. In hemp it is likely feeding on aphids, nymphs of Lygus bugs and leafhoppers, young stages of caterpillars and other small insects associated with the crop. Reproduction within the crop does occur. Eggs are inserted into stems and nymphs hatch from the eggs in about 9 days. The immature stages closely resemble the adults in form, but are smaller and lack wings. A generation is completed in about a month so multiple generations may be produced during a growing cycle.


Minute Pirate Bug

The minute pirate bug (Orius insidiosus) is among the smallest of the predators of insects that occur in hemp, adults being 2- 3 mm in length. They can be among the most abundant, particularly in hemp fields with flowers, which are particularly important in development of populations of their primary prey, thrips. In addition to thrips, minute pirate bugs may also feed on spider mites and many of the smaller insects on the crop, such as aphids, and young stages of various bugs, caterpillars and beetle larvae. Although the winged adult insects are marked with conspicuous black and white patterning, the wingless immature stages (nymphs) are generally yellowish or yellowish-brown. Superficially they may resemble a small aphid, but they can be distinguished by being much more active in movement and by lacking the “tail-pipe” cornicles that extend from the abdomen of aphids.


Ragweed Plant Bug

Often found in sweep net collections of hemp is a small (ca 2mm) black plant bug, Chlamydatus associatus. Although known as the "ragweed plant bug" because of its common association with many weedy plants, it is not a plant feeder. It is a generalist predator, feeding on small insects such as aphids and thrips. Despite being regularly collected, breeding on hemp has not been confirmed as only adults have been recorded to date. It may be only a casual migrant or prove to do some limited reproduction within the crop.


Stilt Bug


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European Mantid

The European mantid (Mantis religiosa) is a generalist predator of insects that are actively moving on plants. In hemp, younger mantids present in late spring and early summer would likely find leafhoppers and small flies as typical prey. As the mantids mature larger insects are taken, such as grasshoppers, larger flies, bees, and beetles. Both green and brownish forms of this insect occur. All mantids have a one year life cycle. The overwintering stage are that are in a case and attached to rocks, stems and other solid surfaces during late summer and early fall. In fields that are tilled or have vegetation removed at the end of the growing season, egg masses are destroyed. As a result populations of mantids surviving (as eggs) between seasons will be in non-cultivated areas, such as field edges. Other mantids likely occur in hemp, although they have not yet been recorded. 


Twospotted Collops Beetle

Twospotted collops beetle (Collops bipunctatus) is a generalist predator of insects and is a common resident of many cultivated crops grown in the region. In hemp it is likely feeding on aphids, nymphs of Lygus bugs, young stages of caterpillars and other small insects associated with the crop. Pollen may supplement the diet of the adult beetles. Twospotted collops beetles can be found searching the crop throughout most of the season, and often are among the first insects one can easily observe in fields. Larval stages occur in soil and develop as predators of soil-dwelling insects. Both male and female adult insects are generally similar in appearance and size, but can be differentiated by the antennae, which are straight with the females and are distinctly enlarged at the base with the males.


Convergent Lady Beetle/Lady Beetles

Lady beetles are the most widely known of the kinds of insects that feed on other insects and/or mites (i.e., natural enemies, biological controls). Some 80 species of lady beetles are present across North America. Lady beetles develop through complete metamorphosis. This involves four life stages: egg, larva, pupa, and adult. All of these can be easily found on hemp. Lady beetles lay eggs, on the leaves and buds of hemp, which are in the form of a small mass. The eggs are usually yellow or orange-yellow, somewhat spindle-shaped, and each egg mass may contain from as few as 5 to over 50 eggs. Adult beetles will lay most all eggs on plants that provide abundant insect prey to support the young; cannabis aphid is a particularly important kind of prey for the lady beetles on hemp. The eggs will hatch in about a week after they are laid, but is dependent on temperature. The larvae that emerge from the egg are very small, about the size of the egg. They are generally dark gray and have legs that prominently stick out along the side of the body. Within hours after hatching, the larva begins to wander in search of prey. Over the course of the next 2-4 weeks (dependent on temperature) the developing larva grows in a series of stages, shedding its old “skin” in a process known as molting. As the larvae develop, they increase in size and most will develop spotting or other colored markings. The larval stage is entirely predatory and is the most important stage for controlling insect pests on the crop and each will consume hundreds of insects in the course of their development. The lady beetles found in hemp are generalist predators, which may feed on a wide variety of small, soft-bodied insects. Aphids are the primary food used by lady beetles and high numbers of these insects will only be found when high populations of cannabis aphid are present. The lady beetle larvae may also feed on other small insects such as leafhoppers, young Lygus bugs, small caterpillars and insect eggs. 

