Problem Identifier / How to Get Rid of Russet Mites

What are Russet Mites?

Russet Mite Under A Miscrocope
Russet mite under magnification. Image source: John M. McPartland & Karl W. Hillig (2003) The Hemp Russet Mite, Journal of Industrial Hemp, 8:2, 109, DOI: 10.1300/J237v08n02_10

A russet mite is an extremely small insect that often attacks cannabis plants. These pests are unable to be seen with the naked human eye. Unfortunately, russet mites are usually not detected until your plants have suffered severe damage. Russet mites are often referred to as hemp mites, with a close relation to tomato mites. They are a member of the Eriophyidae family.

Russet mites on cannabis begin by consuming the leaves close to the base of the plant. The insects will continue eating until the very top of the plant is reached and consumed. When the plants are in the flowering stage, russet mites will consume the flowers. Their movements are generally not noticed until a large population has developed and that is because the damage, at this point, becomes obvious.

Due to their extremely small size, the russet mite often moves by attaching themselves to clothing, on numerous pest insects including aphids and whiteflies, and in removed debris. Proper sanitation in all infested areas is critical for controlling russet mites, as well as implementing an IPM strategy for prevention. The infestation will grow faster when the environment is windless, dry and warm. Plant growth offering both humidity and shelter are a target for russet mites.

Identifying Russet Mites on Cannabis

The size of a russet mite is around 0.2 mm. The mites are thinner and smaller than a single strand of human hair. Since they are microscopic, cannabis growers are usually not aware there is an issue with their crops until it is too late.

Russet mites have a pale coloration, usually yellow or tan. If the numbers are high enough, certain areas of the cannabis plant take on a yellow or beige coloration. In some cases, the insects are mistaken for pollen, mold or fungus. During the winter months, the females remain in the stems of the plants, where the main plant is attached to the branches, or in the root structure.

Hemp Russet Mites
Hemp russet mites developing on new leaves around bud. PHOTO CREDIT Whitney Cranshaw, Colorado State University, Bugwood.org

Russet mites suck the sap from the plants. The feeding starts on the lower plant, moving higher once the food supply is gone. The insects prefer flower resin and are generally undetected when consuming the flower structures. The only way to check for russet mites is by purchasing a magnifier with a minimum magnification of 60x. The higher the magnification the better.

Look for any area where the plant is stressed, use magnification on the area right above. If there are no obvious signs of stress, examine the lower sections of the plant using magnification. If nothing is found, look in several different areas. This is important because once the russet mite has fed, it will move to a different area on the cannabis plant.

Russet mites on cannabis will cause stress and damage. Unfortunately, the only way to stop the pests from killing the plants is to first identify, then get rid of russet mites. A thorough inspection is required to be certain there is no infestation. Growers must know the classic signs of an infestation to understand what to look for. The best option is to examine the plants on a regular basis.

There are handheld digital microscopes available enabling growers to see the underside of the leaves. This makes it possible to take videos and photographs to make a positive identification, determine the size of the infestation, and take the appropriate steps to eliminate the russet mites.

Russet Mite Life Cycle

Currently, there are no thorough studies of the russet mite. Due to the legalization of cannabis in many states, additional research is currently being conducted. What is known of the life cycle is a lot like the other eriophyoids. The entire life cycle can be completed in just 7 to 10 days. This is dependent on the specific environment. Russet mite eggs require two days to hatch.

Once the russet mite eggs have hatched, the larvae appear in roughly three days. In some cases, the larvae will molt into nymphs. The appearance of the nymphs and larvae is a lot like the adult russet mites. Most mites have eight legs, but russet mites only have four in all stages. The females live for a maximum of three weeks and lay between one and two dozen russet mite eggs during their life.

There are no special stages extending the survival of these pests. Russet mite eggs are unable to stay dormant for extended periods of time.

What Does Russet Mite Damage Look Like?

  • Stunted Growth
  • Canoeing of the leaves
  • Misshapen growth
  • Yellow or brown spots resulting from leaf stress
  • Drooping on the top of the plants from a large infestation
  • The edges of the leaves curl on some of the plants
  • Rough, stunted or crinkled leaves
  • Dull coloration on the stems or leaves
  • Brittle leaves
  • Leaves with burned or abnormally curled edges

An infestation can occur in both outdoor and indoor environments. Russet mites are more common in California, Colorado, Oregon and Washington. The visible damage favors the most frequent issues when growing cannabis. The leaves often have a wet and glossy appearance, easily confused with heat stress. The edges of the leaves may canoe with bronze or yellow spotting.

