Short answer. White cottony tufts in branch crotches and along stems, with slow oval insects underneath, are mealybugs, on indoor cannabis usually the citrus mealybug (Planococcus citri). They are slow: about four weeks egg to adult at 25 °C and a population doubling roughly every 8 days [6]. Their wax shrugs off contact sprays, ants protect them, and they hide in places you do not look. Control rests on clean clones, ant control, repeated treatment across the 10-20 day egg-laying window in veg [1], and Cryptolaemus plus Leptomastix in rooms kept above about 20 °C [7][8].
Which mealybugs attack cannabis?
Mealybugs on indoor cannabis are occasional pests, not key pests: Colorado State University's list of key hemp pests does not include them [14], and we found no published cannabis-specific mealybug life table. The species involved are the general greenhouse mealybugs, brought in on plants. Supported (extension consensus for greenhouses; cannabis evidence anecdotal).
| Species | Where on the plant | How to tell it | Reproduction |
|---|---|---|---|
| Citrus mealybug, Planococcus citri | Stems, leaf axils, branch crotches, under leaves, buds | Oval, white wax, short equal-length side filaments, sometimes a darker line down the back [1][2] | 300-600 eggs in a cottony ovisac [2] |
| Longtailed mealybug, Pseudococcus longispinus | Stems and foliage | Two tail filaments as long as or longer than the body; 17 pairs of marginal filaments; female up to about 3 mm (1/8 inch) [1][2] | Live young; no egg masses [1] |
| Root mealybugs, Rhizoecus spp. | Roots, rootball surface | Bluish-grey to bluish-white, elongate-oval, up to 2.35 mm, short antennae, nearly eyeless, white cottony wax between pot and rootball [2][12] | 17-83 young per female in 1-3 litters (R. hibisci) [12] |
| Solenopsis mealybug, Phenacoccus solenopsis | Stems and foliage | Host lists include Cannabis sativa [13] | Mainly outdoor/warm-climate; not well documented indoors |
Mealybugs are true bugs (Hemiptera: Pseudococcidae). Females are wingless and stay mobile through their lives, unlike armoured scales. Males are tiny, winged, short-lived and do not feed [2].
Many species can reproduce without mating [1]. A single female arriving on a clone can start a colony.
How do you recognise mealybug damage on cannabis?
Mealybug damage on cannabis shows as white cottony masses, sticky honeydew, sooty mould and slow, weak growth near colonies. Mealybugs suck phloem sap, and heavy colonies reduce plant growth [1].
- Cottony tufts in leaf axils, branch crotches, on stems and on the undersides of fan leaves. Citrus mealybug ovisacs are the tell [1][2].
- Honeydew makes leaves below colonies shiny and sticky; black sooty mould grows on it [1].
- Ants walking up stems are often the first visible sign [1].
- In flower, colonies inside dense colas are almost impossible to remove; contaminated buds are unsaleable.
- Root mealybugs show no specific top symptom; plants decline slowly. The infestation is not evident until the rootball is removed from the pot [12].
Differentials. Powdery mildew is flat, powdery and has no bodies (see white powder on leaves). Spider mite webbing is fine silk. Whitefly nymphs are flat, scale-like ovals under leaves. On roots, see the next section.
How do you tell root mealybugs from root aphids and perlite?
Root mealybugs (Rhizoecus) are slow, bluish-white oval insects with cottony wax and no tail-pipes; root aphids are olive-green to brown, faster and have cornicles. Under a 10x lens the difference takes seconds.
| Feature | Root mealybug (Rhizoecus) | Rice root aphid | Perlite |
|---|---|---|---|
| Colour | Bluish-grey to bluish-white under wax [2][12] | Dark olive-green to brown | Bright white, glassy |
| Shape and size | Elongate-oval, up to about 2.4 mm [12] | Round, pear-shaped aphid | Angular grains |
| Cornicles (tail-pipes) | None | Present | n/a |
| Wax | White cottony wax on rootball surface, especially against the pot wall [12] | Little wax; white cast skins | n/a |
| Movement | Very slow, slower than springtails [2] | Walks when disturbed | None |
| Development | 2-4 months egg to adult (R. hibisci) [12] | 4-21 days, temperature-dependent | n/a |
See root aphids for the full root comparison, including fungal hyphae.
What are the citrus mealybug life-cycle numbers?
