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How to identify it
- They are far too small to see with the naked eye, about 110 to 210 micrometers long, or roughly twice the width of a human hair. Seeing them takes a lens of at least 15 to 20x.[1][2][3]
- They are pale white to yellowish, with a wormlike body that is covered in fine crosswise ridges and tapers sharply at the rear. Unlike spider mites, they have only two pairs of legs, set near the head.[1][3]
- They spin no webbing, which helps separate them from many other pest mites.[2][3]
- Because the injury can look like disease or other plant stress, confirm it under a microscope. Leaves can be examined directly, or washed in soapy water or 70% ethanol and the wash viewed against a dark background.[2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Spider mites | Hemp russet mites have only two pairs of legs, unlike spider mites, and they make no webbing. Two predatory mites used against twospotted spider mites, Phytoseiulus persimilis and Amblyseius californicus, do not work against hemp russet mites.[1][2][3] |
Where it lives
Extension entomologists in Kentucky and North Carolina describe it on hemp grown both in greenhouses and in open fields.[1][2]
Biology and life cycle
A generation can be completed in about a week under favorable conditions, especially high heat and humidity, and the mites can live up to 30 days. Eggs hatch into two nymphal stages before the adult stage, and generations overlap.[1][3]
Mites start on the undersides of leaves and, as numbers grow, spread to the upper leaf surface, leaf stalks, stems and flower buds. Populations build up most in the growing tips.[1][3]
They are too small to travel far on their own, but they crawl to leaf edges and are carried off by the wind.[2][3]
Indoors they survive year-round on a steady supply of new plants. Colorado State says they overwinter outdoors in crop debris, while NC State notes it is not known how they survive between field plantings.[2][3]
In greenhouses, heat and high humidity during propagation speed their reproduction, and ventilation can spread dense populations quickly. They are likely carried on cuttings as eggs or active mites.[1]
Damage and signs
- The mites pierce leaf cells and remove the contents. Heavy feeding curls leaf edges up or down, gives leaves and stems a bronzed or rusty look, and leaves foliage smaller, dull or brittle; badly hit plants are dusted with a brown or tan powder of shed skins.[1][2][3]
- Feeding in the growing tips stunts plants and can kill young seedlings and newly rooted clones.[1]
- Damage to flower buds means fewer and smaller buds and lower yield and cannabinoid content. In outdoor Kentucky hemp, populations run highest from August to October, as the flowers develop.[1][2][3]
- Low numbers cause no visible injury, and in North Carolina fields fairly heavy infestations did not always produce obvious damage.[3][2]
Health risk
It feeds only on cannabis and hemp plants. The Kentucky, NC State and Colorado State sources mention no risk to people or pets.[3][1][2]
Control
Prevention
Start with clean plants. Seed is the safest start, since the mites cannot survive on seed. If you use cuttings, inspect both the cuttings and the mother plant and make sure mites are absent or scarce before planting.[2][1][3]
Sanitation
Clean tools after working on infested plants, and limit the movement of people and supplies from infested areas to clean ones. In the field, remove and destroy infested plants.[3][2]
Established infestations are very hard to eliminate where plants are grown continuously. Clearing all plants out of the infested area works, because without host plants the remaining mites die within a month.[3]
Biological control
The predatory mite Amblyseius andersoni feeds on russet mites, though its value against hemp russet mite in field plantings is unclear.[3][2]
Pesticides
Highly refined mineral oils and seed oils such as neem, soybean, cottonseed and canola oil have been used. They kill only the mites they coat and have no residual activity, so coverage must be thorough; in Kentucky trials in 2021, mineral oil-based and biological products worked best.[2][1]
Few products are registered for hemp and the rules keep changing, so check your state's list of pesticides registered for hemp, or ask your county extension agent, before treating.[1][2]
Common questions
- Why are my hemp leaves bronzed and curling when I can't see any bugs?
- Hemp russet mites are one possibility. They are too small to see without strong magnification, and heavy feeding curls leaf edges and gives leaves a bronzed or rusty look; a microscope check confirms them.[1][2][3]
- Do hemp russet mites make webs?
- No. They spin no webbing, which helps tell them from many other pest mites.[2][3]
- Can hemp russet mites come in on clones?
- Yes. They are likely carried on cuttings as eggs or active mites, which is why both the cuttings and the mother plant should be inspected before planting.[1][2][3]
Sources
- University of Kentucky Entomology, “Hemp Russet Mite, a Key Pest of Hemp in Kentucky, ENTFACT-162 (R. Villanueva, Z. Viloria, R. Ochoa and A. Ulsamer, March 2026).” entomology.ca.uky.edu/ef162 (accessed 2026-11-08)
- NC State Extension, “Hemp Russet Mite in Industrial Hemp (M. Pulkoski and H. Burrack, August 2020).” content.ces.ncsu.edu/hemp-russet-mite-in-industrial-hemp (accessed 2026-11-08)
- Colorado State University, Department of Agricultural Biology, “Hemp russet mite (IPM pest page).” agsci.colostate.edu/agbio/ipm-pests/29895-2/ (accessed 2026-11-08)
- iNaturalist, “Aculops taxon page (order and family).” www.inaturalist.org/taxa/142109 (accessed 2026-11-08)