Russet Mites: A need-to-know guide for a microscopic enemy

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Aculops cannabicola, or the hemp russet mite, is striking Washington cannabis growers hard this year.  Numerous growers are fighting off these tiny pests, and they are spreading like a plague of locusts.

The most frightening fact about these pests is that they are not visible to the naked eye.  The size of these guys ranges from 20 to 170 µm long and up to 65 µm wide.  To give you some perspective on that, they are smaller than dust mites and thinner than human hair.  Russet mites are so small they can actually be distributed to neighboring areas via wind- which is a big concern in Eastern Washington!  They’ve even been known to hitch rides on other insects to spread to new areas!  Russet mites can hide in contaminated potting soils as well, or can be introduced by bringing in clippings and clones of infected plants.  Don’t assume you are safe from this pest just because you are operating an indoor grow.

Being microscopic means that many farmers don’t know they have a problem until their crop has been affected.  Suddenly your bacteria counts start spiking and your potency starts dropping, but you haven’t changed anything and don’t see any obvious issues.  You don’t know why or what’s going on until the mites get so bad the plants themselves start telling you something is wrong, and even then the issue might not be obvious- you start wondering if you have a mosaic virus, a nutrient deficiency, or other form of plant stress.

The visible symptoms created by the russet mite are very similar to other common problems.  Fan leaves might curl a bit at the edges and have a glossy wet look- similar to heat stress.  Leaves may have yellow or bronze spotting – sometimes also a symptom of mosaic viruses.  New growth may come in twisted and seem stunted/limited or leaves might droop – as if the plant is suffering from environmental stresses or nutrient deficiency.

The females over winter inside plant stems, where branches join main plants, and sometimes in root structures.  The mites are sap suckers. They start by feeding on the lower structures of the plant, then work their way up as the food supply is depleted.  Russet mites are especially attracted to flower resins and can go unnoticed while feeding in flower structures.

To check for mites, you’ll need to purchase a magnifier that is at least 14x, preferably slightly higher than that.  Most jeweler’s loups will do the trick.  Next find an area slightly above where the plant is showing stress. If the plants are not yet showing stress, start checking towards the lower portions of your plants. Be sure to check in several places if you don’t see them at first.  The insects don’t stay in the same area after they’ve fed and will move to other areas on the plant.  Be sure to check thoroughly before you decide you are in the clear.

So you found mites, now what?  There are a variety of pest management strategies available.  Regardless of what strategy or combination of strategies, be sure to maintain it long enough to eliminate the pests.  Given the russet mite life cycle, treatments can take several weeks before the infestation is eliminated, and, because the mites easily spread through wind, vigilance is required to prevent re-infestation.  Under ideal conditions, a single mite may live a month (or more) and lay many eggs during that time period.  When the eggs hatch, the cycle starts all over again.

Some of the pest management options available include:

  • Predatory mites and beneficial nematodes
  • Insecticidal soaps
  • Neem oil (if applied at the first signs of infestation)
  • Pyrethrum based sprays (but be wary of how much you use to ensure you don’t exceed WSLCB limits for pyrethrins!)
  • Diatomaceious Earth (won’t get rid of an infestation but will slow down the spread of the mites)
  • Sulphur dust/wettable Sulphur (not to be used on flowering plants!)
  • Pruning infected branches, removing infected plants, and quarantining infected areas.
  • Removing weeds and other vegetation near your crop that could harbor mites.
  • For indoor grows, adjusting environmental factors, such as temperature and humidity outside of optimal range for mite reproduction (remember changes to environmental factors will affect your plants too!).  Cooler temperatures will slow reproduction, but not kill mites.  Mites don’t survive well in temperatures over 105-115 F.  Russet mites prefer drier climates and breed more slowly in higher humidity.

 

This list is by no means exhaustive.  There are numerous brands and types of products out there that are effective against mites.  Regardless of what method you choose, there are two important things to remember:

  1. Make sure your pest management strategy is in line with state law and only includes pesticides approved on the PICOL database
  2. Apply your pest management strategy long enough to eliminate infestation and stay vigilant watching for any future infestations and getting treatment started as early as possible.

