Pests
Identification, life cycles, thresholds and IPM.
Aphids on cannabis: species, life tables, population growth and IPM
Three aphids matter on cannabis: the cannabis-only cannabis aphid (Phorodon cannabis), the green peach aphid (Myzus persicae) and the cotton/melon aphid (Aphis gossypii). All breed without mating and give live birth, with intrinsic rates of increase of about 0.25-0.53 per day at 25 C, so a colony doubles every 1.3-2.8 days. Identify the species, then release the matching parasitoid early; keep sprays out of flower.
Broad mites on cannabis: life table, spread and control (plus russet mite summary)
Broad mites (Polyphagotarsonemus latus) twist, glaze and harden cannabis new growth. At 25 C a generation takes about 4.4 days from egg to adult and populations can double in about 2.2 days (grape-leaf lab data), so control rests on clean stock, quarantine, preventive predatory mites (Amblyseius swirskii, Neoseiulus cucumeris, N. californicus) and repeat treatments timed to the life cycle. Hemp russet mite has its own article.
Budworms on cannabis: corn earworm and tobacco budworm in numbers
The 'budworm' that ruins outdoor cannabis colas in the US is mostly the corn earworm (Helicoverpa zea), with the tobacco budworm (Chloridea virescens) mixed in; both need about 422 Celsius degree-days above 12.6 C to go from egg to adult (about 34 days at 25 C), lay up to ~1,500 eggs per female singly on flowers, and open the door to bud rot, so growers trap moths from late July, scout buds weekly in flower and hit hatchlings with Bt within the first week after egg hatch.
Cannabis aphid (Phorodon cannabis): ID, life table, overwintering and control
The cannabis aphid (Phorodon cannabis) develops only on Cannabis. It was first recognised as a pest in North America on Colorado hemp from 2015. On hemp at 25 C it starts breeding 6.4 days after birth, produces about 112 nymphs per female and doubles every 2 days (r_m 0.355/day), but it nearly stops growing at 30 C. Short days trigger males and egg-laying females outdoors and after the indoor flip. Quarantine clones; no parasitoid has been proven against it in peer-reviewed trials.
Caterpillars on cannabis: species, degree-days and control
Caterpillars on cannabis are mostly an outdoor, late-season problem: corn earworm budworms bore into colas and start bud rot, European corn borer and Eurasian hemp borer tunnel stems and buds, and armyworms and loopers chew leaves. Each species has a degree-day clock (lower thresholds about 10-14 C), so trap the moths, scout for eggs and hatchlings, exclude moths with netting, and use Bt or other biologicals on newly hatched larvae before they bore in.
Fungus gnats: the watering problem with wings
Fungus gnats (Bradysia impatiens, B. coprophila) breed in constantly wet, organic, microbially active media. At about 25 C a generation takes roughly 17-22 days and the population can double about every 6 days (r_m 0.111/day). Larvae chew roots of seedlings and clones and can carry Pythium; adults do not. Dry the top of the medium, then use Bti, Steinernema feltiae, Stratiolaelaps scimitus or Dalotia coriaria, with yellow cards and potato slices to count.
Hemp russet mite (Aculops cannabicola): life cycle, detection and control
Hemp russet mite (Aculops cannabicola) is a 0.11-0.21 mm eriophyid mite that lives only on Cannabis, bronzes and curls leaves upward from the lower canopy and moves into buds. It is invisible below about 15-20x and needs about 55x to count. No life table exists for it; its relative the tomato russet mite completes egg-to-adult in 5.5 days at 25 C with an r_m of 0.286 per day. Clean stock and quarantine are the main defences; most growers treat it as zero tolerance in mothers and clones.
Integrated pest management (IPM) for cannabis: a complete programme for home and small commercial growers
A cannabis IPM programme is a written routine: keep pests out (clean stock, a 14-21 day quarantine, clean-room-first workflow), find them early (weekly leaf and card scouting with set thresholds), act by life stage and temperature (predators first, contact tools only in veg, rotation by mode-of-action group), and record every count so the next run starts smarter.
Leafhoppers on cannabis: beet leafhopper, curly top and hopperburn
Leafhoppers matter on cannabis for one reason above all: the beet leafhopper (Circulifer tenellus) spreads beet curly top virus, which was found in 81% of symptomatic hemp samples in Colorado in 2019 and has no cure. Potato leafhopper causes hopperburn but is usually a minor pest. Protect young outdoor plants with barriers, control weed hosts, monitor with yellow sticky cards and rogue infected plants; insecticides cannot stop a virus transmitted within hours.
