Short answer. Aphids are soft, pear-shaped sap feeders with two tail pipes (cornicles), found in clusters on leaf undersides, stems and later in buds, with white cast skins and sticky honeydew below them. On cannabis the three that matter are the cannabis aphid (Phorodon cannabis), the green peach aphid (Myzus persicae) and the cotton/melon aphid (Aphis gossypii). Every adult is a female that gives live birth without mating, and at 25 °C (77 °F) colonies double every 1.3-2.8 days in lab life tables [7][8][10]. Identify the species, release the matching parasitoid early, and keep sprays out of flower.
Aphid numbers at a glance
| Parameter | Cannabis aphid (P. cannabis) | Green peach aphid (M. persicae) | Cotton/melon aphid (A. gossypii) |
|---|---|---|---|
| Host range | Cannabis only [2][18] | Hundreds of hosts, 40+ families [23] | Very broad (cotton, cucurbits, many ornamentals) |
| Lab host for data | Hemp cv. Henola [7] | Pepper [8] | Cucumber [10]; cotton [11][12] |
| Birth to first reproduction, 25 °C | 6.4 days [7] | 8.3 days (pre-adult) [8] | about 5 days [12] |
| Lower developmental threshold | No published value found (GenetixBay estimate 10-13 °C, see below) | 3.9 °C [8]; 6.5 °C [9] | 6.0 °C [10]; 6.2 °C [11]; 6.3 °C [12] |
| Degree-days, birth to adult | No published value found | 174 DD [8] | 92.6 DD [10]; 108.9 DD [11] |
| Optimum for population growth | 25 °C [7] | 25 °C [8]; 26.7 °C [9] | 22.5-30 °C [10]; 28.6 °C [12] |
| Upper limit | r_m near zero at 30 °C [7] | Upper threshold 37.3 °C; lethal 38.5 °C [9] | Constant 35 °C lethal to nymphs [10][11] |
| Lifetime fecundity | 111.6 nymphs/female at 25 °C [7] | R0 32.5 at 25 °C; 61.6 at 22 °C [8] | 82.1 nymphs/female at 25 °C [10] |
| Peak daily fecundity | 7.5 nymphs/day at 25 °C [7] | No per-day value extracted | No per-day value extracted |
| Intrinsic rate of increase r_m, 25 °C | 0.355 /day [7] | 0.250 /day [8]; 0.356 /day at optimum [9] | 0.526 /day [10] |
| Doubling time (ln2 / r_m), 25 °C | 1.95 days | 2.77 days [8] | 1.32 days |
| Sex ratio | All female while clonal; males only in autumn/short days [4] | All female while clonal | All female while clonal |
The intrinsic rate of increase r_m is the per-day exponential growth rate of an unchecked population; doubling time is ln 2 divided by r_m. These are constant-temperature lab values on single host plants, not field measurements on cannabis, except the cannabis aphid data, which come from hemp [7].
Which aphids attack cannabis, and how do I tell them apart?
Three aphids cause most above-ground damage on cannabis: the cannabis aphid, the green peach aphid and the cotton/melon aphid. Cranshaw and colleagues name the cannabis aphid one of the two most damaging sap-feeding pests of US hemp, alongside hemp russet mite [4]. Cotton/melon aphid has been recovered from greenhouse hemp in Virginia and is reported abundant in indoor cannabis production in the south-eastern United States [4].
Cannabis aphid (Phorodon cannabis). Pale yellow forms predominate, with light green less common; pale pink and light brown forms appear indoors after the switch to short-day light and outdoors late in the season [18]. It develops only on Cannabis [18]. Full ID, life history and control are in Cannabis aphid.
Green peach aphid (Myzus persicae). A generalist on hundreds of host plants in more than 40 families, and a major virus vector worldwide [17][23]. Winged adults are about 1.8-2.1 mm, with a black head and thorax and a yellowish-green abdomen [23]. It is resistant to many insecticides, including pyrethroids [16][17].
Cotton/melon aphid (Aphis gossypii). A small generalist of greenhouse crops. It tolerates heat best of the three, keeping high growth rates up to 30 °C (86 °F) [10][11].
