Reportedly there are well over two hundred and fifty insects and mites associated with Cannabis. I think it is best to talk about those that have the most economic impact.
These arachnids are the most destructive pests of greenhouses (glasshouse) and grow rooms. Often growrooms are contaminated because infested “clones” are brought in. Outdoor crops may also become infested in warm climates. Mites just love hot, dry, dusty environments. Spider mites bite leaves and suck up exuded sap. They congregate on the undersides of leaves, but in heavy infestations they can be found on both sides of the leaves. As they begin to colonize, their webbing becomes obvious.
Each mite puncture produces a tiny light colored leaf spot “stipple” that appears on both sides of the leaf as a silvery to yellowish pinprick size spot which enlarges. The underside of leaves along veins you will see silvery webbing, eggs (nits), fecal deposits (frass), and the mites themselves. Lower leaves (bottom of plant) are usually infested first.
Symptoms are worst during flowering, when whole plants dry up and become webbed together. Short days induce diapause (dormancy) in mites causing them to migrate and cluster together at the tips of leaves and flowering tops. Clusters may become very large.
More than one type of mite may infest a crop at the same time.
This mite overwinters as an adult and emerges in the spring. Females lay over 200 eggs (one at a time) on the undersides of leaves. Eggs hatch into larvae, which molt three times before they are capable of reproduction. There is a 3:1 ratio females to males. Life cycle repeats every eight days. When the days get shorter (autumn to winter), females stop feeding, stop reproducing, turn orange-red, migrate into clusters, and then hibernate under ground litter. Outside when the days get cooler, and food dwindles they too will hibernate. Mites do not like water (humidity).
Adults are plum red to brick red, with dark internal markings. In cooler climates, adults turn green and are even harder to see. In cool climates this pest is limited to glass/greenhouses. High humidity causes all stages (larvae, nymphs, adults) to stop feeding and go into semi-dormancy.
Spider mites can be carried into growrooms on plants, people and pets; they can even float on air currents. Once mites have infested a growroom or glasshouse, you will never get rid of them without removing everything from the space and disinfecting with steam (when water becomes vapor) heat (212 degrees Fahrenheit, 100 degrees Celcius, or 373 degrees Kelvin) or pesticides, yuk!
Hemp Russet Mite (Aculops cannabicola)
The pest thrives in glasshouses and thrives on all kinds of cannabis. Feeds primarily on petioles and leaflets. Mites also infest flowering tops; selectively feeding on pistils, making female flowers sterile. Indoors, mites remain on plants year ‘round. Mites move toward tops of dying plants, where they spread to other plants by air movement (wind) or splashing water. Lifecycle takes about thirty days. No webbing. Pale beige coloring.
Oriental Mite (Eutetranychus orientalis), Privet Mites (Brevipalpus obovatus and Brevipalpus regulosus), and the Ta Ma Mite (Typhlodromus cannabis). These other mites can be confused with spider mites.
Damage is always greatest with drought stressed plants.
Aphids or “plant lice” are tiny, soft-bodied, pear shaped. Longer legs and antennae. Some have bumps on the head between the antennae. Protrusions from the rear help to i.d. them. A pair of tubelike cornicles (siphons) project backwards. The rear end tapers to a pointed, tail-like caudum.
Most adult aphids do not have wings, but some do. The wings are much longer than the body.
Aphids suck sap from a plant’s vascular system, using long narrow stylets. Most aphids are phloem feeders, but some also suck on xylem. Besides sucking sap, they also vector fungi, bacteria, and especially viruses. Viruses and aphids have a symbiotic relationship.
At least six aphid species attack Cannabis. Aphid damage increases in warm, moist weather, with gentle rain and little wind. Damage decreases in hot, dry weather and in the presence of strong, dry winds.
Aphids congregate on undersides of leaflets and cause yellowing and wilting. Some species prefer older, lower leaves, and some prefer younger, upper leaves. Some species infest flowering tops. Early damage is hard to detect. Undersides of leaflets develop light-colored spots, especially near veins. Eventually leaves and flowers look puckered and distorted. Heavy infestation may cause a plant to wilt and die. Surviving plants will be stunted.
Honeydew exudes from the anus of feeding aphids. It may be seen falling as a mist from plants. Honeydew causes secondary problems—ants eat it, and sooty mold grows on it. Ants become bodyguards and attack aphid predators. Sooty mold reduces photosynthesis and leaf transpiration.
Most outdoor aphids migrate between two hosts. The overwintering host is the primary host. Eggs laid on tree limbs hatch into stem mothers or fundatrices. They are born fertile and within days begin giving birth viviparously (eggs hatch inside their reproductive tract)—to “born live” larvae. (discovered by Leeuwenhoek). Fundatrices bear sixty to one hundred fundatrigeniae. Soon these begin giving birth to more live, pregnant, females. In late spring the winged aphids develop and fly off to the secondary hosts, like Cannabis.