Understanding the symptoms is necessary to get rid of russet mites. Some of the same symptoms are common with mosaic viruses. New growth often appears as limited, stunted or twisted, with drooping leaves. These are the same symptoms as a nutrient deficiency or environmental stress. If the buds become infested during the flowering stage, the plant is generally discarded as worthless.

When cannabis is in the vegetative stage, damage from the mites includes yellowing at the edges of the leaves, extending to the midrib. Once the damage has progressed, the leaves have a necrotic and burned appearance. The leaves may look stunted, crinkled and rough. These patterns are often confused with a virus, fertilizer burn or nutrient deficiency.

When the russet mite starts consuming the flower buds, the pistils of the plant become darker, then prematurely die. The color of the pistils during the start of the flowering stage should be light, vibrant and long. A classic sign of an infestation is smaller buds and browning. Detecting damage on the leaves while the plants are flowering is more difficult than during the vegetative stage.

Look for smaller and rougher leaves, with wilted or slightly burned edges. Often, the edges will be abnormally curled.

How to Get Rid of or Kill Russet Mites Naturally

Russet Mites Under Leaf
Small numbers of hemp russet mites on the underside of a hemp leaf. PHOTO CREDIT Whitney Cranshaw, Colorado State University, Bugwood.org

Russet mite infestations on cannabis can be controlled by applying the following methods:

Micronized sulfur is one of the most effective ways to treat russet mite infestations. Once micronized sulfur is diluted in water, it is mostly commonly applied using a sprayer. Three applications in one week are recommended. Inspect plants and repeat as needed.

When using sulfur, it is important to remember that if oil-based products are applied they can encapsulate the sulfur thus causing a sulfur burn. It is always recommended to rinse your plants with water to remove residual sulfur and to wait a minimum of 72 hours after sulfur is applied before spraying any oil-based products.

Trifecta Crop Control is effective in treating russet mite infestations if the proper application guidelines are followed. Protocol is 2oz of Super Concentrate per gallon of water applied every 48 hours for 2 weeks. Then cut down to every 72 hours for a week. Then down to once weekly at preventative using the following guidelines:

Another natural option is predatory mites such as andersoni or Amblysieus mites. These predators will target the russet mite. Predatory mites can be used for both indoor and outdoor plants. The most commonly used predators include Amblyseius swirskii, Amblyseius andersoni and Amblyseius Californicus. These predators have been proven to be efficient by commercial cannabis growers.

The Stratiolaelaps scimitus (formerly Hypoaspis miles) is a mite dwelling in the soil feeding on pupating thrips, fungus gnat larvae, the root aphid’s larvae stages and pathogenic nematodes. The predators help establish a barrier at the surface of the soil. This often prevents the pests from reaching high enough on the stalks of the plant to reach the leaves. Pest mites can be highly effective for cannabis plants grown indoors.

This is because both the humidity and temperature can be manipulated to help ensure the survival of the predator mites. Although an excellent deterrent, these mites are often not enough to correct the issue by themselves.

Despite the value of cannabis plants, if the infestation is severe enough, the plants may need to be thrown away. New plants should not be grown until the area has received thorough treatment. Determining where the mites originated is critical to ensure the new plants do not become infested.

How to Prevent Russet Mites Naturally

Preventing the mites from attacking the plants is always the best option. This can be accomplished by:

  • Using Trifecta Crop Control as part of a preventative maintenance strategy
  • Growing plants from seeds
  • Quarantine new plants
  • Re-use soil with straw and mulch for predator mite habitats
  • Plant insectary crops and cover crops
  • Do not overfertilize

The essential oils used in Crop Control are an excellent deterrent for all kinds of pests. We always encourage growers to be proactive versus reactive. You will thank us later! Applying Crop Control as part of your IPM will guarantee you never end up with this invisible enemy infesting your plants. Apply as follows:

  • .5oz per gallon applied once per week during veg
  • 1oz per gallon applied once per week during flower up to 2 weeks before harvest

Since russet mites are unable to survive on seeds, plants will remain free of these insects when growing unless an infection occurs from a different source. When introducing new plants, they should be quarantined to make certain no mites are present even if they appear to be healthy.

Soil should be re-used for greenhouses and indoor plants. Adding straw and mulch offers a good habitat for predators. Natural cycles should be used for building the soil. The habitat can be enhanced for a wide variety of soil organisms such as predator mites. The result is vigorous plants free of any pests. If plants are grown outdoors, a beneficial population of arthropods and insects can still be established.

This environment is created by mulching and planting insectary crops and cover crops. Cannabis plants should never be overfertilized. When an excess of nitrogen is present, the vigorous green growth will attract russet mites.

Defeat Pests, Mold and Mildew… NATURALLY!

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