Insects and Mites Associated With Hemp Production

Hemp fields can support a lot of different kinds of insects. Being able to recognize what is present – and also what they may be doing to the crop – is a fundamental interest of any producer.

Some of the insects one will see may be feeding on the plant, either chewing leaves or flowers, boring into seed heads or stems, or sucking fluids from leaves. Also common, and sometimes more visible, are various insects and spiders that feed on other insects, the natural enemies of those that feed on the plant. Hemp may be used as a temporary site for resting and shade by various types of “transient” insects that are locally common and hemp crops that produce pollen can attract enormous numbers of bees and other pollen feeders.

This website seeks to illustrate all of the “bugs” (insects, spiders, mites, etc.) one might encounter in a hemp field, providing a type of diagnostic guide. With this information growers can better understand what they are observing in production of this crop and be able to appropriately respond.

In this start-up form (spring 2017), the Hemp Insect Website has a particular focus on what is known to occur in Colorado, as preliminary surveys have been made in this state in 2015-2016. However, as the goal of this website is to provide progressively more comprehensive treatment of insects associated with hemp production throughout the United States. One way that this is being encouraged is by providing a means to submit images and inquiries of insects that are observed on any US-grown hemp, to do so please see the “Got Bugs?” page.

Beet Webworm

The beet webworm (Loxostege sticticalis) is a caterpillar that reaches moderately large size when full grown (ca. ¾ inch) is generally green and marked with striping and white spots that have a black center. They will typically be found feeding amongst emerging leaves and around buds, usually within some loose silken webbing that produces a shelter for the insect and may tie together some leaves.
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. When mature, larvae drop to the soil and pupate.
Adults emerge in about a two weeks and produce a second generation. 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.
Lepidoptera: Crambidae

Beet Webworm

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.

Lepidoptera: Noctuidae

Grasshoppers

There are well over 100 species of grasshoppers that occur in Colorado and the western states. Specific grasshopper species that have been documented to date that feed on hemp in Colorado include differential grasshopper (Melanoplus differentialis) , Lakin grasshopper (Melanoplus lakinus) , and Russian thistle grasshopper (Aeoloplides turnbulli).

Grasshoppers chew leaves and may gnaw on stems of hemp. Where grasshopper populations are high leaf chewing injuries can significantly affect crop growth Hemp is likely most susceptible to grasshopper injury when plants are small during establishment, which can retard growth and even kill plants in extreme situations. However, hemp has good ability to tolerate leaf loss and moderate levels of grasshopper defoliation likely have no effect on yield. Damage to growing points of plants or gnawing of stems, which can cause stem breakage, may cause more important injuries by distorting plant growth.

All grasshoppers associated with hemp have a life cycle that takes one year to complete. Eggsh are laid shallowly in soil, in the form of pods, each containing a couple of dozen eggs, during late summer. This is the life stage that survives between growing seasons and grasshopper 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 may allow eggs, and later hatching nymphs, to survive and develop throughout the field.

Orthoptera: Acrididae

Differential Grasshopper (Melanoplus differentialis)

Lakin Grasshopper (Melanoplus lakinus)

Russian thistle Grasshopper (Aeoloplides turnbulli)

Southern Corn Rootworm

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 is often barely observable. It is unlikely that the larvae will develop on hemp roots.

Coleoptera: Chrysomelidae

Flea Beetles

Flea beetles are tiny beetles that have enlarged hind legs that allow them to jump. Two species of flea beetles have been recorded from hemp in Colorado, the western black flea beetle (Phyllotreta pusilla) and the palestriped flea beetle (Systena blanda). Damage produced by both species is done by the adult beetle, 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.

The western black flea beetle is the smaller of the two, about 1/10-inch long, with a shiny dark body. Adults may be expected to be seen in hemp early in the season (June, early July) then again in late August and September. This insect has a very wide host range but develops in highest numbers in mustard family plants and it is a key pest of crops such as canola, cabbage, and broccoli. Many common weeds, such as flixweed and tansy mustard, are important in providing food plants that sustain the first generation of western black flea beetle.

The palestriped flea beetle is a bit larger, about 1/6-inch long, and marked with yellowish stripes along the back. It also has a very large number of crops on which the adults will feed, including lettuce, beans, potato, and sunflower.

The larvae of both of these flea beetles develop feeding on roots of plants. However, the injury this stage (larva) produces is generally considered to be negligible to 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.