Aphids are weak fliers. They fly straight up into a moving air mass. They terminate migration by flying straight down and landing on plants. Once settled on Cannabis, the alatae (winged aphids) undergo four molts in about ten days to reach sexual maturity. Each aptera (wingless) gives birth to thirty to seventy young. Crowding makes these new alatae fly off to new plants. At the end of summer, special alatae (sexuparae) or autumn/return migrants, fly back to the primary host and give birth to ten sexuales. They mate and the females become oviparae and lay five to ten eggs, which overwinter.
A single springtime fundatrix can give rise to up to twelve generations of aphids in one year—600,000 million offspring. In warm glass/greenhouses, aphids do not migrate between hosts, nor do they overwinter eggs. They reproduce parthenogenically all year long, and stay on their secondary host (cannabis).
The Green Peach Aphid (Myzus persicae) attacks many plant species and is very restless; landing on plant after plant, possibly vectoring viruses. This species of aphid is extremely resistant to broad range pesticides.
The Black Bean Aphid (Aphis fabae) is olive green to dull black in color. It migrates between two hosts: Euonymus and Viburnum as primary hosts then to Cannabis as secondary host. This aphid vectors over thirty viruses and is found everywhere except Australia.
The Bhang Aphid or Hemp Louse (Phorodon cannabis) are nearly colorless and twenty five percent smaller than the Green Peach Aphid. It never alternates hosts. It is very damaging to female buds. It sits between female flowers and seeds, sucking plant sap. They vector hemp streak virus, hemp mosaic virus, hemp leaf chlorosis virus, cucumber mosaic, hemp mottle virus, and alfalfa mosaic virus.
Hops Aphid (Phorodon humuli) in California, spring migration peaks June first. The autumn migration peaks in late September. This species vectors many plant viruses and a fungus causing downy mildew. In California, this aphid is aided by a large black ant (Formica subsericea)
Mainly a problem in glass/greenhouses. Look like tiny moths. They are related to aphids and leafhoppers. They damage plants by sucking sap and vectoring plant viruses. Three species infest Cannabis.
Whitefly symptoms—plants lose vigor, leaves droop, turn yellow, wilt, and sometimes die. Leaves are covered with sticky honeydew, followed by a sooty colored fungus.
Adults congregate on undersides of leaves. If you look closely, the adults look like a tiny speck of ash. If you shake a plant, a cloud of whiteflies will fill the air for several seconds.
Eggs are pale yellow with a short stalk that anchors it to a leaf. Eggs turn purple-grey to brown-black before hatching into .3 mm “crawlers.” These first-instar larvae are almost transparent, and have a halo of short waxy threads coming from their bodies. Subsequent instars lose their legs and resemble immature scale insects. Late in the fourth stage, larvae change from transparent to an off-white color. Adult whiteflies rarely measure over 1 mm in length. Their four wings are off-white, rounded, and held flat over their abdomens.
Greenhouse Whiteflies reproduce year ‘round. Females lay one hundred or more eggs on the undersides of leaves near the tops of plants, often clustered in a circle, anchored by short stalks inserted into leaf stomates. Eggs hatch after seven to ten days. First instar larvae crawl around plants searching for feeding sites. Once feeding begins, larvae settle in a spot and start to suck sap, and pupate. Larvae take two to four weeks to reach adulthood, depending on temperature. Adults live four to six weeks. In glass/greenhouses, generations overlap, so all stages occur together. The reproductive rate depends on temperature and host plant. This pest is worldwide and attacks a wide range of crops. It also vectors many plant viruses, including hemp streak virus.
Eggs are oval, white with short stalks anchoring them to leaves. Eggs turn yellow to amber as they mature. Larvae are nearly colorless. Pupae have reddish eyespots, and their bodies are pale. Adults are light beige to yellow with angled wing tips held close to the body. This pest attacks many crops around the world. Can be indoor or outdoor. Indoors they reproduce year ‘round.
Silverleaf whiteflies have devastated growers in the southern USA, indoors and outdoors. More recently have arrived in California. They feed on anything the Imperial Valley has to offer, and are resistant to almost all pesticides. It is very similar to B. tabaci, except the female lays ten percent more eggs. Same temperature, conditions, and host plants. The two species cannot mate.
Whiteflies are attracted to the color yellow. Outdoors, do not plant Cannabis near eggplant, sweetpotato, tobacco or cotton crops. These plants are whitefly magnets. They are slow moving when they are cold (early morning).
