SPIDER MITES (Tetranychidae)
Spider mites are a cannabis grower’s main pest. Spider Mites pierce the leaf tissue to get at the chlorophyll. The first thing you need to know about them is that they like a dry environment. Which means that if you spot them, you can try increasing the humidity of your greenhouse with generous spurts from a misting bottle. Try this for a few days, and see if they are still a problem. Because mold thrives on humid conditions, you want to make sure you don’t have any harmful mold, like Botrytis (Gray Mold), growing before trying to increase the humidity.
NATURAL ENEMIES OF THE SPIDER MITE
Stratiolaelaps scimitus (Hypoaspis miles) goes after Spider Mites in the soil.
If you’ve previously had a problem with Spider Mites, then release Stratiolaelaps scimitus when preparing your grow area. Otherwise shortly after planting your seeds. And again if you notice that, despite your best efforts, Spider Mites have arrived anyway.
Before they have plants to feed on, Spider mites hide in protected areas. As a preventative, Stratiolaelaps scimitus should be applied on the floor, where table legs meet the floor. Also on the floor around the perimeter of the room. Spider mites will also hide out at electrical and plumbing outlets, as well as where support beams meets the wall. All these spots should be attended. If your initial preparation didn’t keep them away, then, in the early stages, you can apply again, but taking extra care to get Stratiolaelaps scimitusinto nooks, chips, cracks and crannies. If you have a problem already, then release Stratiolaelaps scimitus in the soil.
Amblyseius fallacis is a good preventer of Spider Mites. Amblyseius fallacis is to be used only when you don’t have a serious problem with Spider Mites. It will hang around, spreading itself evenly throughout the greenhouse.
If you’ve had Spider Mites before, then establish Amblyseius fallacis at the beginning, before planting. 2 mites per square foot should do the trick.
This Spider Mite predator can be used with Amblyseius fallacis. They won’t get in each other’s way. Phytoseiulus persimilis likes Spider Mite webs, while Amblyseius fallacis doesn’t. Because Phytoseiulus persimilis like webs, it’s an ideal enemy of adult Spider Mites.
If there’s an outbreak of Spider Mites and webbing occurs, then Phytoseiulus persimilis is your friend.
Mesosiulus longipes (pronounced lon-gipes)
Mesosiulus longipes is another good Spider Mite predator, which may be better suited to your grow environment if it’s fairly dry to begin with. They handle lower humidity, which is what Spider Mites like. But Mesosiulus longipes needs more humidity as the temperature rises. So keep your greenhouse warm, use artificial light and apply 3 Mesosiulus longipes per square foot for a week and then again the next week. That should be enough.
Californicus (Neoseiulus californicus)
Californicus is a useful predator of many mites. It’s particularly useful for the control of Spider Mites, which like dry environments. But so does Californicus, and it can cope with different temperatures. Although, if it has to choose, it, like most Californians, will choose warm or hot weather.
If you’ve seen a few Spider Mites and are expecting more, then get your Californicus out there right away. They like a generous population on which to feed, and, Spider Mites taken care of, are likely to hang around and eat pollen until more Spider Mites show up.
This helpful predator will deal with many mites. It’s got a specific taste for Broad Mites, Hemp Russet Mites and Spider Mites.
Release Amblyseius andersoni early, when Spider Mites are just showing their presence; that’s when Amblyseius andersoni is most helpful.
You’ll get your Amblyseius andersoni in either a shaker bottle or sachet. The bottle makes it easy to carefully release Amblyseiusandersoni onto the plants, close to the flowers. You’ll want to let out 2 or 3 Amblyseius andersoni for every 10 square feet of greenhouse.
Keep sachets out of direct sunlight and use 1 every 2 meters along a crop row. release on the plant, on whichever leaf or twig suggests itself. A sachet should work for up to 6 weeks, but can last a bit longer if Amblyseius andersoni become properly established.
Galendromus occidentalis, another native Californian mite, can be useful to the grower who’s noticed Spider Mites becoming a bigger problem. Galendromus occidentalis doesn’t feed on eggs, but likes nymph and adult Spider Mites. It also likes other mites, including Hemp Russet Mites. It can handle environments of 40% humidity and below.
Release Galendromus occidentalis when you see the Spider Mites. 2 or 3 per square foot should do it. Do this twice a week, and keep in mind that these Californians need 11 hours of sunlight a day.
A family member of the ladybug, Stethorus punctillum is a very small black beetle. These little friends could be your most valuable ally against dreaded Spider Mites. They find populations by smell, and fly between plants. They handle dry conditions and are ideal if the Spider Mites are getting out of control and you’re having problems regulating greenhouse temperature. They also leave eggs at the scene which will hatch and keep working against the Spider Mites. They are susceptible to insecticides, so they’re best used when you’re not using chemicals.
If there are lots of Spider Mites, immediately release 1 Stethorus punctillum for every 10 square feet of greenhouse. You can reduce the ratio by 10 if Spider Mites haven’t become a real problem yet.
Preferal can also be used against Spider Mites. It can also help with Broad Mites, Hemp Russet Mites, Eriophyid Mites, Whiteflies, Thrips and Aphids. It’s made from a naturally-occurring fungus, Isaria fumosorosea, which is delivered via blastospores for fast germination. The spores stick to insects, then germinate and penetrate through their skin, continuing to grow inside. This kills the insect and more spores are released to do the same to other insects. Preferal won’t harm the good pests, or at least it’ll do very little damage.