Citrus mealybug life-table data come from lab studies on coffee, coleus, citrus and grapevine; none used cannabis. The figures agree on the big picture: development stalls below about 10 °C, runs fastest at 25-28 °C and fails at 35 °C.
| Parameter | Value | Host, conditions and source |
|---|---|---|
| Female nymphal development (crawler to adult) | 76.6 days at 15 °C; 35.2 at 20 °C; 23.2 at 25 °C; 30.0 at 30 °C | Coffee, lab, 70 % RH [3] |
| Male nymphal development | 37.9 days at 20 °C; 24.1 at 25 °C; 19.8 at 30 °C | Coffee, lab [3] |
| Egg to adult (preadult) | 28.3 days (females), 26.3 (males) at 25 °C | Grapevine, lab, 65-70 % RH [6] |
| Nymphal mortality | 80 % at 15 °C; 45 % at 20 °C; 30 % at 25 °C; 72.5 % at 30 °C; 100 % at 35 °C | Coffee [3] |
| Temperature range for completing development | Females 15-32 °C; males 18-32 °C; no first instars survived at 10, 12 or 37 °C | Coleus, lab [5] |
| Lower developmental threshold | 10.6 °C, female nymphal period, 334.9 degree-days | Coffee [3] |
| Lower developmental threshold | 7.15 °C, egg to adult, 526.3 degree-days | Citrus, lab [4] |
| Optimum and upper threshold | Optimum 27.85 °C; upper 33.64 °C | Citrus, lab [4] |
| Eggs per female | 300-600, in an ovisac | Extension [2]; UC: 100-200 or more for most mealybugs [1] |
| Egg-laying period | 10-20 days | Extension [1] |
| Egg hatch | Within a few days | Extension [2] |
| Adult longevity | 14.8 days (total adult); 34.0 days whole life | Grapevine, 25 °C [6] |
| Peak fecundity | 23 °C | Coleus [5] |
| Net reproductive rate R0 | 32.1 offspring per individual at 25 °C | Grapevine [6] |
| Intrinsic rate of increase r_m | 0.084 per day at 25 °C | Grapevine [6]; on coleus r_m peaked at 25 °C [5] |
| Finite rate of increase λ | 1.087 per day at 25 °C | Grapevine [6] |
| Mean generation time T | 41.4 days at 25 °C | Grapevine [6] |
| Doubling time | 8.3 days (ln 2 / 0.084) at 25 °C | Calculated from [6] |
| Generations per year | 2-6 outdoors; continuous indoors | Extension [1] |
| Sex ratio | No published value found in the abstracts used | — |
Degree-day check. Using 526.3 degree-days above 7.15 °C [4], egg to adult is about 41 days at 20 °C, 29 days at 25 °C and 23 days at 30 °C. The 25 °C figure matches the 28.3 days measured on grapevine [6]. The linear model overestimates speed near the upper limit: on coffee, female nymphs took longer at 30 °C than at 25 °C [3].
Longtailed mealybug and root mealybugs. We found no comparable temperature-dependent life table for Pseudococcus longispinus in the sources used. For Rhizoecus hibisci, egg to adult takes about 2-4 months, adult females live 27-57 days and eggs hatch in under 24 hours [12].
Why do temperature and humidity matter for mealybugs?
Temperature sets how fast citrus mealybugs breed, and normal cannabis rooms sit in their sweet spot. On coleus, fecundity peaked at 23 °C and population growth at 25 °C [5]; the citrus study put the optimum near 27.85 °C [4]. Veg rooms at 24-28 °C and flower rooms at 22-26 °C both suit them.
Heat helps them until about 30 °C. Above 30 °C nymphal mortality climbs (72.5 % at 30 °C on coffee) and at 35 °C all nymphs died [3]. The upper threshold estimate is 33.64 °C [4]. No cannabis room should run that hot for long.
Cool slows them hard. At 15 °C female nymphs took 76.6 days on coffee, with 80 % mortality [3]. Cool nights in a dark period slow development but do not stop it.
Humidity. The lab studies ran at 65-80 % RH [3][5][6]. We found no published study isolating RH effects on citrus mealybug development. Wax protects mealybugs from desiccation, so dry flower rooms (45-55 % RH, late flower 40-50 %) do not stop them (Grower practice).
Humidity matters more for the natural enemies. Cryptolaemus develops and reproduces fastest at 22-25 °C (72-77 °F) and 70-80 % RH [7], and Leptomastix prefers warm, sunny, humid conditions [8]. Late-flower rooms at 40-50 % RH and cooler nights are below the beetle's comfort zone.