ECBs have ravenous appetites and have been recorded feeding on two hundred and thirty different host plants. Native to eastern Europe, they have migrated across most of the USA and Canada. Introduced into California from a cargo of European hemp (1918). Today, only Florida, northern Canada, and sections of the western USA have yet to be invaded.
Young larvae (caterpillars) eat leaves until half grown (through the third instar). They then bore into small branches. Their bore holes extrude a slimy mix of sawdust and frass. Bore holes predispose plants to fungal infection. Within one or two weeks of boring into small branches, ECBs tunnel into main branches and stalks. Their tunnels may cut xylem and cause wilting. Stalks at tunnel sites may swell into galls, which are structurally weak, causing stalks to snap.
ECB larvae born in late summer or autumn will change tactics—instead of boring into stems, they infest flowering tops, wherein they spin webs and scatter feces. They selectively feed on female flowers and immature seeds. Losses can be as high as forty percent.
Eggs are less than 1 mm. long. Just before hatching, the brown heads of larvae become visible within the creamy white eggs. Caterpillars are light brown with dark brown heads. Brown spot-like plates run along the length of their bodies, each sprouting a hair-like body. Mature caterpillars may grow 15-25 mm. long. They spin flimsy cocoons and transform into reddish-brown torpedo shaped pupae (10-20 mm. long). Female moths are beige to dusky yellow, with irregular olive-brown bands running in wavy lines across their 25 mm. wingspan. Males are smaller and darker. Eggs laid on undersides of leaves, stems, or crop rubble. Laid in groups of 15-50. Translucent eggs overlap like fish scales.
Mature larvae overwinter in crop rubble near the soil line. Springtime feeding begins when temperatures exceed fifteen degrees fahrenheit. Larvae pupate for two weeks and then emerge as moths in late May (or June or even August in Canada). Females are strong flyers, seeking host plants to lay eggs. Lay up to 500 eggs in twenty five days. Eggs deposited on lower leaves of the most mature hosts. Artemisia vulgaris is a common host weed. Eggs (first generation) hatch in less than one week.
Larvae feed for about three weeks, then spin cocoons and pupate. Moths emerge, mate, and repeat the life cycle. A hard freeze late in the year kills all but the most mature larvae (those in their fifth instar). One to four generations arise each year. Summers with high humidity and little wind favor egg-laying, egg survival, and larval survival.
Ninety one percent of ECB galls are located in the lower part of Cannabis plants. Avoid planting cannabis near corn fields. Cover glass/greenhouse vents with screens and no lights at night.
Hemp borers also called hemp leaf rollers and hemp seed eaters. Besides boring into stems, they destroy flowering tops, and devour seeds. Each larvae can consume sixteen cannabis seeds. Hemp borers arrived in North America around 1943.
Species are differentiated by their genitalia. Eggs are white to pale yellow and oval (.4 mm. wide) laid singly on stems and leaf undersides. Larvae are pinkish to pale brown (9010 mm. long). Larvae pupate in silken cocoons covered with bits of hemp leaf. Adults are tiny moths, with greyish to rusty brown bodies and brown, fringed wings.
They overwinter as last instar larvae in crop rubble, weeds, or stored seeds. Pupate in April, in soil under plant debris. Moths emerge in early May and migrate at night to new cannabis fields (hosts). They are not strong flyers. After finding new cannabis hosts, females land quickly, mate, females lay 350-500 eggs. Adults live less than two weeks.
Eggs hatch in five to six days (72 degrees to 77 degrees F.), or three to four days (78 degrees to 82 degrees F.). Larvae skeletonize leaves for several days before boring into stems. Borers pupate within stems. Two to four generations overlap.
Larvae go into hibernation in September and October (day length under 14 hours induces diapause). Temperature also influences diapause.
Hemp Borers damage is often in the top third of plants. Late season hem borers can be confused with late season budworms. Breeding short cannabis may decrease hemp borer infestation. Researchers have never found larvae attacking plants less than 30 cm. tall, even when flowering.
Budworms specialize in destroying plant parts high in nitrogen, flowers, fruits, and seeds. Some species skeletonize leaves. Budworms spin loose webs around flowering tops and feed and poo (frass) therein. Wounded buds and frass provide a starting point for grey mold infection.
Eggs are hemispherical, shiny, with ridges that radiate from apex (like spoke wheels), white when new but darkening to tan with reddish-brown ring (.5 mm. in diameter). Newly hatched budworms are pale yellow with dark longitudinal stripes. They grow into stout caterpillars up to (45 mm. long). Mature caterpillars vary in color from green to brown almost black, with alternating light and datrk longitudinal stripes, pale undersides, with yellow-green heads and black legs. Tiny spines cover most of their body. Pupae are shiny brown and found 5 cm. below soil surface. Moths are stout bodied and brown; wings are yellow-brown with irregular lines and dark brown markings near the margins, wingspan up to 40 mm.