45 Comments on “Russet Mites: A need-to-know guide for a microscopic enemy”

  1. Several weeks of spraying M Pedestal we are finally getting control of the Russet Mites but not gone.
    M Pede can be pretty hard on the plants of spraying twice a week sometimes 3 and he only way you will gain ground.
    Tried some cedar oil concoctions and it really kills them but is pretty fatal to the plants too.
    Rumor is WA DOT is spraying roadsides with Russet Mites to help with maintaining vegetation with less mowing etc. If this is true I would imagine we would be seeing a class action lawsuit soon considering the amount of tax marijuana producers and processors are charged then with a declining availability of pesticides that can be used from the Washington LCB

    1. Hey Carson, keep fighting the good fight! Not so sure about WADOT, I did find this article http://www.cannabisbusinesstimes.com/article/the-cannabis-rumor-mill/ which said that “that while those mites (which, again, were neither broad nor russet mites) were being studied, no mites whatsoever have actually been approved for use in highway invasive species control in California nor any neighboring state.” Hopefully if something like that DOES happen we’ll find out about it beforehand, it would be a big deal for sure!

  2. I destroyed all plants and cleared out my entire room, took lights down and cleaned them along with everything else ezcloners etc. It has been a few weeks now that the room has been shut down. How long until it is safe to reintroduce plants into my room given everything has been cleaned and all infected plants removed? Thank you

    1. Hey Keith – you’re probably fine to reintroduce them now. Fresh soil, pots, etc is a good idea. In the outdoors the russet mite eggs are viable through the winter, so any microscopic eggs hiding in a pot that you try to re-use could hatch and start it all over again.

    2. Use Gard N’ Clean F, gaseous chlorine dioxide to sanitize your area and the containers you use. It is an off-label use, but it works, even during flower and leaves no residue, but you have to completely exhaust the gas before you go back into the area.

    3. Yeah I had to do the same thing kill all my young ladies it was very devastating clean my rooms give a entire month before you even attempt to cultivate again that’s about the only way to be sure there’s no more russet mites alive now here it is six months later I finally got my first harvest that’s my russet mites attack

      1. So waiting a month worked? I’m a almost around the 1 month mark as well. It destroyed my harvest before but I only waited 2 weeks before starting another hoping that’ll be enough time. These things suck lol

  3. “Ah” the wonders of arthropod evolution. How amazing it is after all these years to see the cannabis industry facing the same agricultural problems as other crops. As any farmer knows, the pests keep adapting, and we keep fighting back. It’s a battle that is unlikely to end, so we must treat , and beat.
    It’s a long lasting war of attrition. Sterilize, wash, filter, spray, test, observe, and innovate “TOGETHER”, or we will all sink together.

  4. I believe there are 3 species of russet Mite approved for use. And I know that Oregon has used russet mites in the past fairly common practice among Department of Transportation in some states from the research I’ve seen.

  5. thank the lord I created a recipe that actual WORKS!

