Of the dozens of different plant parasites which may plague an indoor garden, one of the most infamous, talked about, and feared is Tetranychida urtica — more commonly known as the two-spotted spider mite, or red spider mite. As luck would have it, these arachnids are also among the most common pests in indoor gardens. They are found everywhere. Native to Eurasia, they can now be found worldwide, particularly in controlled agriculture settings.
An infestation of spider mites can lead to a host of garden problems. Even a few mites can lead to increased plant stress and thus decreased plant health and yield. Affected leaves will be stippled with white. These white spots are cells which a mite has pierced, fed upon and killed. Leaf margins and tips will often curl down and inward, concealing and protecting the mites and their eggs.
A close inspection of the undersides of such leaves will often reveal a small amount of webbing containing perhaps dozens of tiny, white, spherical eggs and minuscule, translucent yellow, red, or brown to black mites.
Although the mites' initial assault may seem innocuous, their tiny size and ability to reproduce very quickly compounds the issue. As the pests themselves are difficult to spot, a gardener can easily miss the subtle signs of initial infestation if he or she does not closely inspect their garden each day. A less vigilant gardener might overlook these signs until leaves are already yellowing, dying and dropping off and the plants are covered in highways of webbing, not to mention hundreds or thousands of very mobile, very hungry mites.
So, we get that spider mites are common, elusive, and destructive. How do we get rid of spider mites? Or better yet, how do we prevent spider mites from infiltrating our gardens in the first place? If you are diligent about prevention, eradication may not be necessary.
Mites are generally brought into the garden by none other than the gardener himself. Out doing yard work before tending to your indoor garden? Mites can ride in on clothing, hair, or any outdoor materials you bring in with you. For this reason, it is important to ensure that your clothes, hands, hair, etc. are clean before entering your garden space. As a gardener we know once said, "I get right down to my skivvs before I even set foot in my garden!" I'm sure he feels liberated, too, but more importantly, his garden is virtually pest-free.
We often hear gardeners complain, "I didn't have spider mites until I took these clones from my friend/brother/sister/Airedale, but he/she said they were clean!" Maybe they were clean and mites were introduced another way, but this "coincidence" is all too common. We've discussed how minuscule and easy to miss mites and their eggs can be, but it is also important to know that mites can lie dormant when conditions are unfavorable, only to re-emerge when they think they may have a better chance at survival. When receiving any new plants or cuttings, keep them in a separate quarantine area for the first week or two. This will keep any pests away from your garden while you watch carefully for their appearance on your new cuttings. Check daily for any signs of pests like those shown in the images above, and treat if necessary,
In a perfect world, we would never have to treat for mites. Many of the gardeners we talk to are currently fighting a mite population (again), or recently were. Most, if not all, have at one point or another. Let's run down some of the control methods and their varying effectiveness.
Yes, showers. Running water and running water only, maybe with a drop or two of Dr. Bronner's or dish soap. Say you've returned to your garden after a weekend away. Your plants are all good on water and nutes; no one has grown into the lights. Things are looking good, save for the webs and mites covering the canopy. Oops. In a situation like this, it can be useful to shower the plants off in order to wash off the worst of the mites and protective webbing. This is not a standalone treatment. You will not be able to remove all the mites and eggs in this fashion. There are far, far too many sheltered hiding places within a plant's canopy. But it's a good start before you move on to the next step.
General Purpose Insecticides
Potassium-based insecticidal soaps and pyrethrins sprays such as Doktor Doom foggers, are widely available and largely safe to use. They serve well as a temporary population control method, with two distinct drawbacks: the mites can quickly build up resistance to such mild pesticides and these sprays do not kill the eggs.
Other, heavier-duty miticides are available as well, such as bifenazate. Most of these are heavily regulated—they may not be applied by non-certified personnel, may not be shipped to or used in certain states, and are incredibly toxic to fish and other aquatic animals. Because of the hazards to people and animals alike, associated with the application, presence, and runoff of these chemicals, we cannot and do not recommend their use, particularly on consumable crops and certainly not in your home.
"Specialized" Spider Mite Sprays
There are many sprays marketed mainly or solely for the eradication of mites. Nuke ‘Em, SNS217, Mite-X, and Ultimate Wash all fall into this category.
Mite-X and SNS217 are oil-based sprays which effectively kill mites and their eggs, and work (somewhat) to repel mites as well. Each works exceptionally well when sprayed as per the labeled directions. Both are exempt from FEPA pesticide labeling regulations as 'minimum-risk pesticides.'
NPK, the manufacturer of Ultimate Wash, lists their undisclosed active ingredients at 0.1665% (comparative to the active percentage in many pyrethrins-based sprays.) They claim that a 'frequency' applied to the water contained in Ultimate Wash renders it a safe and effective pesticide, and it does not contain any harmful additives or chemicals. While I am skeptical of their 'frequency water' explanation, Ultimate Wash is nonetheless very effective at eradicating mites and their eggs.
Nuke ‘Em, despite the ominous name, is also FEPA-exempt, containing only organic, food-grade materials. Despite its innocuous constituents, Nuke ‘Em is one of our favorite treatments for both spider mites and powdery mildew. It is only available as a concentrate, so a small bottle goes a long way!
If more integrated, non-chemical control methods are more your speed, there are several predator species which snack on spider mites that are available commercially. Stethorus punctillums, a small, black beetle related to the ladybug, can consume many mites and eggs daily and can potentially establish a breeding population in your garden. Mites in the Phytoseiulus genus (P. persimilis, P. longipes, etc) are predatory, rather than plant-eating, and will readily consume spider mites and their eggs. Other useful predator mite species, frequently available by mail order, include A. californicus, G. accidentalus, M. longipes, A. fallicus, and N. californicus. Depending on your sources, Minute pirate bugs (Orius spp.), big-eyed bugs (Geocoris spp.) and predatory thrips (Leptothrips spp.) may also be available as control measures.
In conclusion, perhaps the old adage says it best: An ounce of prevention is worth a pound of cure. Prevent! But when the inevitable happens, get on top of it fast. Don't hesitate to contact us with any questions.