When the larva has consumed as much food as needed, it will begin the transformation to the next stage, the pupa. First they will settle somewhere on the plant, a leaf or stem, and attach to it at the end of their body. During the next day they remain in place, and their body shortens and thickens a bit. This is known as the “prepupa”. Later the old skin of the larva is shed, revealing the pupa. The pupal stage remains attached to the plant and is somewhat more rounded in form. The pupa is pale colored when first produced but within a day darkens and is colored orange or orange-red, with some black markings. Depending on temperature, this stage will last about 10-14 days and ultimately the adult form of the insect emerges. The adult is very pale and soft upon emergence from the pupa, but will darken and harden over the next several hours. When it is able to fly, it will usually leave the plant. The old “skin” of the pupa remains behind. Lady beetle adults feed on insects, but not as many as their younger stage larvae. Adult lady beetles will also feed on supplemental foods such as honeydew (sweet waste excreted by aphids) or pollen. The adults are long-lived, at least a couple of months, and those produced late in the season seek shelter where they will survive through winter. 


Green Lacewings

Green lacewings are some of the most commonly encountered, and most important, of the insects present in hemp fields that feed on other insects. The adult stage is most commonly seen, which have a generally green body and transparent wings that have many veins, producing a somewhat lacy appearancethat they fold roof-like over the body. The immature stage of all green lacewings develop as a predator of insects. Immature green lacewings, known as larvae, have an elongate body, tapered at the hind end. On the head are a pair of thin, curved jaws that they used to capture and feed on insect prey. Green lacewing larvae use these jaws to pierces their prey and then suck fluids from them. Known sometimes as “aphid lions” green lacewing larvae are voracious predators that not only feed on aphids, bud many other kinds of insect they encounter as they actively crawl about and search plants. They are capable of feeding on fairly large insects, including caterpillars many times their size. When full-grown, the larvae settle in a protected site and spin round-form cocoons within which they transform to the next stage, a pupa. Ultimately, either later that season or the following spring, the adult will emerge. Adult green lacewings may, or may not be predators of insects. Those in the genus Chrysopa, are predacious as adults, those in the genus Chrysoperla are not. All adult lacewings will feed on other foods, such as pollen, nectar and honeydew. Green lacewing adults lay eggs on leaves or other areas of plants on which prey are present that would support their young. Green lacewing eggs are unique in form, as they are laid on a stalk. Eggs may be laid singularly or in small groups. Three species of green lacewings have been regularly encountered in hemp fields. Most widespread in hemp fields is usually goldeneyed green lacewing (Chrysopa oculata) but two other species, Chrysopa nigricornis and Chrysoperla plorabunda, also occur in hemp fields. Some species of green lacewings are available commercially, reared in special facilities (insectaries). These are normally sold as eggs, mixed with some carrier (e.g, rice hulls) that are sprinkled on plants, or attached in group onto hang-cards. The primary commercial species sold is Chrysoperla rufilibris. Releases of these commercially available species have potential value to control some hemp insects, particularly cannabis aphid, on indoor plantings.


Longlegged Flies

Long-legged flies (Condylostylus species) are small metallic colored (green, bronze) flies that are seen resting on – or more commonly actively moving about upon the leaves of hemp. The adults are predators of many kinds of small insects that may occur on Hemp – aphids, leafhoppers, small midges, etc. Larvae of most long-legged flies develop as predators in soil and feed on other arthropods.


Flower Flies/Syrphid Flies

Adult stages of syrphid flies typically have yellow/orange and black markings creating an appearance that causes them to mimic/resemble bees or wasps. Known variously as “flower flies”, because they are often seen visiting flowers for nectar, or “hover flies”, because they can hover in flight, they are harmless and can neither bite nor sting. The nectar from flowers or the sweet honeydew excrement of aphids and related insects are the foods on which the flies feed. Adults lay their egg near colonies of aphids. Immature stages (larvae) of flower flies develop as predators of aphids. However, the larvae are infrequently observed on plants as they are legless, move slowly, and often have coloration (greens, grays) that blends well with the leaf surface.


Robber Flies

Robber flies are common insects of fields and rangelands that that hunt flying insects. They are large flies, many approaching an inch in length, with a very elongated body. Larvae of robber flies develop in soil. Most species of robber flies develop in off-field, non-cultivated sites and only adults move into cultivated fields to hunt prey.


Daddylonglegs

Daddylonglegs (Phalangium opilio) are very widespread, and a common resident of yards/gardens, pastures, and uncultivated areas alongside roads, ditches and fields. Being very active animals they will readily move into crops. Daddylonglegs will feed as a predator of many kinds of insects associated with hemp – aphids, caterpillars, leafhoppers. They also will feed as scavengers, on recently dead insects and earthworms. Daddylonglegs can be seen moving about during the day, but they are most active at night and spend most of the day resting on foliage. They produce at least two generations annually. Stages surviving through winter may include a mixture of eggs, immature nymphs, and adults. The eggs are laid in cracks of moist soil, with most egg laying usually occurring in late summer and early autumn when the adults are most abundant.