Others. Bean aphid (Aphis fabae) was found on hemp in one eastern Colorado field [4]. Rusty plum aphid (Hysteroneura setariae) was the only aphid recorded on cultivated cannabis in a 1989 Mississippi survey [4]. Larger species such as potato and foxglove aphid matter mainly because they need different parasitoids [5]. Rice root aphid, the commonest aphid in indoor marijuana production in Colorado, lives mostly on roots [4]; see Root aphids.
Why species ID matters. The parasitoid you buy must match the aphid. A pale green, unstriped cannabis aphid can be mistaken for green peach aphid, leading growers to Aphidius colemani, which one trade article calls less effective on cannabis aphid than A. matricariae (trade press; Contested). Many extension labs identify slide-mounted samples.
How do aphids damage cannabis?
Aphids damage cannabis by sucking phloem sap, which at high, sustained numbers slows growth and causes wilting and yellowing [18]. Their stylets slip between cells to the phloem, so there is no stippling or scarring of the kind left by spider mites or thrips [18].
Honeydew and sooty mould. Aphids excrete surplus sugar as honeydew, which lands as small shiny droplets on leaves below the colony [18]. Sooty mould fungi grow black on honeydew, and ants tend aphids for it and fend off their natural enemies [1].
Buds. Cannabis aphid infests maturing flowers and nearby leaflets late in the season and into harvest in Colorado; large numbers of aphids and their eggs can end up in harvested flower, with abundant honeydew [4]. Yield effects are unknown [4].
Viruses. The cannabis aphid can transmit cucumber mosaic virus and alfalfa mosaic virus to hemp [2]. Colorado State notes that the main viruses described from Cannabis are mechanically transmitted, through wounds and cuttings, and cannot be spread by aphids [18]. See Hop latent viroid and viruses.
How do I recognise aphids on cannabis?
Recognise aphids on cannabis by clusters of soft-bodied insects on leaf undersides, along veins, stems and growing tips, with two cornicles at the rear. Supporting signs:
- White cast skins on leaves below colonies, often mistaken for dandruff, mealybugs or mould [18].
- Small shiny honeydew droplets on leaf tops below colonies; later black sooty mould [1][18].
- Ants walking up stems [1].
- Winged aphids on yellow sticky cards [18].
- Swollen tan, bronze or golden "mummies": aphids killed by parasitoid wasps, a good sign [1][5].
Do not confuse with whiteflies (fly up when disturbed; see Whiteflies), mealybugs (waxy, white, slow), or thrips (slender, fast, silvery scars).
What is the aphid life cycle in numbers?
The aphid life cycle indoors is birth, four nymphal instars and a reproducing adult, with no egg and no pupa. At 25 °C (77 °F) a newborn cannabis aphid starts reproducing after 6.4 days on hemp [7], a green peach aphid becomes adult in 8.3 days on pepper [8], and a cotton aphid matures in about 5 days [12].
Viviparous parthenogenesis. Under long days, the colony is all female, and each female gives birth to live, genetically identical daughters without mating [1][18]. UC IPM gives up to 12 nymphs a day and up to 80 offspring a week per adult in warm weather [1].
Telescoping generations. A newborn aphid already carries developing embryos of her own daughters, so the next generation is under way before the current one is bornbeing reviewed. This is why generation time is so short.
