Pests On Hemp: Russet Mites


June 23, 2022
Category: Hemp

Today we’ll discuss how to identify, prevent, and treat hemp russet mites in your commercial greenhouse or industrial hemp field.

What Are Hemp Russet Mites

Hemp russet mites, also known as Aculops cannabicola, are two-legged microscopic mites that are clear or pale in color with oval or elongated bodies. Unlike the two-spotted spider mite, russet mites don’t produce webbing. These pests usually stay on their host plant, but they can spread from leaf edges if plants are touching, and the wind can blow them to new plants.

The hemp russet mite has a 7-30 day life cycle outdoors, depending on environmental conditions in the field. In the greenhouse, this pest population can survive year-round as long as there is a steady supply of new hemp plants to infest.

Whitney Cranshaw, Colorado State University, Bugwood.org

 

Identification and Risk Factors

Since low populations of russet mites often don’t cause visible damage, identifying russet mites on your hemp plants can be challenging. This pest is so minuscule that a hand lens doesn’t provide sufficient magnification to identify it, and you’ll need to check your plants under a microscope. 

Even though these mites are virtually harmless in tiny populations, with enough host plants, a rapidly growing population causes significant damage and resists suppression. 

Look for leaf curling or tiny yellow dots on plant leaves, indicating that russet mites may be sapping nutrients out of leaves. Damage can also include stunted growth and suppressed bud growth as mites grow in the stems and petioles of hemp. Untreated, hemp russet mites can cause irreversible damage and loss in quality and yield in large hemp populations. 

This particular variety of mite has only been observed on hemp and does not seem to flourish in any other crop. Since hemp is a relatively new crop across the country, hemp russet mites also require further study. 

Prevention

The best way to treat russet mite infestations is to prevent them from happening. There are a few ways to go about this. First, you could plant hemp from seed, which is the most effective prevention tactic because hemp russet mites can’t live on hemp seeds. However, the hemp seed industry struggles to produce quality female hemp seeds, so most growers purchase hemp clones. 

When you buy hemp clones, avoid introducing hemp russet mites into your field or greenhouse by washing your plants. Dip each hemp clone in a solution of water and insecticide before bringing it into the field or greenhouse. We dip our plants in insecticidal soap, but any horticultural oil will work.  

Treatment

If you need to treat an active infestation of hemp russet mites, there are a few strategies to try. 

Insecticidal soap, neem oil, or other horticultural oil smothers pests when the spray fully covers each plant. Inadequate coverage will not eliminate mites. Since multiple life stages happen at any given time, spray more than once. 

Alternatively, many hemp growers have switched to using sulfur for powdery mildew and mites on their hemp. You can use sulfur burners, though they are hard on greenhouse plastic. Micronized sulfur, which is sulfur in powder form, will not destroy greenhouse plastic. Sulfur seems to work very well against mites on hemp, which is why many growers have switched to it. However, sulfur has a 24-hour restricted entry interval (REI), so plan accordingly. 

Only insecticides will control a high population of russet mites. However, beneficial mites can suppress small russet mite populations if you don’t want to use insecticides or sulfur. Amblyseius swirskiiAmblyseius andersoni, and Neoseiulus californicus should help control russet mites, though no specific beneficial mites exist to control hemp russet mites. These beneficial mites are generalists. Choose between Andersoni and Swirskii, as they are essentially the same mite bred by different companies. 

For more information about hemp russet mites and how to protect the cannabis crops in your commercial greenhouse or industrial hemp field, look here and here. We would love to hear from you with any questions about growing industrial hemp, employing effective integrated pest management, and succeeding in your commercial greenhouse business.