Another species of flea beetle, 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. To date, this insect has not been observed in hemp grown in Colorado.

The potential of these insects to significantly damage hemp would 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.

Coleoptera: Chrysomelidae (Alticinae)

Yellow Woollybear

The term “woollybear” is given to certain densely haired caterpillars that wander considerably between plants. Also, they are usually observed in late summer and early autumn, which is when they occur on hemp. Two species of woollybears may be found on the crop, the yellow woollybear (Spilosoma virginica) and the saltmarsh caterpillar (Estigmene acrea).

Caterpillars of yellow woollybear are densely hairy and pale colored – ranging from light brown, to yellow to nearly white. The adult moths are moderate size with a wing span of 3.8-5.0 mm. The forewings are white with black spotting. Female moths have white wings with a small dark spot in the center.

The yellow woollybear survives winter as a pupa within a cocoon, hidden amongst leaves and other plant debris on the soil surface. Adults emerge over an extended period in spring and, 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 egg hatch the tiny, 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 and repeat the cycle. 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.

Lepidoptera: Noctuidae

Saltmarsh Caterpillar

Saltmarsh caterpillar is an insect that occurs throughout much of the United States and is present throughout Colorado, except at the highest elevations. It is commonly encountered on a wide variety of plants, but serious damage on any crops are rare.

Caterpillars of saltmarsh caterpillar are densely hairy. Younger stages tend to be predominantly yellowish, but as they age they darken. However, there is wide variation on coloration 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 orange abdomen. Males have white hind wings and an abdomen tipped with white.

The saltmarsh caterpillar survives 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.

Upon egg hatch the caterpillars originally feed as a group, producing skeletonizing injuries to 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. The rather unusual name for the caterpillars is derived from their occurrence as a pest of gardens New England settlers that were located in salt marsh areas.

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, sometimes 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.

Lepidoptera: Noctuidae

Painted Lady

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. As they age they become variably marked with black and yellow, with considerable range in the overall coloration.

The caterpillars have a wide range of food hosts but primarily feed on plants in the families Asteraceae (Compositae), Boraginaceae, and Malvaceae. Various thistles are particularly common hosts and the name “thistle caterpillar” is sometimes given to this species. During outbreak years the caterpillars may extensively defoliate thistle in late spring, sometime then wandering in large numbers in search of new host plants.

The adult painted lady is a large butterfly marked predominantly with orange and black. It is a highly migratory species that is almost constantly in motion. During 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.

Peak feeding by painted lady caterpillars typically is most common in early summer, following the annual migration of the adults into the state. Damage to hemp is limited to foliage and the populations of caterpillars almost never reach sustained high numbers due to the presence of abundant natural controls. Furthermore, significant weeds, notably Canada thistle, are even more preferred and are far more likely to be significantly damaged than is hemp. Damage to hemp by caterpillars of the painted lady can sometimes be visible, due to the leaf tying, but effects on crop growth and yield are likely to be minimal and insignificant.

Lepidoptera: Nymphalidae

Cotton Square Borer

The larvae of cotton square borer (Strymon melinus) are pale green (sometimes brownish), fuzzy caterpillars that may reach about ½-inch length when full grown. Adults are an 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 in Colorado.

Damage to hemp by this insect is likely to be minimal and insignificant. This insect is never abundant and largely feeds on foliage. Some bud tunneling may occur, although it has not yet been documented.

Lepidoptera: Lycaenidae

Zebra Caterpillar

The Zebra caterpillar (Melanchra picta) is a very strikingly colored caterpillar, generally black with white markings and yellow striping. It will develop feeding on the foliage of a wide variety of plants, particularly those in the mustard family, but has been found in low numbers on hemp in several locations, usually in late summer.

Peak feeding occurs late in the season, is limited to foliage and the numbers of zebra caterpillars are consistently low due to high levels of natural controls effectively suppressing their populations.

Damage to hemp by zebra caterpillar can be expected to be minimal and insignificant to crop yield .

Lepidoptera: Noctuidae

Insects/Mites that Suck Fluids from Leaves

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Leafhoppers

Leafhoppers 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 quite actively crawl on plants. The leafhoppers associated with hemp are poorly studied at present but adults of at least three species have been commonly found on the crop in Colorado. It is likely that many leafhoppers found on hemp do not reproduce on the crop, and those that do occur consist only of adults that have moved from other plants on which they breed.

