Hemp Russet Mites
Hemp russet mites are tiny bugs that attack cannabis plants. In fact, they are so small you can only see them with a magnifier unless there are thousands of them infesting your plant. They live the the crevices of leaves, stems or buds, and the initial symptoms are not that serious. Many growers may not realize they have a bug infestation, and it’s common for growers to confuse the symptoms for other problems such as mold, fusarium, pollen, tobacco mosaic virus , overwatering , a nutrient deficiency or heat damage .
You may see curling on the edges of leaves, and buds may start dying (hemp russet mite leaf damage picture by thehumboldtlocal)
Hemp russet mites are tiny. You often won’t see them until you have a full infestation. They may appear as a beige or yellow mass (typically towards the tops of the plant). This hemp russet mites picture is by grow.nation.
The following two pictures of Hemp Russet Mites (Aculops cannabicola) were taken in Bloomington, Indiana by Karl Hillig. This picture shows hundreds of microscopic mites on the petiole of a Cannabis leaf.
These microscopic four-legged mites infested Cannabis plants in a greenhouse at Indiana University. This picture shows them on a leaf petiole that was about 2 mm wide. By Karl Hillig.
Symptoms of hemp russet mites on cannabis include:
- Symptoms often worst towards the tops of the plant
- Bugs are pale, typically either tan or yellow. In big enough numbers they can cause parts of the cannabis plant to look beige or yellow.
- Sometimes mistaken for fungus, mold or pollen.
- Tops of plants droop, especially where there is a big infestation
- Curling of the leaf edges (on some plants)
- Dull-colored and leaves or stems, which may also become brittle. These affected areas are where bugs are living inside the plant tissue.
- Brown or yellow spots (from leaf stress, not visible bites)
An intense hemp russet mite infestation on cannabis plants can be difficult to diagnose because it’s hard to see the individual bugs
The yellow mass isn’t mold or pollen. It’s actually an infestation of hemp russet mites
About hemp russet mites
- Can reproduce and attack cannabis plants all year round
- Most harmful in the flowering stage when buds get infested
- Indoors, fans can spread mites
Unfortunately, hemp russet mites are one of the toughest cannabis pests to get rid of. They lay their eggs inside the plant which makes it very difficult to kill their eggs.
- Grow from seeds (hemp mites and eggs cannot survive on seeds). If you start from seeds, your plants will not get hemp russet mites unless they get infected by some other source
- Treat and quarantine all new plants (even if they seem healthy) to ensure they don’t have hemp russet mites (or spider mites)
Time to get rid of hemp russet mites for good.
Solution: How to Get Rid of Hemp Russet Mites On Cannabis
Once you’ve actually identified that the bugs you have on your cannabis are hemp russet mites, it’s time to get rid of them! When it comes to hemp russet mites, a lot of the “standard” miticides are not as effective and you’ll notice these particular mites aren’t listed on the labels.
Hemp russet mites can be one of the toughest marijuana pests to get rid of, but it can be done if you stay vigilant!
- Consider tossing your plants – I know it can be a hard pill to swallow, but if you have an intense infestation, sometimes the easiest thing to do is to get rid of the plants, treat the room thoroughly, and start over. However, make sure you know where you got the mites in the first place or you may end up infected again!
- Treat often – You may have to treat several times a week or even daily if you have a terrible infestation that won’t go away. This can be very difficult on your plants.
- Spray Before Lights Go Out – Whenever treating plants with a spray, do it before the lights go off so that your plant is less likely to get burned!
- Read Instructions – Make sure to read the full instructions of each bottle and follow them when treating your plants. You will save yourself a lot of big headaches!
- Repeat treatments weekly for 5 more weeks after mites are gone – After you think hemp russet mites are completely gone, don’t stop! Treat your plant with a different treatment at least once a week for 5 additional weeks. If you don’t completely eradicate them they’ll come back with a vengeance and be even more resistant to whatever you throw at them.
1.) Neem Oil
Neem Oil will leave an unpleasant taste/smell on buds when used to treat flowering plants, so again, don’t let this stuff get near your buds! There’s also some evidence Neem oil may be harmful to humans so use with care! That being said, Neem oil is an all-natural remedy that is very effective against many different types of bugs and mold, including hemp russet mites.
Neem oil can be rough on your plants so you don’t want to use it more often than you have to because your plants will suffer. However, if you get desparate treating plants daily with Neem oil is very effective at killing hemp russet mites when nothing seems to be working.
You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly, since neem oil and water can separate easily.
2.) Essentria IC3
Essentria IC3 Insecticide is a mix of various horticultural oils that is organic and safe for humans. It is often marketed as a “bed bug killer” but it can be effective against hemp russet mites when the plants are treated regularly. Unfortunately it only stays effective on the plant for about 8 hours so you will want to either apply this daily or combine with other options. You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly.