Spiders

Spiders are predators of insects and other arthropods and are often very important in managing pesty insects in agricultural crops. Numerous kinds of spiders have been found associated with hemp fields, and several likely contribute to suppressing several pesty insects on hemp, including various caterpillars, young stages of stink bugs and Lygus bugs, aphids, and other insects. Most consistently found are crab spiders in the genus Mecaphasa. These are ambush hunters that lie in wait on the leaves and the stems of plants, waiting for prey to pass close by. Crab spiders can be distinguished by their having the front two pair of legs being considerably longer than the hind pair. Fairly similar in appearance, and also possessing elongated front legs, are running crab spiders, mostly in the genus Philodromus. These are usually a bit larger than crab spiders but are much more active and can run quite quickly. Several species of jumping spiders may also occur in hemp. These are very active hunters with excellent vision. They are capable of stalking and can make short jumps to pounce upon and overcome their insect prey. None of the above kinds of spiders use silk for prey capture. They do use silk for other purposes, such as in production of egg sacs and for a dragline laid down so that they can drop safely off a plant. Perhaps the most commonly seen silken structures on hemp plants, other than webs, are retreats constructed by spiders for shelter. 

Pollinators

Hemp Pollen and Bees

Enormous amounts of pollen can be produced within hemp crops grown for seed or otherwise include pollen-producing male flowers. This makes the crop very attractive to bees - honey bees, bumble bees and many kinds of solitary bees. Pollen is a critically important food resource for these bees, and is used mostly for rearing their young. Pollen-producing hemp crops likely can provide substantial benefits to bees. This will be particularly important in areas where there are few other pollen sources available in mid-late summer when hemp is flowering.

Bee diversity and abundance on flowers of industrial hemp (Cannabis sativa L.) By: C. O’Brien and H.S.Arathi at Colorado State University

Industrial hemp is one of the earliest crops spun for fiber, and is now used for a variety of commercial products including paper, textiles, clothing, biodegradable plastics, biofuel, food, animal feed etc., which are all derived from hemp fiber or seeds. Being wind pollinated, dioecious and staminate , industrial hemp plants produce large amounts of pollen that are attractive to bees. Hemp flowering occurs between the end of July and the end of September. This time period coincides with a dearth of pollinator-friendly crop plants, making industrial hemp flowers a potentially valuable source of pollen for foraging bees. While hemp does not produce any nectar, the pollen rich nature of the flowers can make hemp an ecologically valuable crop. As cultivation of hemp continues to expand, we expect insect pests on hemp to also become prevalent. 


  Incidental Species Commonly Observed on Outdoor-grown Hemp  

Bumble Flower Beetle

Adults of the bumble flower beetle (Euphoria inda) are fairly large, slightly hairy beetles that are present in mid to late-summer. They are scavengers, most often observed at flowers (e.g., daylilies, large thistles) or visiting fermenting fruit. In hemp they have been observed to visit frothy ooze resulting from bacterial infection of wounded stalks; fermenting pollen may also be eaten. Larvae of the bumble flower beetles are a type of white grub that develops in animal manure or compost.


Flesh Fly



Midge



Golden Tortoise Beetle

Some of the more strikingly colored insects that may be found around hemp fields are the "golden tortoise beetles". A “gold bug” or “golden lady bug” are common descriptions of someone first seeing one of the golden colored tortoise beetles. They have a generally rounded body form and a similar size to some common lady beetles (about 5-6 mm length). Their body is domed, with somewhat flatter areas along the edges, somewhat resembling a safari hat. When disturbed they can press themselves close to the leaf surface with all appendages safely protected underneath, somewhat in the manner a tortoise can withdraw into its shell. Despite their resemblance to a lady beetle, tortoise beetles have very different habits and feed on leaves of plants. Those most commonly found feed on field bindweed and other plants in the morning glory family. Their presence in a hemp field results from the presence of field bindweed or other host plants; these insects do not feed on hemp. Evidence of these insects is the appearance of small, roundish holes in the interior of the leaves of bindweed. These are chewing injuries that are produced by both adult and larval stages. The larvae of field bindweed are much less commonly noticed than are the adults, being slow moving and occurring on the underside of leaves. A distinctive feature of the larvae is that they often carry a covering of old feces and discarded skins, which is attached at the end of the body and provides a shield over the back. 


Purslane Blotchmine Sawfly

The purslane blotchmine sawfly (Schizocerella pilicornis) can be a commonly noticed insect in hemp fields where the weed purslane is abundant. Adults are small (about ½-in) dark colored non-stinging wasps that rest on the foliage of all kinds of plants. Purslane is the only host of this insect. Females insert their eggs on the edge of a purslane leaf, usually laying only a single egg per leaf. Upon hatch from the egg, which occurs about 3-4 days later, the larva then feeds internally in the leaf, ultimately excavating a blotchy leaf mine. The larvae will complete development within 5-6 days, then exit the leaf to burrow into the soil. It moves about an inch deep, where it makes a small chamber where it transforms to the pupal stage, which occurs within a tough, silken cocoon. Pupation last about 7-10 days, after which a new adult emerges from the pupa, cutting its way through the cocoon and digging to the soil surface. Females are somewhat larger than males and males have antennae that is branched. Upon mating females will begin laying almost immediately. Several dozen eggs may be laid, almost all on the same day the adults emerge and mate. Adults usually live only a single day. There can be multiple generations produced per year. Late in the season the larvae will go into dormancy within the cocoon, suspending development until the following spring.