Leafhoppers feed on leaves and stems with piercing sucking mouthparts that extract a bit of fluid from the plant. Most feed on the phloem of plants, resulting in insignificant effects on plant growth and produce no visible symptoms. A few leafhoppers feed on the mesophyll and a small, light flecking injury may occur at the feeding site. And although some leafhoppers are known to transmit plant pathogens that cause diseases of crops (e.g., aster leafhopper and the phytoplasma that produces aster yellows) none of these leafhopper-vectored plant diseases are presently known to affect hemp. In summary, it is unlikely that leafhoppers will be a significant pest of the crop under any circumstances.

Hemiptera: Cicadellidae

False Chinch Bugs

False chinch bug (Nysius raphanus) is one of the most commonly encountered plant feeding insects in much of Colorado. They can be found on 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 summer.

It can be expected that some false chinch bugs will be found in hemp throughout the growing season. However, occurrence of noticeably large numbers likely will only occur if large areas of winter annual mustards in near vicinity are cut or rapidly dry down, forcing migration of the insects.

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 and it can be expected that measurable damage to hemp by false chinch bugs would only occur when extremely high populations occur on plants for a period of many days-weeks. The damage that false chinch bugs may produce to hemp has little potential to cause effects on yield.

Hemiptera: Lygaeidae

Lygus Bugs

Lygus bug is the name given to a group of plant bugs in the genus Lygus that are very commonly found in crops, gardens and natural areas throughout the state. Several species occur in Colorado; to date the most common species found in hemp in eastern Colorado is the pale legume bug (Lygus elisus). Two other species found in most any crop grown in the region are the western plant bug (Lygus hesperus) and the tarnished plant bug (Lygus lineolaris).

There are hundreds of plant species on which Lygus 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 in Colorado, 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 that 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. However, they have been important in 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.

Hemiptera: Miridae

Red-shouldered Stink Bug

The redshouldered stink bug Thyanta custator is one of the larger and more conspicuous insects one might see on hemp plants, almost ½-inch in length with a broad body form. Most often they are pale green but there is considerable variation in color, with some having more brownish coloration. A faint red band often is present across the body in the area behind the head.

Redshouldered stink bug feeds on many kinds of plants and can be common in wheat, beans and alfalfa. They feed with piercing-sucking mouthparts on young leaves, flowers and developing seed but appear to cause little injury; injuries this insect are reported to cause involve seed production. Migrations of adult insects into hemp may occur in midsummer as small grains and weedy hosts mature and the redshouldered stink bugs will most always be noticed around buds and developing seeds.

Damage to hemp by redshouldered bug is likely to be minimal to 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.

Hemiptera: Pentatomidae

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. Egg laying 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 typically remain clustered about the eggs for a few days, before dispersing. It takes about between 35-60 days after egg hatch for the developing nymphs to reach the adult stage. The nymphs are smaller than the adults, have a somewhat more rounded body form and lack wings, so their abdomen is exposed. The adult insects continue to feed into fall, ultimately moving to sheltered sites to survive winter. Life history is generally similar with both species but Say’s stink bug may produce two or more generations per season and the conchuela only produces a single generation.

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. As these stink bugs are unlikely to ever become very abundant in fields, concentrate along field edges when they do occur, and cause minimal injury, largely related to seeds, they should be only minor pests of the crop.

Hemiptera: Pentatomidae

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 are a minor component of the natural enemy complex within hemp. They may also occasionally drink fluids from plant with their piercing-sucking mouth parts, but such feeding would not produce any effects on hemp plants.

Hemiptera: Berytidae

Thrips

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 twospotted 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. To date, only onion thrips have been recorded in Colorado from indoor-grown hemp. However, western flower thrips is a well known pest of many greenhouse crops grown in the state and likely also is present on some indoor grown crops. Both onion thrips and western flower thrips are among the most common and widely distributed insects that occur in Colorado. Both have a very wide host range of plants on which they can develop.

Click “Thrips” in gold above and read more on our Thrips PDF file.

Thysanoptera: Thripidae

Thrips: Pest Management of Hemp in Enclosed Production

Cannabis Aphid

Cannabis aphid (Phorodon cannabis) is found on the leaves and stems of Cannabis. Overall coloration can be variable; pale yellowish forms are common, particularly indoors, but forms that are darker green and pale brown occur. Cannabis is the only known host of this aphid. Presumably it is normally sustained through winter on indoor grown plants. Overwintering plants located in protected sites may also be potential outdoor hosts between growing seasons.