    Russets have no Brain, too bad for them I do!
    My formula seems to have the ability to deny’s the lil-bastards any opportunity to use their mouth parts to suck on my plants. I need a lot more study under higher magnification than 100X to observe exactly all the action’s my formula accomplishes when sprayed. I’m excited with the fast results though.
    I have a 48 plant medical organic garden in OR. Found russets 3 weeks ago(2 weeks into flower) & about cried, …damm-it. Of course I googled practically everything written on the subject, 99% of which is proven won’t work to eradicate the scum, “Tough Cookies” they are, & build immunity to even nasty pesticides very quickly it seems.
    I got this recipe from my Grandfather to be honest back in the mid 1960’s & have used it for other pests for the past 40 or so years, …for my girls & veggie gardens alike, flowers, lawn ect.
    I have amended his formula somewhat, but I’m still using only ingredients I normally, already use in my Cannabis garden yearly w/one exception, & that ingredient came from my Kitchen.
    I put a test batch in a spray bottle & sprayed 1 lower branch on my worst infecter plant to start, & was blown-away by the effectiveness overnight, I closely watched under 100X scope for a few days as they were dying off that branch Wholesale, their helpless squirming was delighting & relieving me at the same time, I next sprayed the whole plant(A Sugar Titan) & saw it come back to life & new bud growth within days, daily counting the ratio of dead bugs VS live/moving bugs & knew right away I have a WINNER. I doused all 48 girls the next day, I was & wasn’t surprised to see the results, I sure was surprised to see something working to actually Kill them so off fast, like nothing else I’ve seen or read about working, I wasn’t surprised to see that my Brain out-do their Non-Brain.
    Within days they stop crawling & die, the egg’s appear to soak up the spray, turn milky & seem rendered unable to properly hatch out, or they die soon after, not being able to move around very well or Feast on my girls at all, the juvenile death rate was outstanding, the adults turn a tan/brown color, then die, they seem to crystallize after they are dead, clearly & visibly DEAD!
    I am looking for these Clowns to be ALL gone within 4 more days after my second application tomorrow, So….after 4 days, … & being sprayed 1 time, I have a 85% death rate at least, I’m trying not to overstate my results, but I think I’m really above 95% kill rate so far & my plants don’t seem bothered one bit, in fact they are reacting in a fully positive manner, rebounding w/NEW growth & it looks like the resin production has also been stimulated/boosted, but more studies will be needed to determine if that is in fact a side effect of what I’m using to defeat this menace to us all.
    I do have Jorge Cervantes quite curious, & Big Jim Matthesson (breeder/inventor of “Grape Ape”, & a Cannabis Cup Winner)in my corner, however I can’t/won’t truly claim Victory just yet, …the best part is I’m not worried 1 bit that my bud’s will not pass testing either!
    “The Bottom Line” ….Keep the Faith, if it be Me or not, someone will Win this battle!
    If at all possible, I will bring this knowledge to Market in a usable product 2019, & it won’t cost an Arm & a Leg either, that’s almost the worst part of the fight, we need a/the right-priced product we can all agree “WORKS” …BECAUSE IT DOES!
    NOTE: I made 100 gallons(about 2 gallons per-plant) at a cost of just under $100 in my purchase @ Wal-Mart, that sounds a lot better than $230 for a gallon of stuff that makes 32 gallons of spray, …”THAT DIDN’T KILL ON CONTACT as they claim”! ….jus-sayin

    1. Hey! Don’t tease us! If you are gonna comment that you have a valid russet mite killer method, you should tell us. Personally I’ve seen the best results with liquid sulphur. I use Safer brand “garden fungicide” which is straight sulphur and nothing else at 120 mL per gallon. And it’s the bomb for keeping away PM as well. I make it my last early flower spray in week 2/3 flower and the residue stays on fan leaves and seems to help a lot preventing PM. Anyway, I’ve seen it kill russets. With Russets you gotta get good at using a 100x microscope . You HAVE to learn to spot them. Creepy little buggers. The day after spraying full strength sulphur , you will find dead ones

    2. Don’t tease! If you got something to share, share it! Should be easy if you bought the ingredients at wal mart, share the knowledge brother!
      I found the best cure to be Safer brand liquid sulphur at 120 mL/gallonwhich makes it 3$ per gallon of spray. For a 120 sq. Room , it took me 2 gallons of spray. Currently I use it as a preventative. And it’s great to prevent PM. There are a few other sprays that help, but sulphur kills them. Ya gotta get good with a hold held microscope and learn to spot them. Spray and then find them dead. Now repeat.

      The old school boiled sulphur (it’s a red/orange color liquid) is also very effective but I find it a little harsher on the plants and it isn’t approved for use in my state but it should be. Back in the day farmers made it themselves

    3. Hello!! I’d love the recipe!!! You could charge me for it.. PayPal..!!

      I’m definitely interested in a spray that works like this… thank you!

      Patty

    4. It’s been a couple years since you posted that you had found the answer. I haven’t seen anything nearly as effective as you were saying what you came up with is and I interact with a huge number of professional cannabiculturists.
      Skunk pharm research Consulting is willing to sign a non-disclosure/non compete agreement to test it and, if it works as you say, to arrange the financing necessary to get it licensed and bring it to market.

  6. Would love to know what you’re using is so I could help my garden out I’ve been battling these little bastard for a year-and-a-half and just now today figured out that there russet mites. I have an indoor medical Garden in Michigan 40 plants. Would love to know what you’re using please help me out. Thanks a lot Scott

  7. People use micronized sulfur. 2-3 table spoon per gallon with wetting agent. Spray in 3-4 day intervals. They will be dead and not return. Don’t spray in flower past week 2

  8. The answer is extremely simple and it’s the same answer to all cannabis pests, molds and mildews… neem oil foliar.

    Accept nothing less than Pure, cold-pressed neem. At a rate of 1/2 tbsp/gal, emulsify the neem oil with 3-5 drops/gal of dr. Bronners soap. Add water to emulsified neem/soap and spray during dark period (preferably 2 hours before lights on).