3.) Insecticidal soaps
Fatty acid salts or insecticidal soaps can be a good choice against hemp russet mites. They weaken the outer shell of hemp russet mites but are safe to use on your plants and they don’t leave much of a residue which could kill beneficial bugs in your garden.
With soaps, just like horticultural oils, coverage is very important as it does not stay on your plant for long, so follow-up applications may be necessary. Although this is considered safe, avoid getting any on your buds!
This will not get rid of hemp russet mites on its own, but it is less harsh on your plants than some of the other options and so it can be a great way to supplement the other treatments you’re doing.
Natria Insecticidal soap can be a good option Another insecticidal soap that can be used against hemp russet mites is Safer Brand Soap
4.) Mighty Wash
Mighty Wash may help rid your grow room of hemp russet mites. Spray plants 15 minutes before lights out, making sure to drench the foliage under the leaves as well as the top of your soil. You want to use a spray bottle or mister. Use a fan to blow on your leaves to help things dry. Treat your room more than once, even if you believe the hemp russet mites are gone.
Use Mighty Wash with a One-Handed Power Sprayer for the best results!
Avid miticide is strong stuff with harsh chemicals, and is incredibly expensive, but it can sometimes do the job when nothing else is working. This is a systemic insecticide, which means it works by infiltrating the inside of plant tissue and killing bugs that way. Because of that it should NOT be using in the flowering stage (you don’t want this stuff inside your buds). However, many growers report that this is the only thing that consistently works for them. Always use Avid as directed and only as a last resort! You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly.
Don’t use this product more than once or twice in a row or your mites may become resistant. This should stay in your plant’s system for several weeks. If you’re going to be using systemic insecticides, switch back and forth between this and another one like Forbid. Make sure to follow the instructions!
Forbid miticide is sort of like Avid in that it is made of strong stuff with harsh chemicals and is also expensive. This is a systemic insecticide, which means it works by infiltrating the inside of plant tissue and killing bugs that way. Because of that it should NOT be using in the flowering stage (you don’t want this stuff inside your buds). However, many growers report that this can be the only thing that consistently works for them. Always use Forbid as directed and only as a last resort! You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly.
Don’t use this product more than once or twice in a row or your mites may become resistant. This should stay in your plant’s system for several weeks. If you’re going to be using systemic insecticides, switch back and forth between this and another one like Avid. Make sure to follow the instructions!
7.) Diatomaceous Earth
Diatomaceous Earth is basically fossil dust which you mix in with the top of your soil, and anywhere else in your room (window sills, doorways, etc). This powder-like substance is harmless to mammals and plants, but is incredibly sharp at the microscopic level. Therefore it will tear and dehydrate hemp russet mites on physical contact. This will not get rid of an infestation, but can help prevent, control and slow things down when used effectively! When it comes to hemp russet mites, you want to use every tool you can!
Hemp russet mites don’t like the heat. Some growers will try to get rid of them by on small plants or clones by dunking the plants in hot water (105°F / 40°C) for 10-20 minutes. I’ve also heard of growers try to reduce their number by overheating the grow space to 115°F (46°F) for an hour. Be careful as this can be dangerous if you don’t take safety precautions, and any heat method strong enough to kill the mites will likely hurt your plants.
9.) Predatory Mites
Some types of predatory mites, like Amblysieus andersoni mites, may target hemp russet mites. Supplementing your garden with extra predators can help bring down hemp russet mite numbers. However, it’s not enough to fix the problem on their own and unfortunately a lot of the other remedies on this page may also kill predatory mites.
If you don’t want to use any pesticides, get predatory mites to help eat all your hemp russet mites!
- Bronze or brown patches
- Brown or slimy roots
- Brown or yellow leaf tips/edges
- Buds dying
- Buds look odd
- Bugs are visible
- Curling or clawing leaves
- Dark leaves
- Drooping plant
- Holes in leaves
- Mold or powder
- Pink or purple on leaves
- Red stems
- Shiny or smooth leaves
- Spots or markings
- Twisted growth
- Wilting leaves
- Yellow between leaf veins
- Yellow leaves
This page is part of our Plant Doctor series. You can use our tool to filter by symptom and help diagnose your plant.
Hemp Russet Mites Hemp russet mites are tiny bugs that attack cannabis plants. In fact, they are so small you can only see them with a magnifier unless there are thousands of them infesting
Kentucky: Hemp Russet Mite Management
During the last 2 weeks of July, several hemp samples were received and evaluated by specialists at the University of Kentucky (Lexington and Princeton). Hemp russet mites (Aculops cannabicola, Acari: Eriophyidae) (Figure 1) were observed on nearly all of the samples. Mite infestations originate in the greenhouse and outdoors and can become a serious problem for hemp growers when population outbreaks occur.