Very destructive. One hundred budworms can eat a pound of Cannabis per day.
Produce one to six generations per year depending on the latitude. Tropical populations do not hibernate. Moths can emerge from pupae as late as June and female moths (nocturnal) lay over 1000 eggs, one at a time, on upper leaves of crops and weeds. Eggs hatch in three to five days. Larvae eat leaves, flowers, or seeds. The larval period lasts 14-51 days, depending on latitude. Budworms are cannibalistic.
Very wide host range. Species very similar. Can only tell them apart by genitalia.
lifecycle of cutworms (armyworms)
Cutworms are hemps enemy. Ten species attack Cannabis.
Most farmers are familiar with cutworm damage, but few witness them in action. Cutworms emerge from soil at night to feed on stems and seedlings. The next morning, dead plants are found lying on the ground, severed at the soil line. Older plants may not be completely severed—instead, they tilt, wilt, and die. Cutworms only eat a little from each plant, then move to a new plant. They burrow back into the ground shortly before dawn, usually within twenty five centimeters of damaged plants. Raking the soil to five centimeters will uncover them (rolled into a spiral).
Larvae hatching later in the season (no seedlings to cut), will climb up plants to feed on leaves and flowers. Some species gather in large numbers and crawl “en masse” across fields, eating everything in their path. Earning them their new name armyworms. Armyworms are also called “climbing cutworms.”
There are dozens of leaf-eating caterpillars on Cannabis.
Leaf-eating caterpillars act as leaf rollers (weaving leaves together for protection while they feed), as leaf skeletonizers. Eating leaf tissue between leaf veins, or simply chewing a big hole in leaves. Shaking a plant (early morning), will dislodge leaf-eating caterpillars. Only seven leaf-eating caterpillars are considered serious pests.
Silver Y-Moth or Gamma Moth (Autographa gamma)
Dot Moth (Melanchra persicariae)
Cabbage Moth (Mamestra brassicae)
Garden Tiger Moth (Arctia caja)
Common Hairy Caterpillar (Spiloosoma obliqua)
Beet Webworm (Loxostege sticticalis)
Hemp Dagger Moth (Plataplecta consanguis)
Chrysanthemum Web Worm (Cnephasia interjectana)
Death’s Head Moth (Acherontia atropos)
Thrips are tiny, slender insects. Adults have wings but are poor flyers. The prefer jumping. At least five genera of thrips attack Cannabis. They are mainly a problem in glass/greenhouses and grow rooms that use rockwool and hydroponics. In the old greenhouses with soil floor, watering with a hose kept the floors damp, which encouraged the fungus Entomophthora thripidum. This fungus infects thrips when they drop to the ground to pupate. Now with no damp soil, there is no fungus, and no natural biocontrol.
Immature and adult thrips puncture or rasp surfaces, then suck up exuded sap. This makes white specks or streaks (sometimes silver or yellow) that appear on the undersides of leaves. Infested plants become covered with tiny black specks of thrips feces. Leaves may curl up. Plants wither, brown, and die.
Adults vary in color from pale yellow to dark brown, are pointed at both ends, grow to( 1.2 mm in length). Female’s wings are slender and fringed with delicate hairs. Eggs are white and kidney shaped, oviposited in stems or leaves, and almost invisible to the naked eye. Larvae are small, pale, wingless versions of adults, barely visible without a hand lens. This species pupates in the soil; pupae look like larvae with wing buds.
Outdoor thrips overwinter in soil and plant debris. Glass/greenhouse thrips do not hibernate. Most thrips get active when temperatures reach sixty degrees F. and above. Thereafter, the warmer the temperatures the worse the damage. Females without ovipositors usually lay eggs in cracks and crevices. Those with ovipositors insert their eggs into leaf and stem tissues (protected from biocontrols). Eggs hatch in three to ten days (favorable conditions). First and second instars feed voraciously, become full grown in less than a month. Third and fourth instars (called pre-pupae and pupae) become inactive, do not feed, and go underground. During pupation, thrips get wings (in some species males do not have wings). Males are rare and reproduction is usually parthenogenic (reproduction without fertilization). Both mated and unmated females produce eggs; virgin females generally produce only females. In the field, four generations arise per year, and indoors, up to eight generations.
Onion thrips attack a wide variety of crops. They are very active especially when disturbed. Outdoors, it transmits hemp streak virus and Argentine sunflower virus.
Greenhouse thrips are tropical and found in warm glasshouses everywhere. They attack almost all plants grown in greenhouses. Each female lays forty five eggs. The life cycle turns in as little as thirty to thirty three days. The rectal fluid secreted by larvae protects them from predatores. A sluggish variety.