Development and reproduction by temperature
| Temp | Cannabis aphid on hemp: pre-reproductive (d) / fecundity / r_m [7] | Green peach aphid on pepper: pre-adult (d) / R0 / r_m [8] | Cotton aphid: immature development / r_m |
|---|---|---|---|
| 15 °C (59 °F) | No data | No data (18 °C: 12.4 d / 52.3 / 0.189) | 10.8 d, r_m 0.208 on cucumber [10]; 12.0 d, r_m 0.177 on cotton [11] |
| 20 °C (68 °F) | 11.0 / 54.5 / 0.153 | 22 °C: 9.6 / 61.6 / 0.233 | First progeny at 8 d on cotton [12] |
| 25 °C (77 °F) | 6.4 / 111.6 / 0.355 | 8.3 / 32.5 / 0.250 | First progeny at 5 d [12]; r_m 0.526 on cucumber [10] |
| 28 °C (82 °F) | 6.0 / 27.8 / 0.244 | 8.1 / 16.6 / 0.214 | Optimum 28.6 °C on cotton [12] |
| 30 °C (86 °F) | 5.4 / 2.4 / 0.019 | 8.5 / 3.4 / 0.108 | 4.1-4.5 d [10][11]; r_m 0.413 on cotton [11] |
| 32-35 °C | No data | 32 °C: 13.0 / 0.22 / -0.097 | 32.5 °C: r_m 0.132 [10]; 35 °C lethal to nymphs [10][11] |
For the cannabis aphid, "fecundity" is mean nymphs per female; for green peach aphid, R0 is the net reproductive rate (daughters per female, survival included). Conditions: cannabis aphid at 65 ± 5% RH, 16L:8D [7]; green peach aphid at 60 ± 5% RH, 16L:8D [8].
Longevity. Cannabis aphid adults lived 24.6 days in total at 25 °C and 15.1 days at 30 °C, with 15.2 reproductive days at 25 °C [7]. Green peach aphid adults on pepper lived about 21 days at 25 °C and about 31 days at 22 °C (read from the published table [8]).
Nymph survival. For the cannabis aphid, 98% of nymphs reached maturity at 20 °C, 71% at 25 °C, 61% at 28 °C and 43% at 30 °C [7].
Degree-days. Green peach aphid needs 174 degree-days above 3.9 °C from birth to adult on pepper [8]. Cotton aphid needs 92.6 DD above 6.0 °C on cucumber [10] or 108.9 DD above 6.2 °C on cotton [11]. For the cannabis aphid, no published threshold was found; a linear fit of the 20, 25 and 28 °C pre-reproductive times in [7] gives roughly 10 °C and 100 DD (two-point fit 20-25 °C: 13 °C and 77 DD). That is a GenetixBay calculation from three points, not a published value.
What triggers winged aphids, and what are holocyclic and anholocyclic cycles?
Winged aphids are triggered mainly by crowding, poor host-plant nutrition and disturbance by natural enemies or other insects, as reviewed by Müller, Williams and Hardie [15]. Most adults in a colony are wingless; winged forms appear when populations are high or food quality declines [1].
Short days. Large numbers of winged cannabis aphids appear on outdoor hemp in September, and Colorado State suggests shortening day length may raise the proportion of winged forms [18].
Holocyclic. A holocyclic aphid has a sexual generation once a year: males and egg-laying females (oviparae) mate and lay overwintering eggs. Green peach aphid overwinters as eggs on Prunus (peach and relatives) in the northern United States [17]. Cannabis aphid is holocyclic on the crop itself outdoors, with winged males and wingless oviparae from early September [4].
Anholocyclic. An anholocyclic population skips the sexual phase and stays clonal all year. Green peach aphid in the south-eastern United States lays no eggs and reproduces by live birth year-round, with up to 30 generations a year [17]. Under indoor long days all three species stay clonal; the cannabis aphid can sustain asexual reproduction year-round under adequate lighting [4].
Grow-room consequence. The switch to 12/12 is a short-day signal. Cannabis aphid can produce sexual forms and eggs indoors after the flip [18]. Green peach aphid and cotton aphid have no such reported response on cannabis (no published data found).
Why do temperature and humidity matter for aphids?
Temperature controls aphid generation time and growth rate; humidity matters mostly through the natural enemies. Between about 18 and 25 °C, warmer rooms raise r_m for all three species [7][8][10]. Above 25 °C the species split: the cannabis aphid collapses by 30 °C (86 °F), green peach aphid declines from 28 °C, and cotton aphid keeps growing fast to about 30 °C [7][8][11].
Heat tolerance differs. At 30 °C the cannabis aphid's r_m fell to 0.019 per day and fecundity to 2.4 nymphs per female [7]. Cotton aphid on cotton still reached its highest r_m, 0.413 per day, at 30 °C [11]. A hot room that suppresses cannabis aphid can favour cotton aphid.
