Hemp russet mites (HRM) are microscopic pests that can lead to major problems. HRM are an emerging pest of concern in Cannabis and there is currently little known about its biology. Presented below is what we do know.
Biology of HRM
The hemp russet mite (HRM) is a member of the Eriophyidae family.
They are very tiny, visible only with magnification. HRM have a cigar shaped body and are pale in color with 4 limbs. They prefer to inhabit the underside of leaves near the petiole and typically are not noticed until population levels are high, and plant damage becomes visible.
Their life cycle is not well understood, but consists of an egg, nymph, and adult stage. The length of their life cycle is likely dependent on environmental conditions, but like many eriophyid mites it probably takes approximately seven days to complete.
The nymph and adult stages of HRM cause damage to growing plants by piercing and sucking cell contents, damaging plant cells. When HRM populations get high (lol, no pun intended but appreciated) damage may appear as upward or downward curled leaves, a bronzing of the leaves or stems, and brittle foliage.
IPM control of HRM
How can you best control HRM? Don’t let it in your facility. That is not very helpful, but it is the best measure so far. Thoroughly inspecting new plants or clones is critical to preventing HRM. Once an infestation happens, quarantining infected plants is essential.
Some pesticide options may be available depending on your state, but consideration into the safety of end use products needs to be taken. Biological controls such as predatory mites may help, but there is currently little information on the effectiveness of these options.
In worst case scenarios, your only option may be to destroy your current crop, clean the space, and let sit plant-free for 14 days. This ensures that any remaining adults or nymphs are starved out.
Again, the best protection against HRM is to prevent them from entering your facility. You can save money, time, and stress later by spending a little more time inspecting at the beginning. Insecticidal soaps, pesticides, and biocontrol may all be viable options, but there is currently little information available on their effectiveness.
I highly recommend visiting your state universities extension service website if you have a problem with hemp russet mite. New information is coming to light everyday which means IPM guidelines for control are likely to be changing as well.