    Apply every 2-3 days for active infestation of anything. ANY. THING. Apply once a week as a preventative.

    Neem has an extremely short half-life and can be used into the last week before harvest. Some folks online have said they “tasted” neem in their flowers…they likely didn’t use real deal pure cold-pressed neem and they are tasting some other contaminant.

    All you’ll taste is dank if you stick to the neem foliar. Good luck and much love!

    1. hi, i read your comment about using pure cold pressed neem oil for russet mites. so its ok to spray right on the flowers even up to 1 week before harvest?
      I have an infestation and I’m in week 4. predator bugs arent keeping up and the russet mites are still spreading. thanks!!

  9. I use those yellow sticky pads 2 monitor the guard look on those strips or those sticky pads with the magnifying glass and maybe you can catch an infestation early

  10. how long can russet mites live in the soil if there are no plants present? I want to continue to use my soil. I have eradicated all plants, bleached everything applies soil predators (rove beetles, Stratiolaelaps scimitus, nematodes ). im am going to spray some prf97 on the soil as well. How long can a mite live without a food source in soil ? How long may an egg stay viable in the soil? i’ve added a fresh mulch layer introduced predators and a fungal inoculant. I dont want to give this soil up

    1. I’m wondering if you learned an answer to this question? I’m also an organic gardener and of course I lean toward not wanting to reuse soil which had a plant covered in russets, but if I could learn more about the actual lifecycle of these creatures it would be helpful. They are very tiny soft bodied insects with I’m assuming quite a short lifecycle so if they are deprived of food they shouldn’t last too long? I’ve read they lay eggs in the stems in order to over-winter, so theoretically if I remove all the roots from the soil, toss the top layer of soil, and then compost the soil for a few months in the pots and let the worms and other micro organisms work their magic I’m pretty sure they will be gone. That’s what I plan to do with soil from other plants where I didn’t find russets. But for the few plants that actually had them, I will probably donate this amazing soil to some outdoor garden spaces where hemp is. It going to be grown…

  11. I have had success getting rid of russet mites and spider mites by making a ‘concoction’ of some of the hottest peppers you can find in grocery store, hot pepper flakes, about 4 tblspoons of crushed garlic (has natural oil that helps it stick to plant/kills bacteria and viruses too), cayenne pepper or extreme hot chili powder with a pot of water. boil this mixture for about 30 minutes, then simmer for 4 hours. let cool, strain. keep in refrigerator. i usually fill about a 1/3 to 1/2 of a spray bottle with the solution and the remainder water. i spray the whole plant, soil, stems, upper and lower leaves.. until dripping with this solution. careful, it will burn your eyes and make you choke up.. so mask, gloves and goggles.. when i did this the first time i thought it would kill the plants. nope, they flourished. probably because this hot stuff kills off the eggs and mites. burns their soft layers. and it makes the plant really hot to eat if you have other pests. you can use some SM-90 in it to help it hold on to plant. I would do it with out the lights so not to cause any ‘burning’ from light source. and use it say every 3-4 days. keeps all pests at bay and doesnt hurt plant. dont use on buds.. will affect taste. besides if you use this on your plants in veg you shouldnt have any pests during flowering.

  12. Hello,
    I am a technical services rep for Southern Ag. The number of calls from Cannabis growers asking for help is increasing. Today a grower said he was loosing over 100 acres of hemp because of this pest. I had no answer that would fit within the constraints of pesticide regulators.

    Most on line recommend predatory mites. Unfortunately natural predators are not the best hunters. It’s nature’s way to prevent them from wiping out their food supply. Increasing the number of predators high enough to control russet mites is very expensive and your results are sometimes unreliable. IMO Predators work very well but timing is everything. If the crop shows symptoms, it’s too late for predators.

    In regards to Neem this information may be helpful. Neem Tree (Azadiracta Indica) seeds contain the highest concentration of oil. The extraction process [for pesticide manufacture] splits the seed-oil into 2 components: Azadirachtin and Neem Oil (“Clarified Hydrophobic Extract of Neem Oil”). The cold processed “raw” neem oil is not split, so the Azadirachtin in cold processed Neem remains. This is probably why it kills more mites than “regular” Neem Oil by itself. [The Azadirachtin kills most of the mites.]