Fluctuating temperatures. Green peach aphid survived daily excursions above its calculated lethal temperature of 38.5 °C for an hour per day, and a constant-temperature model failed to predict development under fluctuating temperatures (R² 0.01) [9]. Lab optima are guides, not set-points.
Grow-room set-points. Typical veg rooms run 24-28 °C (75-82 °F) at 60-70% RH; flower 22-26 °C (72-79 °F) at 45-55% RH; late flower 40-50% RH. Every one of those temperatures is inside the fast-growth window for all three aphids.
Humidity. No published direct effect of RH on cannabis aphid development was found. Humidity matters for control: entomopathogenic fungi need relatively high humidity to work [18], parasitoids perform best at about 70-85% RH [5], and Aphidoletes at 50-85% RH [5]. See VPD.
Diapause in the predator. Short days do not stop aphids indoors, but they can put the predatory midge Aphidoletes aphidimyza into diapause (see biological control below) [5][14].
How fast can an aphid population grow? A worked example
An unchecked aphid colony grows as N(t) = N0 × e^(r_m × t). Starting from 10 cannabis aphids at 25 °C (r_m 0.355 per day [7]), that is about 120 after one week, 1,440 after two and 17,300 after three. At 20 °C (r_m 0.153) the same 10 aphids reach about 250 after three weeks.
Method. Take N0 = 10, the r_m from the life table, t in days. Example: 10 × e^(0.355 × 21) = 10 × 1,728 ≈ 17,300.
| Species, temperature (r_m /day) | Doubling time | Day 7 | Day 14 | Day 21 | Day 28 |
|---|---|---|---|---|---|
| Cannabis aphid, 20 °C (0.153) [7] | 4.5 d | 29 | 85 | 249 | 725 |
| Cannabis aphid, 25 °C (0.355) [7] | 2.0 d | 120 | 1,440 | 17,285 | 207,437 |
| Cannabis aphid, 28 °C (0.244) [7] | 2.8 d | 55 | 304 | 1,680 | 9,270 |
| Cannabis aphid, 30 °C (0.019) [7] | 36.5 d | 11 | 13 | 15 | 17 |
| Green peach aphid, 22 °C (0.233) [8] | 3.0 d | 51 | 261 | 1,334 | 6,813 |
| Green peach aphid, 25 °C (0.250) [8] | 2.8 d | 58 | 331 | 1,906 | 10,966 |
| Cotton aphid, 25 °C, cucumber (0.526) [10] | 1.3 d | 397 | 15,781 | 626,927 | 24.9 million |
| Cotton aphid, 30 °C, cotton (0.413) [11] | 1.7 d | 180 | 3,244 | 58,430 | 1.05 million |
Read this as an upper bound. These numbers assume no predators, no disease, unlimited food and no winged emigration. Real colonies crowd, grow wings and leave, and plants decline. The point stands: two weeks of not looking at 25 °C is the difference between ten aphids and over a thousand.
Where do aphids hide, how do they spread, and how do they get in?
Aphids get into indoor cannabis mainly on infested plant material: clones, mother plants and transplants. Colorado State notes that once a facility is cleared, the only likely route back for cannabis aphid is introduced Cannabis material carrying live aphids [18].
Hiding places. Leaf undersides along the midrib, growing tips, stems and leaf axils; later inside buds [4][18].
Winged dispersal. Winged aphids are weak fliers and largely carried by air currents faster than about 3 mph (about 1.3 m/s) [18]. Airflow direction steers where they settle in a greenhouse: they collect where air flows towards and avoid strong headwinds [18]. See aerial dispersal.
Outdoors and intake air. Generalist aphids migrate from weeds, vegetables and ornamentals; green peach aphid also from Prunus in spring [17]. Unscreened intakes and open greenhouse vents let winged aphids in.
People and pets. Aphids walk slowly and starve within a few days without a host plant [18]. Clothing can carry them from an infested room or garden to a clean one (Grower practice: clean room first, dirty room last).
Ants. Ants move and guard aphid colonies outdoors and in greenhouses [1].
Quarantine. Keep new plant material isolated for several weeks and inspect for honeydew, cast skins, live aphids and winged aphids on cards before it joins the main room [18].
How do I scout for aphids?