Adults are yellow. Females ( 1.6 mm in length), males are smaller. Larvae are smaller, lighter in color and wingless.
This species is host specific on Cannabis. Infests leaves and female flowers. Potential vector of plant pathogens. Little known about it.
Indian Bean Thrip (Caliothrips indicus)
Oval, white eggs oviposited in uppersurface of leaves near main veins. Larvae small, pale, and wingless version of adults; feed along veins. Adults are blackish, brown with brown and white banded forewings. Females 1.2 mm in length and males are smaller and lighter brown. Very active. Completes its life cycle in eleven to fourteen days.
Western Flower Thrip (Frankliniella occidentalis)
Kidney- shaped eggs oviposited in leaves near main veins. Larvae cigar shaped, white to pale yellow, red-eyed, and slow moving. Feed along leaflet veins. Female adults vary in color from pale yellow to dark brown, with darker bands across the abdomen, light colored heads, and dark eyes. Hairs on forewings. Females reach 1.3 to 1.7 mm in length. Males are shorter and all yellow.
Infests over two hundred and fifty species of plants and vectors many viruses. They prefer flowers and buds. At optimal temperatures the life cycle turns in seven to thirteen days. Adult females live another thirty to forty five days and lay 150-300 eggs. Mated females produce many more offspring than unmated ones. Species pupates in flowers or in soil (1.5-2.0 cm. deep).
Immature thrips nymphs are impossible to tell apart. Thrips damage looks a lot like other sap-sucking insects, especially spidermites. Mites cause tiny, round lesions on the upper leaf surface, whereas thrips leave irregular shaped lesions on undersides of leaves, lesions often fill the spaces between leaf veins. Thrips nymphs can be confused with leafhopper nymphs.
The most common beetle on cannabis are flea beetles. They damage plants as adults and larvae (grub). Hind legs are large and they leap like fleas when disturbed. Damage consists of many small, round to irregular holes, formed between leaf veins. Leaves may be completely skeletonized. Young plants are killed. Grubs feed on roots at depths of four to eight centimeters underground. They feed on cambium.
Hemp Flea Beetle (Psylliodes attenuata)
Eggs are pale yellow, deposited singly around plant roots near the soil line. Grubs are cylindrical, white with tiny spots and bristles, with six tiny legs, brownish head, 4.5 mm long. Pupae are pearly white that slowly darkens, beginning with the eyes. Adults are oval, black with very tiny grey hairs, 1.3-2.6 mm long. Wing covers are striated. “X” at the eyes, and antennae half their body length.
Adults overwinter in soil, emerge at the end of March to feed on young seedlings. Adults mate in April and begin laying eggs ten days later. Females lay 2.6 eggs per day for a total of fifty five eggs. Egg laying lasts from April to July. Larvae hatch in five to sixteen days, and grubs feed on roots when young. By July grubs exit roots and live in the soil. Pupation is from mid June to August (4-15 cm. underground). Adults emerge from pupae from late June to September. Adults feed on plant tops until autumn, then burrow into soil (to 20 cm.). Only one generation arises per year.
Adults cause more damage than grubs. Two peaks to damage—seedlings when adults emerge in early spring, and again in late summer when adults emerge from pupae. Crop damage increases in warm, dry weather. Adults are most active on warm sunny days.
Leaf damage from flea beetles can be confused with damage caused by leaf-eating caterpillars, weevils, and other beetles. No other beetles leap like fleas.
Leaf eating Beetle mating
Other Leaf Beetles
Other beetles eat holes in Cannabis.
Of all underground insects, white grubs are the most destructive. The grubs often attract moles which become a secondary problem.
Seedlings grow (30-60 cm tall) before they wilt, yellow and die. Damage is patchy in fields. Activity by moles, sod-digging skunks, and raccoons indicates grubs are in the soil.
Grubs hibernate in soil deep beneath the frost line (to 1.5 m. underground). In spring, they return from the deep to feed on shallow roots, spend the summer close to the surface, then return to their deep winter cells. Grubs may run this cycle a third year, depending on the species. Eventually they pupate. Adults emerge from the soil in spring, and feed at night on foliage. At dawn they return to the soil where females lay pearly white eggs in batches of twelve to thirty, under sod or weedy patches of grass. Eggs hatch in three weeks and young grubs feed on roots for the summer.
weevil grubs weevils
Weevils are beetles with long curved snouts. Curculios are weevils with even longer snouts. These snouts sprout antennae and chewing mouth parts. Ten members of this family (Curculionidae) attack Cannabis, the cabbage curculio causes the most damage.
Adults chew small holes in leaves or notch leaf margins. The holes often become surrounded by chlorotic halos. Most larvae (grubs) feed on pith within stems, which causes a swelling in that area. Some grubs feed on roots.
