At CannaBiz gatherings in Northern California and online across the Internet, panicked growers are asking: “Who ARE Those Guys?” as a seemingly undetectable and unstoppable plague strikes fear in the hearts of both indoor and outdoor horticulturists.
Similar to the Tomato Russet Mite (Aculops lycopersici), the Hemp Russet Mite (Aculops cannabicola) is so tiny that infestation often goes unnoticed until the damage is irreparable. I’ve personally never had to deal with these bugs, thank goodness, but I’ve gathered the best info I could find for you and sadly, it’s mostly bad news.
You’ll see exaggerated claims that these mites are so small you need 200X magnification to see them, but that’s just not true, a 14X Loupe is all you need. This is one reason why I have urged you in previous blogs to carry and use an inexpensive but highly effective LED Illuminated 30X Jeweler’s Loupe, or even a hand held mini-microscope on your daily inspections. For five bucks you can’t go wrong with this magnifier and no one is compensating me for promoting this, it is the same device which was standard issue for the Master Gardener training program I went through last year here in California.
Hemp Russet Mites begin feeding on lower leaves and eventually work their way to the top of the plant, including flowers. Early signs of distress include progressive curling and drying out with bronzing of leaves and stems bottom to top. This is often ignored as just a bit of water stress or nutrient deficiency. Those leaves are sucked out and done, yesterday’s dinner, that’s not where the mites are now. Go up a level and microscopically inspect both sides of a few leaves directly above the damaged, unhealthy looking lower foliage.
As with Spider Mites, the warmer and drier the weather, the faster Hemp Russet Mites reproduce. Predatory Mites should be introduced as a natural preventative if Hemp Russet Mites or Spider Mites are known to have been a problem in the past. Any infestation will quickly weaken, wither and ruin Cannabis. Insecticidal Soaps and Herbal Oils are a waste of time and money against Hemp Russet Mites. Prune away, quarantine and safely dispose of any early isolated infested material; don’t be shy about sacrificing a few leaves, Colas or even an entire plant for the sake of your remaining crop.
Outdoors, Sulfur Dust and Wettable Sulfur will kill Hemp Russet Mites during the vegetative growth phase and is safe so long as no oils such as Neem are used for a few weeks before and after the application. Sulfur is generally considered an Organic friendly substance, but don’t use it once you are flowering the crop. Indoors, use a Sulfur Burner, but remember that the fumes of burning Sulfur are quite hazardous to humans; safety first!
I’ve seen a few wacky sounding “home remedies” on the Internet for battling Hemp Russet Mites and I’ll share two of them with the caveat that these methods are hearsay to me and untested. One grower claims to have killed Hemp Russet Mites by enclosing the entire plant in a large plastic bag, filling the bag with pure Carbon Dioxide, and leaving it to suffocate the bugs for several hours. A second and even more dramatic home remedy I found was to plunge the entire plant into an ice water bath, I’m guessing for no more than a few seconds to a minute or two. Got a method that works for you? Please leave a comment below.
Indoors, exclusion is the best preventative. Quarantine new plants, disinfect tools, use HEPA filters on incoming air ducting; generally respect the cleanliness and integrity of your grow space like a medical clean room. Consider soil-less, hydroponic grow methods to reduce the chance of introducing Hemp Russet Mites.
If you have the proper permits, you can use Abamectin on tomatoes to kill Russet Mites but “Sorry Charlie”, this level of chemical warfare while okay on food is a major No-No for Cannabis most anywhere. In Oregon for instance there is a Guide List of what may be applied, and Abamectin is not on the list. You may have heard recently that a pesticide popular with Organic Cannabis growers, Guardian Mite Spray, whose label listed only natural organic active ingredients such as cinnamon oil, was ordered to cease all sales when a lab discovered Abamectin in the mixture. No wonder it worked so well against Hemp Russet Mites, how convenient, eh?
So wait a darned minute, if chemicals like Abamectin are fine to use on produce, why not Cannabis? Because it is “Medicine”! Remember how we got here? Personally I think what is needed is a two-tier system, a state by state and eventually a national standard for Organic Cannabis certification for producers that want to go the certified pesticide-free medical route, and then another more relaxed, food grade set of rules for those who want to grow, distribute and market into the not-medicine retail trade. I have a nagging suspicion that some politicians may see super strict pesticide residue level rules as a way to effectively re-impose Cannabis prohibition, just sayin’.
Then there is the hairball of soil or “sun-grown” based organic versus hydroponic pesticide-free. Many Organic folk insist (without peer reviewed University research level scientific proof) that soil-less growing can never be as potently healthful as soil based due to the absence of beneficial mycorrhizal fungi and therefore hydroponic grown plants must not be labeled “Organic”. So, to keep the Organic folk sleeping peacefully at night we’ll have to introduce a labeling system that differentiates between soil grown organic and pesticide-free hydroponic.
As the Cannabis growing business comes out from the shadows, let’s hope the big money interests don’t muscle out the little guys who paved the way. We need the financial community to step up and offer the protection of Crop Insurance and futures hedging instruments to help modern Marijuana farmers get through bad times. Ask any Iowa sodbuster about droughts, pestilence and international politics driven corn market price fluctuations and their impact on multi-generational family land legacies.
Disclaimer: Any advice and opinions offered about the cultivation of cannabis by Bruce N. Goren are his own and do not represent the University of California or the Master Gardener Program.