Using Predator Bugs to Control Unwanted Pests in Your Cannabis Garden: Russet Mites

Nathan Jackson

For Oregon Cannabis Connection

The Pest:
Hemp Russet Mite Aculops cannabicola

First signs:

Lack of plant vigor, curled or taco-shaped leaves, yellowing and dropping of leaves. Hemp Russet Mites are the newest plague to hit cannabis growers. These tiny pests pack a punch. They cause

severe damage and can spell disaster to any grow, from small to large. Many gardeners don’t even know they have them until it is too late.

Russet mites are members of the eriophyid family of mites. Unlike spider mites, which have four pairs of legs, russet mites have two pairs of legs. They look like small translucent cylinders that are tapered on one end. Some growers say they look like a miniature Jabba the Hutt, from Star Wars. They do not create webbing and are not visible to the naked eye. You might be able to see them with a 10-power magnifier, but a 60 to 100x is much better. Access to a quality microscope can make detection much easier. They tend to stay on the upper side of the leaf, and prefer the area where the stem meets the leaf.

Female russet mites can overwinter in the plant tissue, often inside the stem. They also lay eggs on the plant or in the soil. After the eggs hatch, they go through two nymph stages, which are very similar in appearance to the adults. They take as little as eight days to mature to adults, and can have multiple overlapping generations.

Russet mites don’t move very far on their own. They can get caught in light breezes that move them from plant to plant, and can even hitch a ride on whiteflies and other small pests. It’s been reported that strong airflow from commercial atomizers can spread them around the garden. They like to stay in one area and suck the sap and juices from plants. They can feed directly from resin glands on flowering plants, and can even survive for a short period of time on dried buds. They inject a poison into the plant that causes leaf disorders for several feet upward in the plant. Some growers like to apply one crushed non-coated aspirin per gallon of water to counteract the effects of the poison. Infected plants often are lacking in vigor and look weak. Leaves can turn yellow and might fold into a taco shape or fall off. The plants might appear to be deficient in calcium and magnesium, but no amount of cal-mag makes any difference.

Control:
What is the best way to deal with russet mites?

As with all insect pests, prevention is important. Rigorously inspect new plants before they enter your garden or grow room. Do not visit somebody’s garden and then go to your own without changing clothes and, ideally, taking a shower. Inspect your own plants regularly. Several beneficial insects eat russet mites.

Predator nematodes have been used to control soil pests for many years. They are an inexpensive control for russet mites emerging from the soil and will help control virtually any pest with a soil stage. For best results use predator nematodes that have been raised on a live insect diet. Apply at a rate of one million per 2,000 sq. ft.

Hypoaspis miles (also known as Stratiolaelaps scimitus) are small mites that lives on the soil surface. They can help control russet mites as they hatch in the soil. Hypoaspis should be applied to the soil at a rate of 5,000 per 200 sq. ft. of soil. They will help with early stages of russet mites, so apply soon after the plants are in soil and reapplied every two to four weeks.

Amblyseius swirskii are very effective predators of russet mites. They should be used as soon as the temperature is above 70 degrees. Cannabis application rates vary, but for large plants use 250 to 1,000 per plant for a bad russet mite outbreak. For prevention on smaller plants reduce the amount used. A. swirskii can also eat certain stages of thrips and whiteflies.

Amblyseius andersoni have been used in the past to control spider mites, but also work great against russet mites. They are slightly more cold-hardy than other predators, so they can be used when daytime temperatures are a little lower (mid 60s.) Application rate for traditional crops is three predators per 10 sq. ft., but for russet mite control on cannabis you may easily increase that by tenfold.

Aw other russet mite predators are worth mentioning. Neoseiulus californicus, Amblyseius fallacis, and Amblyseius cucumeris have been used in IPM (integrated pest management) for decades. They can be used with any of the other russet mite predators to increase the biological diversity among your plants and give you the best chance for a successful grow.

Russet mites can be expected to  be an ongoing pest problem, just like spider mites have been for the last 40 years. Being able to recognize the symptoms and identify the pest itself is important. Take proactive measures and have a good population of beneficial insects on your plants before the first russet mite shows up. Remember, an ounce of prevention is worth a pound of the medicine.

Nathan Jackson is the owner of Nature’s Control and Ladybug Indoor Gardens. Located in Phoenix, Oregon, Nature’s Control has supplied growers with beneficial insects for over 35 years. He can be reached at 541-245-6033 or nathan@naturescontrol.com.