Cabbage Curculio (Ceutorhynchus rapae)
Young larvae are cylindrical, white bodies and brown heads. Older larvae darker in color, plump, and reach 4-6 mm. in length. C-shape when exposed. Adults oval to oblong, grey to black, and covered with yellow to grey hairlike scales. The curved snout is slightly longer than the head and thorax; snout is slender, cylindrical, and antennae arise near its middle. Wing covers have longitudinal ridges. Length 3.5-5.0 mm. When disturbed, they draw in legs and antennae and drop to the ground and play dead (like most weevils).
Adults overwinter and emerge in April-May to mate. Females insert eggs into cannabis stems (young plants). Eggs are always in the lower portion of the stem. Grubs leave exit holes in June to pupate in small coccoons just beneath the soil surface. Adults emerge in June-July and feed on leaves. One generation per year.
This pest was introduced into North America about 1855.
Hemp Weevil (Rhinoncus pericarpius)
Larvae are white with dark brown-black heads; plump, reach 4-6 mm in length. Adults fat ovals, dark reddish-brown to black, sparcely covered with grey-yellow hairs, length 3.5-4 mm. Eggs oval, white.
Live throughout temperate North America, Europe, Asia. Grubs feed within stems causing galls. Galls are weak and may snap. Grubs pupate in stems. Adult beetles feed on leaves and overwinter in the soil. One generation per year.
Adult weevils and curculios may be confused with other beetles until you spot their snouts. Grubs are harder to separate from other stem/root inhabiting beetles (especially grubs of flea beetles). Stem gall symptoms must be differentiated from those caused by caterpillars and gall midges.
Grubs of all these species bore into Cannabis stems and roots.
Tumbling Flower Beetles (Mordellistena)
Longhorn Beetles (Cerambycidae)
Hemp Longhorn Beetle (Thyestes gebleri)
Marsh Beetle (Scirtes japonicus)
green stinkbug (triangle shape on back)
People call a variety of animals “bugs”. True bugs are only found in the insect order Hemiptera. They are distinguished by their wings, which are half membranous, and half thickened and leathery. Many bugs move from host to host. Pest populations build up in weeds and wild plants before they disperse to cultivated hosts.
About a dozen Hemipterans are regularly found on Cannabis, some are serious pests.
True bugs have piercing-sucking mouthparts and feed on plant sap. They feed on the succulent plant parts—unripe seeds, flowering tops, leaves, and young branches and stems. Bud feeders cause late maturity and reduced yields. Some bugs inject toxic saliva as they feed, turning plant tissue into lumpy, brown dead tissue. Adults have a triangle on their backs.
Adults make a stink when handled. Females lay barrel-shaped, pale yellow eggs in batches of 50-60 on undersides of leaves. Nymphs are oval, bluish-green with red markings. Adults are easy to recognize by their flattened shield-like shapes.
Adults are flat and oval, ( 4-7 mm in length), mostly greenish-brown with mottling in reddish, distinct yellow triangle or “v” located on back, yellow wingtips. Nymphs (young) look like yellow-green aphids. More active than aphids. Final instar nymphs have green bodies marked by four black spots on the thorax, one dot on the abdomen, long antennae, and red-brown legs with stripes. Eggs are elongate and curved.
Adults overwinter in soil, weeds, and crop debris. Females emerge in spring andinsert eggs into stems of cannabis and weeds. Nymphs molt five times, gradually taking on the adult appearance. Life cycle takes only three or four weeks, three to five generations each year.
Adults are small (3-4 mm long), grey bodies and lighter colored wings. Nymphs are tiny reddish-brown versions of adults, darkening as they get older.
Adults fly south for winter. Migrate north in spring. Females lay (200-300) eggs on grasses. Adults feed on a wide variety of crops.
Adults elongate, greenish-yellow color, thinly covered with yellow and black hairs, (6-7 mm long),
Overwinters as an egg in stem tissue of plants. This species originated near the Mediterranean, but now lives in North America.
Leafminers tunnel through tissue within leaves. This way they avoid THC and other insecticidal chemicals on the leaf surface. Most are maggots. Can be serious problem in glass/greenhouses. Most tunnels are made on the upper sides of leaves. Tunnels increase in size as the maggots grow in size. Frass is expelled in strips (pellets), or in a big dump at the end of the mine. Heavy infestation leads to reduced crop yield. Mines also provide entrances for fungi and other pathogens.