Cannabis aphid, and other aphids, suck fluids from the phloem of the plant. In high populations this can result in reduced growth and wilting, although plants that are well hydrated can well tolerate this type of injury. In outdoor plantings there are normally numerous natural enemies (e.g., lady beetles, flower flies, green lacewings, parasitic wasps) that limit aphids, of all species, to levels that do not produce significant plant injury. In indoor planting these natural enemies are normally not present, unless introduced.

Cannabis aphid is very similar in appearance to hop aphid, Phorodon humuli, and can only be distinguish by closely examining, under a microscope the area at the front of the head. Hop aphid is a common species found on hops in North America and it is also reported to develop on Cannabis. Hop aphid has a life cycle that involves alternating between different host plants through the year, with certain Prunus species(cherries, plums) serving as the hosts on which it survives (as an egg stage) between outdoor growing seasons. Green peach aphid (Myzus persicae) and bean aphid (Aphis fabae) are among the other aphids that have been reported as feeding on hemp, but these have not yet been confirmed from hemp in Colorado.

Hemiptera: Aphididae

Cannabis Aphid: Pest Management of Hemp in Enclosed Production

Rice Root Aphid

Rice root aphid (Rhopalosiphum rufiabdominalis) is a dark olive-green insect with a generally round body form. Wingless stages develop on roots and they survive on plants grown both in soil and in hydroponic culture. Winged stages periodically emerge from soil to fly to new plants; these are most often observed when they have been trapped by the hairs on the upper surfaces of leaves.

Rice root aphid has so far only been found associated with indoor Cannabis production. However, rice root aphid is well-known as an aphid that can be found year-round outdoors in much of North America. This aphid hasa 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 aphid; winged forms of this may enter vents and other openings.

Year-round reproduction can occur within indoor growing facilities growing hemp. 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 730F, an optimal temperature, rice root aphid populations can double every 1.6 days.

Hemiptera: Aphididae

Rice Root Aphid: Pest Management of Hemp in Enclosed Production

Twospotted spider mite

The twospotted spider mite (Tetranychus urticae)¹ mite is the most damaging spider mite species in Colorado. 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 adult twospotted 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, twospotted spider mites can survive 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 orange-red, 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 temperature and suitable light/dark periods (greater than 10 hours of light), such as occur with indoor production, twospotted spider mite will not undergo a dormant period.

Twospotted spider mite is probably the most important arthropod pest of 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) twospotted spider mite is likely to rarely, if ever, cause insignificant injury to the crop.

¹ Acari: Tetranychidae

Twospotted Spider Mite: Pest Management of Hemp in Enclosed Production

Hemp Russet Mite

Hemp russet mite (Aculops cannibicola) is extremely small – much smaller than the twospotted spider mite – and cannot be observed without some magnification (15-20X). They have an elongate body and pale color, typical of most eriophyid mites (the mite family Eriophyidae). During heavy infestations flowering structures may take on a beige appearance, the combined result of leaf injuries and the color of the mites observed when as the mass on the heads.
The biology of hemp russet mite is very little studied but is likely similar to related species of leaf-dwelling (rust/russet) eriophyid mites, such as tomato russet mite (Aculops lycopersici). It reproduces by production of eggs that, upon hatch, is followed by two immature stages (protonymph, deutonymph), followed by an adult. The entire life cycle (initially laid egg through first egg laying by the adult) of the tomato russet mite is reportedly completed in about a month at temperatures of 770F. Each adult will produce from 10-50 eggs.
Cannabis is the only known host for hemp russet mite and similar rust mites (e.g., tomato russet mite) do not produce any resistant stages. Therefore, nymphs and adults off the host are unlikely to survive for more than a few days to a couple of weeks, at the most. On their own, hemp russet mites can crawl only very short distances. However, they are readily carried on air currents and fans will quickly spread mites in enclosed areas. Some hemp russet mites may also be transferred from plant to plant on hands and clothing.
Initial signs of infestation are subtle and easily missed. They can also vary among cultivars. A slightly curling along the edges of leaves is the most common symptom observed, but this is not expressed in all plants. Others respond to having a general dullness of leaves (russetting). As infestations progress areas of leaves may have visible yellow or brown spotting. Foliage also may become brittle foliage, often resulting
Hemp russet mite is similar in appearance to the eriophyid mite illustrated above (wheat curl mite) Photograph courtesy of David Shetlar, The Ohio State University.
A slight rolling along the leaf edge is a symptom of infestation by hemp russet mite.
in breaks at the leaf petiole. Ultimately, highest populations usually occur on developing buds, which results in buds that are smaller and of reduced quality.
Hemp russet mite has only been observed associated with indoor-grown Cannabis that is propagated by cuttings, conditions that continuously provide live plants that can sustain it. Hemp russet mite is unlikely to cause significant injury to outdoor grown at sites where there are extended periods of cold and without live hemp plants.