    Biopesticides that contain Azadirachtin are economical, effective, less phytotoxic to blooms and best of all they are approved for Cannabis. If you decide to try it, add a surfactant to enhance coverage and effectiveness. Avoid the temptation to use soap. Commercial surfactants are cheap, consistent and very effective. There are many brands of Azadirachtin based insecticide/miticide and almost all are labeled for cannabis. See the link at the end: Pesticides for cannabis published by the Oregon Dept of Ag on August 6th 2019.

    You also might apply something to quickly weaken the mites first. For example spraying an oxidizer prior to neem. Products such as Oxidate [peroxyacetic acid] are OMRI and labeled for plants. This will burn up diseases and viruses and severely weaken or kill insects and mites. The next day apply insecticide and perhaps a biofungicide like Double Nickle LC if disease pressure is high. Two applications should nuke them.

    I hope that helps.

    ODA link: https://www.oregon.gov/ODA/shared/Documents/Publications/PesticidesPARC/GuidelistPesticideCannabis.pdf

    GPM Neem Oil explained: https://gpnmag.com/article/explaining-azadirachtin-and-neem/

  13. sign of Mites shown as early as a week into flower but we were negligent. Now I am chunking out my best strain and I have curling brown water leaves Brown hairs, and now full on nugs going complete mush haven’t brought out a magnifier yet but I’m certain it’s russets as my lady bug pop has been taking off as of late. What’s best advice you could kick down to young farmer that needs to be wacking and tacking grippin and rippin basically everything in 3 full weeks at the latest. I refuse to bring the mites with me from the field to the rooms I have 3 weeks help me save this year and my young company…..An elephant never forgets…

  14. does anyone know how long russet mites can live without plant material? i’m recovering from an indoor small grow infestation. they may be tomato though, not hemp. i’m not really sure. all plant material in the entire house is gone, including house pants. tents were heated to 120 degrees. wiped down with alcohol. i’m sure over time they got all over the house. so i’m trying to wait them out and am not sure when it would be safe to go back to growing. any insight would be greatly appreciated. many thanks in advance.

  15. I used powdered Azasol (the azadirachtin from Neem oil), and some hydrogen peroxide 33%, 1 drop of dish soap, and even some isopropyl, all mixed into tap water.

    then i sprayed with just hydrogen peroxide and alcohol mixed in water the next day to clean the plants

    i also walked around with a 10 watt UV-C mercury bulb and held it 1 cm or closer on plants while never stopping movement or hitting them over 1 minute until i walked all around rooms and stuck bulb among all the plants.

    then the mites didn’t seems to want to eat the plants, or survive the washing sprays, but then they came back if the treatments werent kept up.. took less than a month!

  16. I am convinced there is no solution to russet mites during flowering. I found them early but they just keep going with the use of neem early, then nematodes and stripping of the contaminated flowers, no success it is a slow and painful loss.

  17. Rasta-Rog Is your stuff on the market and what is it called? I’ve used everything including the garlic, pepper concoction..treated 3 times and them mites still moving! Much aloha if you can tell us your secret or where to purchase?

  18. I’ve found that the cheapest and most efficient method to manage hemp russet mite during flower is hot water sprays. I have successfully eradicated rice root aphids using hot water sprays/drenches. The goal is control the moment that you’ve scouted them. Cannabis plants can withstand hot water drenches up to 120 degrees, not to exceed 5 minutes. Sick or weak plants may not survive, so please keep this in mind when treating with hot water. Hemp russet mites will die on contact when sprayed/drenched at this temperature. Micronized sulfur works as well and provides protection up to 2 weeks and its inexpensive. Bonide is an affordable brand and very readily available.

    Good luck!
    Peace and Blessings!

    1. I’ve hear good things about Sulfur. How many TBSP of Sulfur per gal and do you add surfactant? These little bastards are frustrating as hell to deal with!

  19. We found russets about 3 weeks before harvest as one plant was chowed on from bottom up. They spread initially. We hit them with NukeEm. Organic approved. We hit them hard. It worked! Still some work involved.

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