They overwinter outdoors as pupae. Adults emerge in spring to mate. In warm temperatures (greenhouse), they do not hibernate, but breed continuously. Females drill eggs into leaves one at a time but often clustered. Flies feed on sap oozing from ovipositor wounds. Eggs (up to 350) hatch in two to six days. Maggots of most species undergo four molts, then pupate. Pupation takes one week to several months depending on species and season. Outdoors, two to six generations arise per year; in greenhouses, generations overlap so all stages can be found at any time.
leafhopper leafhopper on cannabis leaf
Leafhoppers, planthoppers, treehoppers, spittlebugs, and cicadas are grouped in a Homopteran suborder, the Auchenorrhyncha. Few cause serious damage, but they can spread plant viruses. They rarely cause economic damage.
Leafhoppers and their relatives are sap suckers. Most are phloem feeders, but some suck xylem sap (cicadas, spittlebugs, planthoppers, and some leafhoppers). Xylem sap is an extremely dilute food source so these pests must ingest great quantities of sap. Spittlebug nymphs can suck xylem sap at a rate greater than ten times their body weight per hour. They digest what they can get out of it, then excrete ninety nine percent of the fluid. They surround themselves with a froth of excreted spittle. Yuk!
Leafhoppers and their relatives cause symptoms similar to those caused by aphids and whiteflies—wilting, stippling of leaves, and sooty mold from honeydew. Xylem feeders also cause leaf veins to become swollen and lumpy, because their stylets are thick and stout compared to the fine flexible stylets of phloem feeders.
Adults small (3-4 mm long), pale yellow-green, iridescent wings extending past their bodies. Two small dark spots between eyes, behind eyes are two larger dark spots, legs and antennae are long. When disturbed (adults) hover over plants like whiteflies. Nymphs are small, white, and almost transparent; wing pads appear during the third instar and enlarge during the fourth (final) instars. Cast off skins from molts remain attached to leaves. Eggs are elongated, white, curved (.5-.7 mm long).
Adults (8-10 mm in length), slender, yellow pointed heads; wings reflect alternate bands of magenta and green with yellow margins. Nymphs are yellow to green
Adults overwinter in leaf trash on the ground. Eggs are thrust into soft plant tissues in early spring. One or two generations arise per year. Infests many hosts, injury rarely serious.
Adults are green with white spots on head and thorax, to (4 mm long). Seen from above, wedge shaped. Nymphs are similar in shape but even smaller and impossible to see as they feed on the undersides of leaves. Nymphs and adults have strong hind legs and jump or “crab walk” when disturbed.
Range is eastern half of North America, cannot overwinter north of the Gulf states. Each spring, adults hitch a ride on air currents (winds) and migrate north. Numbers decrease in low rainfall areas (Western states).
Upon landing, females las thirty five eggs in petioles and leaf veins. Up to four generations arise each year. They feed from both phloem and xylem tissues and often plug these tissues causing “hopperburn” (browning of leaf margins and leaf tips). Affected leaves become deformed, lumpy and curly. Attack over one hundred species of plants.
spittlebug (froghopper) froth from spittlebug
Nymphs easy to spot—occupy crotches of branches and surrounded in froth. Nymphs resemble tiny green frogs (6 mm long). Adult spittlebugs are the same size and shape as final instar nymphs, but turn a mottled brown color and no longer hide in spittle. Eggs ovoid (1 mm long), yellow to white, laid in groups of two to thirty in hardened spittle, on stems and leaves near the ground.
Eggs overwinter. Nymphs feed on xylem sap in spring, and change into adults from late May to late June. Females lay eggs in August-September, then die. One generation per year. Decrease crop yields. Attacks 400 species of plants. Likes high humidity across North America.
Adults green (6 mm long), blunt heads support two short horns. Seen from above, triangular. Adults shy and buzzzzz away. Nymphs are tiny, pale green, humpbacked and covered by spines. Eggs yellow.
Nymphs hatch in spring from overwintered eggs laid in tree branches. They drop to the ground and suck sap from plants. Nymphs feed on cannabis. Damage is done by egg laying females—not feeding, but slicing stems with their knifelike ovipositors to lay eggs. They perforate rings around branches, causing branches to break off. One generation per year.
This species lives throughout North America and causes economic damage in orchards and tree nurseries. They infest marijuana near Buffalo, New York and southern Indiana.
Minor pest of marijuana.
Some cicadas have life cycles as long as seventeen years. Cicadas are recognized by their large size and the males’ summer mating songs. Most of their damage is inflicted on trees.
Mealybugs and scales suck plant sap. They also gum up plant surfaces with honeydew. Honeydew attracts ants and supports the growth of sooty mold.
ant & termite termite
Ants and white ants (termites) curse cannabis in semitropical climates. Though they look somewhat similar, they are from unrelated orders.
Ants and termites tunnel into taproots and stems. Plants wilt and often collapse. Ants also colonize aphid infested plants. Ants protect aphids from predators, and aphids supply ants with honeydew. Leafcutter ants cut pieces of leaves and carry them off to underground nests. Leafcutter ants can devour entire marijuana plants, leaving only roots. Leafcutter ants are nocturnal and can destroy several plants a night.