Mealybugs and root mealybugs on cannabis: ID, life cycle in numbers and IPM
Mealybugs are occasional, slow-building pests of indoor cannabis, usually the citrus mealybug (Planococcus citri), sometimes the longtailed mealybug or root mealybugs (Rhizoecus). They are slow: about 4 weeks egg to adult at 25 °C and an r_m near 0.084/day (doubling in about 8 days, lab data on grapevine), with development failing at 35 °C. Wax shields them from contact sprays, ants farm them, and control rests on clean clones, ant control, and Cryptolaemus and Leptomastix released above about 20 °C.
Root aphids (rice root aphid) on indoor cannabis: ID, life cycle in numbers and IPM
The 'root aphid' of indoor cannabis in North America is mainly the rice root aphid (Rhopalosiphum rufiabdominale). At 25 °C it doubles in about 1.6 days (r_m 0.432/day, lab data from Tsai and Liu 1998), it reproduces only asexually indoors, and winged alates spread it plant to plant. Control rests on clean clones, removing every root between runs, a plant-free gap, and fungal drenches; nematodes and soil predators are unproven.
Shore flies: algae farmers in your propagation tray
Shore flies (Scatella stagnalis, S. tenuicosta) breed in algae on wet media, rockwool, benches and floors. Larvae eat algae, not roots, but larvae and adults carry Pythium, Thielaviopsis, Fusarium and Verticillium in their gut and frass. At 25 C S. stagnalis goes egg to adult in 11.4 days and multiplies at r_m 0.263/day. Control is algae and puddle management first; Bti and soil mites do little, rove beetles and repeated nematode drenches help.
Slugs and snails: night shift on your seedlings
Slugs and snails, above all the gray field slug Deroceras reticulatum, chew smooth-edged holes in cannabis seedlings and young transplants at night in cool, wet weather. They lay clutches of about 10-40 eggs and do best near 17-20 C. Scout at night or under boards, protect seedlings with iron phosphate baits, copper barriers and traps, and remove hiding places.
Spider mites on cannabis: life tables, ID and IPM
The twospotted spider mite (Tetranychus urticae) causes pale stippling and, at high numbers, webbing on cannabis. In lab life tables its intrinsic rate of increase roughly doubles from about 0.16 per day at 20 °C to about 0.30 per day at 30 °C, so 10 females can become several thousand in three weeks in a warm room. Control rests on early scouting, cooler and less dry veg rooms, predatory mites released early, and contact sprays timed to the egg stage and kept out of flower.
Temperature, humidity and pest population growth in cannabis: every major pest compared
Room temperature is the single biggest lever on how fast cannabis pests multiply: between about 20 and 30 C, most mites, aphids and thrips double every 2-4 days in lab life tables, while mealybugs and fungus gnats double every 6-8 days. Humidity matters mostly through the predators and pathogens that control pests, so set-points should be chosen for the beneficials as much as against the pest.
Thrips on cannabis: life table, temperature, scouting and biological control
Thrips rasp leaf cells and leave silvery scars dotted with black fecal specks. Western flower thrips needs about 268 degree-days above 7.9 °C per generation (about 16 days at 25 °C) and can grow by r = 0.12-0.23 per day. Eggs sit inside leaf tissue and most pupae sit in the medium, so control has two levels: predators that eat larvae on the foliage, and soil predators or nematodes for the pupae, all set up in veg.
Two-spotted vs carmine spider mite: one species or two, and does it matter?
The carmine spider mite (Tetranychus cinnabarinus) is now usually treated as the red form of the twospotted spider mite, Tetranychus urticae, because red and green mites interbreed, overlap in every morphological character and do not separate in DNA studies. Some researchers still use the old name. For a cannabis grower the colour form changes almost nothing: the same predators, the same humidity and temperature logic and the same acaricide rotation apply; resistance depends on a population's spray history, not its colour.
Whiteflies on cannabis: life table, temperature, parasitoids and IPM
Whiteflies are tiny white moth-like sap feeders that rise in a cloud when you shake a plant; nymphs sit flat under leaves and drip honeydew. Greenhouse whitefly needs about 381 degree-days above 8.3 °C per generation (about 23 days at 25 °C) and prefers moderate rooms; silverleaf whitefly grows fastest at 25-27 °C (r about 0.19 per day). Identify the species, monitor with yellow cards, and release Encarsia formosa (greenhouse whitefly, rooms above about 18-20 °C) or Eretmocerus (silverleaf, warm rooms) plus A. swirskii early in veg, keeping sprays out of flower.