Description of feeding damage by hemp russet mite
In greenhouse settings, small populations of hemp russet mites can go unnoticed. However, when populations increase, curling leaf margins can easily be identified (Figure 2, see older leaves) – similar injury can also be caused by broad mites (Tarsonemidae), which will be discussed at another opportunity.
When population outbreaks of russet mites occur in shoots, and developing leaves, they appear brown or golden colored (Figure 2). Later, the foliage may become brittle and break easily at the petiole. Hemp russet mites can also affect stems, causing bronze discoloration.
Dr. Whitney Cranshaw, from the Department of Bioagricultural Sciences and Pest Management, at Colorado State University wrote that “the most serious damage by hemp russet mites occurs to maturing buds/flowers of all-female clones grown for CBD production. Extremely high populations of mites may build in late summer which damage these tissues and reduce yield and quality”. The latter may happen in Kentucky.
Description of hemp russet mite
Hemp russet mites are quasi-microscopic organisms that belong to the Eriophyoidea. They are not visible to the naked eye unless you use lenses with high magnification, and even with stereomicroscopes they are hard to separate from the secretory glandular hairs on hemp leaves (Figure 1).
Hemp russet mites have an elongate/oblong shape, and females can be approximately 195 to 210 µm long and 62-70 µm wide (Figure 1). Within the eriophyid group there are several plant feeders in different commodities.
They include the russet mites affecting pepper and tomatoes, the apple rust mite, the cereal rust mite and the citrus rust mites. To our knowledge, hemp russet mites feed only on hemp plants, no other hosts have been reported.
Figure 1. Female hemp russet mite in the lower leaf surface of a hemp leaf. Approximate length and width measurements are shown in microns (0.0026 by 0.008 inches). (Photo: Raul T. Villanueva, UK)
Figure 2. Damage caused by hemp russet mites on leaves and shoots of industrial hemp. (Photo: Raul T. Villanueva, UK)
Biology of hemp russet mite
Although its life cycle is not completely studied, the life cycle of hemp russet mites can be similar to other eriophyoids, and may complete its life cycle in 7 to 10 days depending on environmental conditions. Eggs hatch in 2 days, and a larvae occur 3 days later; they may molt into nymphs.
Both larvae and nymphs are similar to adults, but smaller. Instead of having eight pairs of legs as most of the Acarine (spider mites or ticks), all immature and adult stages of the hemp russet mite are four-legged. Females may live up to 3 weeks and lay 1 to 2 dozen eggs.
Management of hemp russet mites
Villanueva (one of the authors of this note) had worked with the apple rust mite and citrus rust mites in Ontario, Canada and Florida, USA, respectively. In both cases (apples and citrus) predation of rust mites by phytsoeiid mites was difficult to detect. Some of the phytoseiid species tested did not prey on citrus rust mites even when they were starved. Other studies had shown similar results.
AgFax Weed Solutions
In the majority of cases, phytoseiid mites are released to control spider mites. Also, it is important to notice that there is a fine balance to manage insects and mites in many crop systems. Hemp farmers need to have this understanding when considering mangement strategies.
For example, when some neonicotinoids and pyrethroids insecticides are used to control aphids or whiteflies in greenhouses or outdoors, several studies showed that spider mites increase their fertility (a phenomenom called hormoligosis).
Studies on citrus rust mites in Florida and Israel shown that the interruption of broad spectrum pesticide applications for more than 3 years may increase populations of predacious mites. In industrial hemp, making judisciuos use of pesticides may be an effective tool to reduce hemp russet mites.
As industrial hemp is a relatively new legalized crop, many miticides utilized for specialty crops or field crops have not been registered in Kentucky. Currently the Kentucky Department of Agriculture (KDA) has a list of pesticides available for control of insects, mites, weeds, and diseases. This list can be found on the 2019 Pesticide Products Registered for Industrial Hemp in Kentucky.
Currently, there are only five miticides registered in this list (Table 1). All of them are products based on oil extracted from some plants. The effectiveness of this product for hemp russet mite has not been tested by the authors; however oils are used to reduce eggs and spider mites. These products should be used following the recommendations and rates indicated in by the manufacturers.
Table 1. Miticide availables for industrial hemp growers in Kentucky. (2019 Pesticide Products Registered for Industrial Hemp in Kentucky). Click Image to Enlarge
Kentucky: Hemp Russet Mite Management During the last 2 weeks of July, several hemp samples were received and evaluated by specialists at the University of Kentucky (Lexington and Princeton).