The red fire ant chews seedlings, tunnels into roots of mature marijuana plants. Workers are (3-6 mm long), and can inflict painful bites and stings.
The species builds mounds (up to 3 m tall). They hollow out the main stem and branches, then the plant collapses.
Damage from ants and termites is similar to damage caused by white root grubs, nematodes, root rots, and assorted fungi and drought.
Gall Midges & Root Maggots
grasshopper on cannabis leaf cricket nymph
The order Orthoptera includes grasshoppers, locusts, crickets, and cockroaches. Somewhat large, elongated insects have prominent eyes, jaws, and large hind legs. They may be winged or wingless. Some in this family are good insects (Praying mantids).
Grasshoppers, locusts and crickets eat large, round, smooth edged holes in leaves. Heavy infestations can strip a plant to the bare stalk in days. Crickets feed on young seedlings, causing cutworm-like damage. Mole crickets feed on roots.
Larvae of crane flies and fungus gnats infest plant roots close to the soil surface. Infested plants lose vigor and color. Scars on roots and fine root hairs are eaten away. Root wounds serve as portholes for pathogenic fungi, and the pests may transmit soilborne pathogens (Pythium and Fusarium).
Crane fly and fungus gnat larvae attack plants that are stressed by nutrient imbalances or waterlogging. They prefer feeding on decaying vegetation and fungi in damp soil. Fungus gnat larvae also feed on the green algae that covers damp rockwool. The adults do not feed on plants. Crane flies are common outdoors, fungus gnats are found indoors.
Adult crane flies look like gigantic mosquitoes. They do not bite humans. The species was introduced into British Columbia and Washington state around 1955. The maggots (leatherjackets), are pink to greyish-black, with black heads, (35-40 mm long). Adults have grey-brown bodies (up to 25 mm long) and delicate milky white wings.
Fungus gnats come from two fly families. For some reason, plants growing in rockwool and sterile potting media are more susceptible than plants growing in soil.
Larvae are slender maggots with translucent bodies and black heads (4-5 mm long). They pupate in soil. Adults are small (2-4 mm long), delicate, humpbacked flies, long legs and beaded antennae, grey to black in color. Poor fliers. Females lay up to 200 eggs on soil or rockwool in seven to ten days. New generations arise on a monthly basis and overlap in warm climates and warm greenhouses. They go unnoticed until you disturb the plant or the soil around the plant.
sawfly sawfly larvae
Sawflies are not flies, they are wasps. Two have been reported on cannabis. One eats leaves, the other bores holes in stalks.
Hemp Sawfly (Trichiocampus cannabis)
Larvae resemble pale caterpillars with dark heads, three pairs of real legs and six to eight pairs of hookless prolegs, grow to (10 mm in length). Adult wasps are (5.5-6.8 mm long) with wingspans averaging (16 mm). Eggs are white, oblong, up to (1 mm long).
Overwinters as mature larvae in soil. Pupation takes five to seven days. Adults live a week in the spring, long enough to lay eggs. Eggs hatch (4-7 days). Larvae undergo five molts before maturity, which takes (27-32) days. Two generations arise per year. Selectively feed on cannabis. Larvae skeletonize leaves or rip holes or tear up leaf edges.
Wireworms are the grubs of click beetles. Grubs feed on roots and freshly sown seeds. They attack many plants especially those in poorly drained soils.
click beetle larvae click beetle adult
Lined Click Beetle (Agriotes lineatus)
Adults light brown with lined wing covers, cylindrical, to (7.5-11 mm long). Grubs are hard, jointed, yellow brown, covered in very small hairs, three pairs of legs behind the head, up to (25 mm long).
Lives its life cycle underground, taking about four years. They can be confused with millipedes.
Small, simple, and very abundant insects. Feed on decaying plant material, fungi, and bacteria.
They damage plants in greenhouses. One species causes stippling of leaves (like spidermites).
Beetle-like appearance, these insects are distinguished by a pair of prominent forcep-like cerci at their tail end. Omnivorous. Nocturnal. They get into everything.
European Earwig (Forficula auricularia)
Adults are dark reddish-brown, (10-15 mm long), pinchers at their bottom end. Female lay round, pearly white eggs underground in masses. Nymphs are pale brown, and their wings and pinchers are much smaller or absent.
Earwigs overwinter as adults in small underground nests. Eggs are laid in late winter and females carefully guard their eggs until they hatch in May. They infest all ages and stages of cannabis, including seedlings and seeds in California.
Hemp Diseases and Pests ( Management and Biological Control), J. M. McPartland, R. C. Clarke, and D. P. Watson. Pgs. 25-92. 2002.