No diapause indoors. Under warm indoor conditions all stages are present year-round [1].
How fast can a mealybug population grow? A worked example
Ten citrus mealybugs at 25 °C become about 58 in three weeks and about 1,500 in 60 days, in the unchecked exponential model. The calculation uses N(t) = N0 × e^(r_m × t) with r_m = 0.084 per day at 25 °C on grapevine [6].
| Days | Mealybugs at 25 °C (r_m 0.084/day) |
|---|---|
| 7 | about 18 |
| 14 | about 32 |
| 21 | about 58 |
| 42 | about 340 |
| 60 | about 1,500 |
| 90 | about 19,000 |
Method. N0 = 10; r_m = 0.084 per day [6]; doubling time = ln 2 / 0.084 = 8.3 days. At 60 days: 10 × e^(0.084 × 60) = 10 × e^5.04 ≈ 1,545.
The authors' own projection is lower. Kına and colleagues projected 357 individuals at 60 days from 10 eggs [6]. Their stage-structured projection starts from eggs, which take weeks to start reproducing; the simple exponential assumes the stable age mix from day 1. Both are upper bounds with no natural enemies.
Compare with fast pests. Rice root aphid at 25 °C has an r_m of 0.432 per day (see root aphids), five times higher. Mealybugs are slow, which is why a cannabis crop of 10-14 weeks often finishes before a small infestation becomes a disaster, and why infestations go unnoticed in mother rooms that run for years.
Where do mealybugs hide, how do they spread and how do they get in?
Mealybugs reach indoor cannabis almost always on plants: rooted clones, mothers, houseplants and ornamentals carried into the grow [2]. Adult females cannot fly, so they do not blow in.
- Clones and mothers. Long-lived mothers are the classic reservoir: slow pests build up in plants kept for years (Grower practice).
- Houseplants and ornamentals. Citrus mealybug is common on citrus, indoor ornamentals and greenhouse crops and is usually brought indoors on an infested plant [2].
- Crawlers. First-instar crawlers walk between touching plants and are carried on hands, clothing, tools and air currents (Grower practice).
- Ants. Ants move and guard mealybugs [1].
- Root mealybugs spread via purchased infested plants, crawlers from nearby hosts, reused pots, reused media and irrigation water [12].
Hiding places. Leaf axils, branch crotches, under bark-like lower stems, the base of the stem at the medium surface, inside trellis knots and plant ties, pot rims, under trays and in cracks in benches (Grower practice). Root mealybugs hide between the pot wall and the rootball [12].
How do you scout for mealybugs?
Scout for mealybugs by checking stems, axils and crotches of every incoming plant and of mothers weekly, by watching for ants and honeydew, and by unpotting a sample of plants for root mealybugs. No published action threshold exists for cannabis; any confirmed colony on a mother or in flower warrants action (Grower practice).
- Incoming plants. Inspect every clone and plant for cottony tufts, stems and leaf axils, and unpot to look at roots. Quarantine for at least four weeks, about one egg-to-adult cycle at 25 °C [6]. Grower practice.
- Weekly mother checks. Look into branch crotches and at stem bases with a 10x lens. Grower practice.
- Ants and honeydew. Ant trails or sticky shiny leaves trigger a close search [1].
- Root checks. For root mealybugs, slide plants out and look at the rootball surface against the pot wall [12].
- Sticky cards catch winged male mealybugs only; they do not show females and are a poor monitoring tool for mealybugs (Grower practice).
- White card trick. A white, non-sticky card near infestations attracts Cryptolaemus adults [7], which shows where released beetles are active.
Lens. 10x shows crawlers, filaments and ovisacs; 20x helps confirm young crawlers and parasitoid exit holes in mummies.
How do you control mealybugs by life stage?
Mealybug control by life stage comes down to one fact: eggs in ovisacs and waxed adults are shielded, crawlers are exposed. UC IPM notes that wax makes contact insecticides less effective and younger nymphs are more susceptible [1]; NC State adds that contact products usually need two or more applications to catch nymphs hatching from protected eggs [2].
| Stage | Exposure | What reaches it |
|---|---|---|
| Eggs in ovisac | Protected by cottony wax | Physical removal; Cryptolaemus adults and larvae eat eggs [7] |
| Crawlers (1st instar) | Most exposed, least wax | Contact sprays in veg; predators |
| Older nymphs | Increasingly waxed | Leptomastix (prefers 3rd instar) [8]; older Cryptolaemus larvae [7] |
| Adult females | Heavily waxed, in crevices | Leptomastix (young adults) [8]; Cryptolaemus; hand removal |
| Longtailed mealybug | Live-bearing, no ovisac [1] | Crawlers appear continuously |
Registrations differ by jurisdiction. Follow the label and local law. No products or rates here.