Scout for aphids on cannabis at least twice a week during rapid growth, as UC IPM advises for aphid-prone plants [1]. Turn leaves over and check stems and growing tips, using a 10x lens. Look first for honeydew droplets and cast skins, then trace them upward to the colony [18].
Where to look. Leaf undersides of upper and middle canopy, new growth, stems, and plants near intake air and doors. Flag every infested plant.
Lens power. 10-20x confirms an aphid and spots mummies. Separating cannabis aphid from hop aphid needs a microscope (about 40-60x) to see the head and antennal tubercles [2].
Sticky traps. Yellow sticky cards catch winged aphids and show when they disperse; telling winged aphids from fungus gnats and small parasitoid wasps takes magnification and practice [18]. Hang them near, but not touching, plants [22]. No cannabis-specific card density was found; 1 card per 10-20 m² (about 100-200 ft²), changed weekly, is common greenhouse grower practice.
Action threshold. No action threshold has been researched for aphids on hemp or cannabis [2]. Grower practice indoors: act on the first confirmed colony, because the growth table above leaves no room to wait.
Record keeping. Count aphids and mummies on a fixed set of flagged leaves each visit. Rising mummies and falling live aphids mean biocontrol is working.
How do I control aphids by life stage?
Control aphids indoors by targeting nymphs and adults, which are the only stages present while colonies are clonal. There is no egg or pupa to shelter survivors, so contact tactics work, provided they are repeated before newborn survivors start breeding [1][7].
Nymphs and adults. Squash or wipe early colonies; prune heavily infested leaves into a bag. A strong water spray dislodges aphids in veg (Grower practice). Insecticidal soaps (potassium salts of fatty acids) and horticultural oils kill by smothering and only kill aphids present on the day of spraying; coverage of leaf undersides is essential [1].
Re-application interval. Spray again before nymphs born just after a spray can reproduce. From the life tables, that is about 6 days for cannabis aphid at 25 °C [7], 8 days for green peach aphid at 25 °C [8], and 4-5 days for cotton aphid at 25-30 °C [10][11][12]. At 20 °C cannabis aphid takes 11 days [7]. Practical rule: every 5-7 days, at least three applications, in veg only.
Eggs. Eggs exist only after sexual reproduction, outdoors in autumn or, for cannabis aphid, indoors after short days [4][18]. No published data were found on how contact sprays affect cannabis aphid eggs. Removing plant debris after harvest removes laid eggs [18].
Mummies. Parasitised mummies contain developing wasps. Leave them on the plant.
Pesticide resistance. Green peach aphid has evolved resistance to many insecticide classes, including pyrethroids [16][17]. Clonal reproduction multiplies a resistant genotype into a uniform colony within weeks. Rotate modes of action by IRAC group, never repeat one group across consecutive aphid generations, and lean on soaps, oils and biological control. Registrations on cannabis vary by jurisdiction; many places permit none. Follow the label and local law.
Botanicals and fungi. Azadirachtin (neem-derived) is reported to control aphids on hemp, with efficacy still under study [2]. Entomopathogenic fungi such as Beauveria bassiana and Isaria fumosorosea infect aphids and need relatively high humidity [18]. See entomopathogenic fungi.
How does biological control of aphids work in depth?
Biological control of aphids on cannabis works best when the parasitoid or predator matches the aphid species and is released early, at the first colony or before it. Aphidius colemani for green peach and cotton aphid is the standard first choice [5][6].
Parasitoid and predator matching
| Aphid | First-choice parasitoid | Other enemies | Notes |
|---|---|---|---|
| Green peach aphid | Aphidius colemani [5] | A. matricariae [5]; Aphidoletes; lacewings | A. colemani egg-to-adult 9.8 d at 25 °C on this host [13] |
| Cotton/melon aphid | Aphidius colemani [5] | Aphidoletes; lacewings; lady beetles | A. colemani egg-to-adult 10.0 d at 25 °C on this host [13] |
| Cannabis aphid | No proven commercial parasitoid; industry reports favour A. matricariae, with mixed reports on A. colemani [22] | Lady beetles, lacewings, syrphids, Aphidoletes (field) [4] | See Cannabis aphid |
| Potato aphid, foxglove aphid | Aphidius ervi, Aphelinus abdominalis [5] | Aphidoletes | A. colemani is not effective on these [5][6] |
Aphidius colemani
Aphidius colemani is a 2-3 mm braconid wasp that lays an egg inside an aphid; the larva kills it, and the aphid becomes a bronze mummy [20]. Egg to adult takes about 10 days at 25 °C [13], with a lower developmental threshold near 2.7-3.0 °C [13]. Parasitism peaked at 25 °C and declined at 30 °C [13]; extension notes it is less effective above 30 °C (86 °F) [5].