Acari: Eriophyidae

Below are links to additional images of hemp russet mite.

There two excellent images by Karl Hillig of hemp russet mite and the leaf rolling symptom it produces.

These are posted at BugGuide.Net and are copyrighted but can be seen at:

Hemp Russet Mite Photo by Karl Hillig #1

Hemp Russet Mite Photo by Karl Hillig #2

Hemp Russet Mite: Pest Management of Hemp in Enclosed Production

Insects that Tunnel into Stems/Branches

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Eurasian Hemp Borer

Caterpillars of the Eurasian hemp moth (Grapholita delineana) feed on the upper canopy and terminal growth of plants. They may develop on leaves, flowers and developing seeds, but also bore into petioles and stems. This latter habit leads to them sometimes being known as hemp borer. The caterpillars are quite small, reaching a maximum size of about 6-8 mm, and have orange coloration. (Note: This is much smaller than the other common stalk boring caterpillar that can occur in hemp, European corn borer, which is light brown or cream colored and is much larger in size.)

The stage that survives through winter is a full-grown larva that will pupate the following spring. Outdoors this may occur within a folds of leaves and seed heads or within stalks and stems debris left in fields. However, this insect can also be brought indoors on seed heads and buds in storage or in stems cut from fields in late season used for propagation

Pupation may occur within stems, on leaves or amongst seed heads. Adults will emerge in late spring. Larvae that hatch from eggs of these moths will initially feed on the leaves, producing a minor skeletonizing leaf damage. They later bore into petioles and stems, where they complete development and pupate. A second generation of moths will emerge in midsummer.

The caterpillars from this second generation may cause more extensive injuries, feeding on terminal growth including flowers and developing seeds. These injuries can continue in storage after harvest. Some larvae will tunnel into stems, which can result in stem breakage.

The Eurasian hemp moth does have potential to be a significant insect pest of this crop, particularly of crops grown for pharmaceutical purposes (e.g., CBD) and seed. It also will likely become more commonly encountered in the crop as hemp cultivation expands.

Lepidoptera: Tortricidae

European Corn Borer

European corn borer (Ostrinia nubilalis) is an insect that commonly occurs through the Corn Belt and in the eastern U.S.; presently it is not present west of the Rocky Mountains. In Colorado it is particularly abundant in the northeastern counties.

The developing stages (larvae/caterpillars) of the European corn borer develop as a stem/stalk borer. In addition to corn a great many plants are hosts of this insect, including pepper, snap bean, 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, European corn borer was 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.

European corn borer spends winter in the stage of a full-grown larva within plant debris it fed upon during late summer/early fall. Pupation occurs in spring, and the adults emerge in late spring. Adults typically aggregate and mate in dense grassy “action sites”, then females lay eggs in the form of masses on 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, European corn borer has potential to be a significant insect pest of this crop. Stem and stalk tunneling may reduce yield and can also cause structural weakening that can cause stem/stalk breakage.

Lepidoptera: Crambidae

Insects/Mites associated with Buds/Flowers/Seeds

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Lygus Bugs

Hemiptera: Miridae

Red-shouldered Stink Bug

Hemiptera: Pentatomidae

Conchuela and Say’s Stink Bug

Hemiptera: Pentatomidae

Corn Earworm

The corn earworm (Helicoverpa zea) is one of the most commonly damaging insects of both field crops and vegetable crops in North America, known variously as the corn earworm (when in corn) the tomato fruitworm (when feeding on fruits of peppers, tomatoes, etc.) and bollworm (when feeding on cotton bolls). In hemp they feed on buds and developing seeds. Larvae carried on harvested plants will continue to feed and develop as plants dry.

In Colorado populations of this insect vary greatly from season to season and peak in late August and September. Damage to hemp by corn earworm has potential to cause significant damage, particularly to crops grown for production of large buds to extract CBD or other pharmaceutical compounds. Potential damage to fiber or seed producing cultivars is likely to be minimal.