Repeat interval. Each female lays eggs over 10-20 days [1] and eggs hatch within a few days [2]. In veg, a contact program (insecticidal soap, horticultural oil) must repeat every 5-7 days for at least four weeks to keep killing new crawlers until the last protected eggs have hatched and before those crawlers mature (about 23-29 days to adult at 25 °C [3][6]). Calculation from [1][3][6]; Grower practice for interval.
The program is long because the pest is slow. A six-week generation time [6] means you need a six- to ten-week campaign, not a one-off. Stopping after two sprays because the cotton is gone is the common failure.
Resistance. Mealybugs breed slowly, so resistance builds slowly, but parthenogenetic reproduction [1] means survivors pass on their traits intact. Rotate modes of action by class; IRAC group numbers on any registered label identify the class. Systemic classes are the "reliable" option in ornamentals [2] but are unregistered on cannabis in most places.
Spot treatments. UC IPM suggests swabbing individual mealybugs on houseplants with 70 % or weaker isopropyl alcohol [1]. On a few veg plants, it works; on a room, it does not; on flowers, never.
Which biological controls work on mealybugs?
Biological control of citrus mealybug indoors rests on the predatory beetle Cryptolaemus montrouzieri and the parasitoid wasp Leptomastix dactylopii, often released together [8]. Anagyrus parasitoids add coverage. All need warmth, egg masses or the right host stage, and ant control.
Cryptolaemus montrouzieri (mealybug destroyer)
- What it eats. Adults and young larvae mainly eat mealybug eggs and young nymphs; older larvae eat mealybugs of any age. Each larva can eat over 250 nymphs or 1,000 eggs [7].
- Temperature and RH. Fastest development and reproduction at about 22-25 °C (72-77 °F) and 70-80 % RH; below 20 °C (68 °F) and with short day lengths, reproduction slows greatly [7]. One lab study on P. citri found a lower developmental threshold of 11.5 °C, an upper of 25.5 °C and 400 degree-days for the immature stages [9].
- Development. Eggs hatch in about 5 days at 27 °C (80 °F); larvae feed 3-4 weeks; egg to adult takes 4-6 weeks in warm conditions [7].
- Reproduction. Females live about 2 months and lay 200-400 eggs; eating the waxy eggs of egg-sac-producing insects stimulates laying [7]. Release where egg sacs are plentiful.
- Release. UC IPM suggests one or more releases of several beetles per square foot of growing area or per plant where egg masses are present in greenhouses and interiorscapes [7]. Check the sex ratio: healthy shipments are about 50:50; females have black to dark-brown front legs, males orange [7].
- Look-alike warning. Cryptolaemus larvae are covered in long wax filaments and look like large mealybugs. Brush the wax: beetle larvae have visible legs and mouthparts [7]. Do not spray them.
Leptomastix dactylopii (parasitoid wasp)
- Hosts. Best known as a citrus mealybug parasitoid. UC's Pest Note says it kills only citrus mealybug [1]; UC's natural enemies gallery says it attacks at least 50 mealybug species, including longtailed mealybug [8]. UF EDIS notes that females reared on vine mealybug produce fewer, smaller offspring than on citrus mealybug [11]. Use it for P. citri. Contested breadth.
- Stages attacked. Prefers third-instar nymphs and young adult females; one egg per host; the host becomes a mummy [8].
- Development. About 3 weeks egg to adult at warm temperatures [8]; 15-16 days egg to adult on vine mealybug third instars (UF EDIS citing Muştu et al. 2022) [11].
- Fecundity. Each female parasitises about 60-100 mealybugs in her life [8].
- Temperature. Progeny production rose and adult longevity fell as temperature increased from 18 to 30 °C [10]. It prefers warm, sunny, humid environments [8].
Anagyrus spp.
- Anagyrus pseudococci (in the 1989 study) is another encyrtid parasitoid of Planococcus mealybugs; like Leptomastix, its progeny production rose with temperature from 18 to 30 °C [10]. Its temperature-dependent development on vine mealybug has been modelled [15]. Use it alongside Leptomastix where suppliers offer it.
What the natural enemies need
- Ant control first. Ants attack mealybug natural enemies [1][8].