Climate window. Active from 15 °C; optimum 18-25 °C (64-77 °F) at 60-80% RH (biocontrol supplier technical sheet [20]). UConn gives 18-25 °C (65-77 °F) and 70-85% RH for aphid parasitoids generally [5].
Release rates. Biocontrol supplier technical sheets give 0.15-0.25 wasps/m² per release every 1-2 weeks preventively, and 0.5-2 wasps/m² weekly for at least three releases after aphids are found [20]. Mummies should appear 10-14 days after the first release, and control is typically achieved once parasitism reaches about 80% [20].
Banker plants. Wheat or barley carrying bird cherry-oat aphid (Rhopalosiphum padi), a cereal aphid, keeps A. colemani breeding before cannabis is attacked [6]. Suppliers suggest 1-10 banker plants per 10,000 ft² (about 930 m²); start them up to 6 weeks before production, transfer aphids to fresh pots every 2 weeks, and replace declining plants [6]. R. padi is too small to support A. ervi, so this system serves A. colemani only [6].
Aphidius ervi and Aphelinus abdominalis
Aphidius ervi is about twice the size of A. colemani and, with the aphelinid Aphelinus abdominalis, targets large aphids such as foxglove and potato aphid [5]. No published cannabis trials were found for either on cannabis pests.
Aphidoletes aphidimyza, the predatory midge
Aphidoletes aphidimyza larvae eat more than 60 aphid species, with an optimum of 16-27 °C (60-80 °F) and 50-85% RH [5]. Larvae drop to moist substrate to pupate [5]. It was observed feeding on cannabis aphid in Colorado hemp fields [4]. One supplier's cannabis program lists 1 midge/m² weekly from first detection [21].
Short-day diapause. UConn states larvae need at least 15.5 hours of light to avoid diapause, with no second generation in short days [5]. In a Chinese strain, diapause occurred mainly at 15-20 °C under 8-14 h of light, reached 88.7% at 15 °C, and was 0% at 25 and 30 °C under every photoperiod [14]. A Japanese strain had a critical day length of 12.7 h at 20 °C [14].
Cannabis consequence. Under 12/12, expect the midge to work as a single release generation unless the room runs at 25 °C or more (strain-dependent; Contested). Night-break lighting, the greenhouse trick for keeping Aphidoletes active, interrupts the long night that cannabis needs to flower. Do not use it in a flowering room. See Light leaks.
Lacewings and lady beetles
Green lacewing larvae (Chrysoperla, Chrysopa spp.) reduce aphids in about 2 weeks and leave greenhouses above 35 °C (95 °F) [5]. Lady beetle larvae may eat 500-1,000 aphids each [5]. Field-collected convergent lady beetles (Hippodamia convergens) often arrive semi-dormant and may take a few weeks to lay eggs [18].
Predator:prey ratios. No published predator:prey or parasitoid:aphid release ratio for cannabis was found. Use supplier per-m² rates and the 80% parasitism target as the working benchmark [20].
Spray compatibility. Soaps and oils kill exposed adult wasps and predator larvae on contact but leave little residue [1]. Spray, let it dry, then release (Grower practice). Check residue history before releases [20].
How can the room environment be used against aphids?
The room environment slows aphids only modestly, because every common indoor set-point is inside their growth window. The useful levers are favouring the parasitoids, steering winged aphids with airflow, and starving the colony of soft growth and ants.
Temperature. At 20 °C (68 °F) cannabis aphid r_m is 0.153 per day versus 0.355 at 25 °C [7]: doubling time stretches from 2 to 4.5 days. Running mother rooms and clone areas at 20-22 °C buys time for scouting.