Lepidoptera: Noctuidae

Proposed Management Plan for Corn Earworm in Hemp

Eurasian Hemp Borer

Adults will emerge in late spring. Images of the adult stage can viewed at http://bugguide.net/node/view/393718 Larvae that hatch from eggs of these moths will initially feed on the leaves, producing a minor skeletonizing leaf damage. They later bore into petioles and stems, where they complete development and pupate. A second generation of moths will emerge in midsummer.

Lepidoptera: Tortricidae

Insects that Develop in the Roots

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Rice Root Aphid

Rice root aphids (Rhopalosiphum rufiabdominalis) have so far only been found associated with indoor Cannabis production but are present year-round outdoors in much of North America. Rice root 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 aphid; winged forms of this may enter vents and other openings. Year-round reproduction can occur within indoor facilities.

Rice root aphid is dark olive-green insects with a generally round body form. Wingless stages would be observed belowground, feeding on roots. Winged stages periodically emerge from soil to fly to new plants; these are most often observed when they have been trapped by the hairs on the upper surfaces of leaves.

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 73⁰F, an optimal temperature, rice root aphid populations can double every 1.6 days.

Hemiptera: Aphididae

Rice Root Aphid: Pest Management of Hemp in Enclosed Production

Fungus Gnats

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 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. Moist growing media composed of peat moss are particularly attractive to adult females. At typical room temperatures (65 to 75ºF) the life cycle (egg to adult) may be completed in 3 to 4 weeks.

Diptera: Sciaridae

Fungus Gnats: Pest Management of Hemp in Enclosed Production

Natural Enemies of Insects/Mites associated with Hemp

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Spined Assassin Bug

The spined assassin bug (Sinea diadema) is perhaps the largest insect predator that one may find in Colorado hemp crops, although it is not commonly encountered. Using piercing-sucking mouthparts it feeds on wide variety of insects, but has been reported to favor small bugs (e.g., Lygus bugs) and beetles.

It is unlikely that this insect will reproduce within hemp fields. Winter is spent as eggs, laid in the form of masses glued to plants and the first generation likely develops in sites where there are perennial plants, including shrubs and trees. Migration into hemp by adults from these off-field sites then occurs in early summer. However, the spined assassin bug does produce two generations a year and reproduction within the growing hemp crop potentially could occur.

Hemiptera: Reduviidae

Ambush Bug

Adults of the ambush bug (Phymata americana) move into hemp in late summer and establish near flowers. The ambush bug is a predator that hunts by ambush, waiting for a suitable passing insect – often a bee or a fly – that it then grasps with its forelegs and incapacitates with a paralyzing saliva that it injects.

It is unlikely that this insect reproduces within the hemp crop as the surviving stage between seasons are eggs laid as masses, usually on trees, shrubs and other perennial plants. Although predatory, ambush bugs likely feed rarely on insects that may be considered plant feeding pests of the hemp, instead consuming transient species that rest on the crop or visit for pollen.

Hemiptera: Reduviidae

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 big-eyed bugs are likely feeding on aphids, nymphs of Lygus bugs and leafhoppers, young caterpillars and other small insects associated with the crop.

Hemiptera: Lygaeidae

Damsel Bug

The damsel bug (Nabis alternatus) is perhaps the insect predator that has been most consistently found present in hemp. 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.

Hemiptera: Nabidae

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. Instead 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.

Hemiptera: Miridae

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 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.

Hemiptera: Berytidae

European Mantid (Praying 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.

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. In southeastern Colorado a common species found along field edges of many crops is the Carolina mantid (Stagmomantis carolinensis).

Mantodea: Mantidae

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.

Coleoptera: Melyridae

Convergent Lady Beetle

The convergent lady beetle (Hippodamia convergens) is often the insect predator that is most commonly noted in hemp. One of about 80 species of lady beetles found in Colorado this native insect can be found in almost any crop grown in the state.

The stage that survives winter is the adult “ladybug” form, which become active in late spring. Where they find sources of food for their young – typically colonies of aphids – they will lay eggs. The eggs, laid on leaves and stems in the form of small masses (ca. 5-30), are yellow and spindle-shaped. The larvae that hatch from the eggs are grayish with prominent eggs and they search plants for prey. Later stage larvae are often marked with yellow or orange and may have purplish background colors.

The larvae are generalist predators that feed on small insects such as aphids, leafhopper nymphs, plant bugs, and young larvae of caterpillars or beetles. Through most of the growing season all stages of this insect may be present (eggs, larvae, pupae, adults) although the highly visible adults are usually the only stage one may notice in the crop.