- Warmth. Keep the room above about 20 °C during release periods for Cryptolaemus [7].
- No broad-spectrum, persistent insecticides [7][8]. Soaps and oils kill exposed beetle larvae and wasps on contact; time any spray before releases.
- Reduce dust and offer nectar sources where possible [7][8].
- Expect weeks. With a 4-6 week beetle generation [7] and a 3-week wasp generation [8], suppression takes one to two natural-enemy generations.
Root mealybugs are not reached by Cryptolaemus or Leptomastix. In other crops, hot-water immersion of potted plants (49 °C water until the rootball reaches 46 °C) was 100 % effective on palms [12]; that is unsuitable for cannabis roots. Discard infested plants and media.
How can you use the environment against mealybugs?
Environment is a weak lever against citrus mealybug in cannabis, because its optimum of 25-28 °C [4][5] is a normal cannabis set-point. The real environmental play is making the room good for the natural enemies.
- Keep release rooms at 22-26 °C and 60-70 % RH in veg to suit Cryptolaemus (fastest at 22-25 °C, 70-80 % RH [7]).
- Do not chill rooms to slow mealybugs. Cooling to 15-18 °C slows the pest (76.6 days nymphal at 15 °C [3]) but stops Cryptolaemus reproducing below 20 °C [7] and slows the crop.
- Do not heat rooms to kill them. Development fails at 35 °C [3], which is crop-damaging heat.
- In flower, hold normal humidity (45-55 %, late flower 40-50 %) for botrytis and powdery mildew control, and accept that natural enemies will work more slowly.
What not to do about mealybugs in flower
In flower, contain mealybugs; do not try to spray them out of buds.
- Do not spray soaps, oils or alcohol on flowers. Residues stay on trichomes and wet buds invite botrytis.
- Do not use systemic insecticides. Most are unregistered on cannabis and persist into harvest.
- Do not take clones from an infested plant, and do not keep it as a mother.
- Do: remove and bag heavily infested branches, release Cryptolaemus where egg sacs are present, control ants, isolate plants, and inspect harvested material before drying.
- After harvest: bag plant waste in the room, clean benches, trellis and pots, and restart with inspected clones.
What are the common myths about mealybugs?
- "Mealybugs explode like spider mites." Myth. r_m is about 0.084 per day at 25 °C [6], several times lower than mites or aphids. Their danger is that they go unnoticed.
- "One spray clears them." Myth. Wax and ovisacs shield adults and eggs; repeats are required [1][2].
- "Leptomastix only attacks citrus mealybug." Contested. UC sources disagree [1][8]; it performs best on citrus mealybug [11].
- "Cryptolaemus works in any room." Myth. Reproduction slows greatly below 20 °C [7].
- "Ants are harmless." Myth. Ants guard mealybugs and attack their natural enemies [1][8].
- "Sticky cards will show mealybugs." Grower practice says no. Only winged males are caught.
How do you confirm mealybug control worked?
- Two consecutive weekly checks, at least four weeks after the last live female was seen (one egg-to-adult cycle at 25 °C [6]), find no live crawlers, nymphs, adults or fresh white ovisacs.
- Old ovisacs are empty or contain parasitoid-killed mummies with round exit holes.
- No fresh honeydew and no ant trails.
- Root checks show no bluish-white insects or fresh wax against the pot wall.
Common mistakes
- Treating cotton, not insects: the wax stays after the mealybugs die, and new ovisacs look the same.
- Stopping after two sprays when the egg-laying window is 10-20 days [1].
- Releasing biological control without killing the ant trail first.
- Spraying Cryptolaemus larvae because they look like mealybugs.
- Releasing Cryptolaemus into a cool or late-flower room below 20 °C.
- Keeping an infested mother for years.
- Bringing houseplants or citrus trees into the grow area.
Evidence
- Citrus mealybug development, survival and population growth versus temperature: Established for coffee, coleus, citrus and grapevine in the lab [3][4][5][6]; not measured on cannabis.
- Wax reducing contact-spray efficacy, crawlers as the susceptible stage, ant protection: Established (extension consensus) [1][2].
- Cryptolaemus and Leptomastix biology: Established [7][8][9][10][11]; release efficacy on cannabis: Grower practice.
- Leptomastix host range: Contested [1][8][11].
- Mealybugs as cannabis pests: Supported by host records [13] and grower reports; not a key pest in university hemp lists [14].
- Root mealybug biology: Supported for ornamentals [12].