Do not run hot to fight aphids. Cannabis aphid collapses at 30 °C in the lab [7], but cotton aphid is near its optimum there [11], A. colemani loses effectiveness above 30 °C [5], and the plant suffers. See Heat and light stress.
Humidity for beneficials. Parasitoids prefer 60-85% RH [5][20]. That fits veg (60-70% RH) and mother rooms. In flower, 45-55% RH is a compromise against botrytis and powdery mildew; do not raise flower humidity to help beneficials.
Airflow. Winged aphids ride air currents above about 3 mph (1.3 m/s) [18]. Positive pressure and filtered intakes keep them out; strong headwinds keep them off clean zones.
Nitrogen. Soft, high-N growth is a better aphid host (Grower practice; USU advises avoiding excess nitrogen [3]). Poor host quality triggers winged forms [15], so a declining plant sends aphids to its neighbours.
What should I not do about aphids in flower?
In flower, do not spray soaps, oils or botanicals onto buds. Residues stay on harvested flower, and wet buds invite bud rot. Rely on beneficials released before or at the flip, removal of infested branches, and early harvest of badly infested plants.
No systemics. Systemic insecticides are not registered on cannabis in most places and persist into flower. Follow the label and local law.
No night-break lights. Lighting to keep Aphidoletes out of diapause breaks the 12-hour night and risks reverting or hermaphrodite flowers.
No humidity raises. Raising RH for fungi or parasitoids in late flower trades an aphid problem for a bud-rot problem.
Cut out honeydew-coated buds. Honeydew and sooty mould in buds lower quality and feed mould [4]. Bag and remove those sections.
Watch for eggs after the flip. Cannabis aphid can produce sexual forms and eggs under short days [18]. Clean all debris after harvest [18].
What are the common myths about aphids on cannabis?
The common aphid myths concern lady beetles, wasp choice, eggs, heat and viruses. Evidence labels follow the GenetixBay ladder.
- "Garden-centre ladybugs will clean up indoor aphids." Myth for indoor rooms. Field-collected convergent lady beetles arrive semi-dormant and may take weeks to lay eggs; larvae do most of the eating [5][18].
- "Any Aphidius kills any aphid." Myth. A. colemani is not effective on large foxglove and potato aphids [5][6]; cannabis aphid lacks a proven commercial match [4][19].
- "Aphids lay eggs that hatch after you spray." Myth indoors under long days: the colonies are clonal and viviparous [1][18]. Eggs appear only with sexual forms [4][18].
- "Run the room hot to kill aphids." Contested. Cannabis aphid collapses at 30 °C [7], but cotton aphid thrives there [11] and the plant and parasitoids suffer [5].
- "Aphids spread hop latent viroid." Myth. The main Cannabis viruses described are mechanically transmitted [18]; cannabis aphid carries cucumber mosaic and alfalfa mosaic virus [2].
Common mistakes
- Buying a parasitoid before identifying the aphid.
- Waiting for "a few more" aphids: at 25 °C a colony doubles in 2-3 days.
- Ignoring ants, which guard aphids from beneficials [1].
- Spraying soap once and stopping; one spray only kills what it touches [1].
- Releasing Aphidoletes into a cool 12/12 room and expecting a second generation [5][14].
- Bringing in clones without quarantine [18].
- Using broad-spectrum sprays that kill established parasitoids and cause a rebound.
Evidence
- Viviparous parthenogenesis, honeydew, winged dispersal: Established [1][15][18].
- Cannabis aphid life table on hemp: Supported, one lab study at four constant temperatures, 65% RH, 16L:8D [7].
- Green peach and cotton aphid life tables: Established across several studies; values vary with host plant and clone [8][9][10][11][12].
- Aphidius colemani for green peach and cotton aphid: Established in greenhouse crops [5][13]; cannabis-specific trials sparse.
- Biocontrol of cannabis aphid by specific parasitoids: Grower practice and trade reports [22]; peer-reviewed data minimal [4][19].
- Aphidoletes short-day diapause: Established; thresholds strain-dependent [5][14].
- Action thresholds on cannabis: none researched [2].