The multicolored Asian lady beetle (Harmonia axyridis) and the sevenspotted lady beetle (Coccinella septempunctata) have also been observed to develop within hemp fields when large numbers of aphids are present.

Coleoptera: Coccinellidae

Green Lacewings

The goldeneyed green lacewing (Chrysopa oculata) is has been regularly found in hemp fields, most often in association with aphid infestations. (Several other species of green lacewings in the genera Chrysopa and Chrysoperla are associated with other agricultural crops within the region and it is likely that future sampling will identify that some of these also occur within hemp.) Both the larvae and the adults of the goldeneyed green lacewing are generalist predators that feed on small insects such as aphids, leafhopper nymphs, plant bugs, and young larvae of caterpillars or beetles.

The adult is an insect of fairly delicate features, with clear wings that are held roof-like over the pale green body when not in flight. Eggs are laid on leaves and the eggs are of unique appearance, produced at the tip of a stalk that is nearly ½ inch long. Eggs hatch in about 5 to 6 days and the larvae that emerge then crawl about the plant in search of prey. Green lacewing larvae are somewhat similar in general body form to larvae of lady beetles, but are distinguished by having long, curved mouthparts that project from the head and an abdomen that becomes more pointed at the end.

The lacewing larva will feed and develop over the course of 2 to 3 weeks, then settle in some protected site on the plant where it will spin a cocoon of oval form, and then pupate within the cocoon. In summer, an adult will emerge about a month later and produce another generation; lacewings developing late in the year will remain within the cocoon through the winter.

Neuroptera: Chrysopidae

Long-legged 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 – leaves of hemp. Adults are predators of many kinds of small insects that may occur on the crop – aphids, leafhoppers, small midges, etc. Larvae of most long-legged flies develop as predators in soil and feed on other arthropods.

Diptera: Dolichopodidae

Syrphid Flies (Flower Flies, Hover 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.

Diptera: Syrphidae

Robber Flies

Robber flies are common insects of fields and rangelands that that hunt flying insects. They are large flies, many approaching and some even exceeding an inch in length, with a very elongated body. In and around fields of crops grown in eastern Colorado species in the genus Proctocanthus, Efferia, and Diogmites are most often encountered.

Larvae of robber flies develop in soil. At least one common species in eastern Colorado, Diogmites angustipennis, is well adapted to developing in cultivated crops. Most species of robber flies develop in off-field, non-cultivated sites and only adults move into cultivated fields to hunt prey.

Diptera: Asilidae

Daddylonglegs

The daddylongleg, Phalangium opilio, is very widespread in Colorado 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.

Phalangium opilio probably produces two generations annually in Colorado. 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.

Opiliones: Phalangiidae

Spiders

Spiders are very important natural enemies of plant feeding insects in all cropping systems.

To date, the specific types of spiders that are present in hemp crops have not been described; undoubtably, spiders are among the most important natural enemies of insects that occur on hemp, particularly in outdoor plantings. Spiders observed in hemp to date include species in at least four spider families: Thomisidae/Crab Spiders, Salticidae:/Jumping Spiders, Oxypodidae/Lynx Spiders, and Araneidae/Orbweaver Spiders).

Further identification of spiders that are important in hemp crops is a project goal for the Hemp Insect Web Site Project and will be a focus of attention in 2017.

Araneae: Thomisidae, Salticidae, Araneidae, Oxypodidae, others

Incidental Species Commonly Observed on Outdoor-grown Hemp

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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.

Coleoptera: Scarabaeidae

Physiphora demandata

Physiphora demandata is a moderate-sized (ca. ¼-inch), shiny metallic green fly that may be seen sunning on leaves of hemp. It does not feed on the crop but apparently moves to the plants from off-field areas as a site where adults aggregate and mate. Mating pairs are sometimes noticed and the flies engage in mating dances of rather peculiar appearance, involving much waving of the front legs.

Larvae of this fly develop in decaying plant and animal materials, including manure. Adults may suck water and other available fluids but do not damage plants.

Diptera: Ulidiidae

Hemp Pollen and Bees

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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 as a critically important food resource for these bees, and is used mostly for rearing young. Pollen-producing hemp crops likely can provide substantial benefit to bees. This will be particularly important in areas where there are few other pollen sources are available in mid-late summer when the crop is flowering.