Spider-Man, Good! Spider Mites, Bad!
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Q. Tony in Washington Township Gloucester County New Jersey (that would be exit 53 A) writes: "So every year I have the same problem with my tomato plants. The plants grow tall and produce lots of fruit until sometime in August when spider mites attack. I try to control the mites by spraying the plants daily with a high-pressure soak from the hose. This helps but I'm looking for something more effective. If the plants survive August they rebound and start to flower again but I lose three or four weeks of production. My garden is flat earth, but on an incline (it drops about 4 feet in its 25-foot length), south facing and mulched with compost. I only grow hybrids with maximum disease resistance. I was thinking of trying Surround this year. Do you think this will help? PS I have 2 beagles that routinely graze in the garden (cucumbers, string beans and bell peppers are their favorites) so I have to be very careful about what I spray in the garden."
A. Tony: Even those of us who are beagle-free need to be careful about what we spray in the garden, as even some natural remedies can be toxic to bees if those remedies hit the bees directly. And chemical pesticides (gag; choke; gak) are not only dangerous to children and other living things (I just made that up; really), but ineffective against these pests, as studies have shown that spider mites rapidly develop resistance to chemical controls. To which I, as a responsible mature and grownup adult organic gardening authority can only say to Dow, Bayer and Monsanto: "Nah, nah, nah, nah, nah nah!"
Ahem. Spider mites are not spiders of any kind. But they are true mites, which, like ticks and Peter Parker, are arachnids and not insects. They got the prefix "spider" because the female mites spin a kind of distinctive webbing to protect their eggs and/or developing young. They are sap suckers that puncture the leaves of plants and can cause substantial damage, especially in greenhouses and to growers of mari-hooney. In fact, they might be the most problematic pest for cannabis growers.
But they are also known pests of tomatoes, as well as peppers, potatoes, corn, cannabis, strawberries and cannabis. And cannabis.
Anyway, my garden is in the same basic growing region as Tony's Exit 53 A and I have yet to ever see a spider mite, so I am going to first suggest two non-specific remedies. Tony acknowledges that he is a flat earth gardener. Flat earth gardening leads to serious soil compaction because your big feet are always stepping on the soil around your plants. Soil compaction is the second biggest human cause of plant death and/or pest problems (second only to overwatering), so suggestion number one is to build at least a few raised beds as far away as possible from the areas of the annual August infestation and see if that takes care of things. And if it does...
...Build more raised beds!
The second non-direct approach involves fertilization. Tony says he mulches his tomatoes with compost, which is excellent; unless he also uses highly explosive chemical fertilizers like Miracle-Gro and Osmocote, which have been shown to attract pests and promote disease. So if you are using chemical fertilizers, stop!
OK; now, spider mites are creatures that require dry conditions, which makes water a good idea. But sharp streams of water are the cure for insects like aphids (actually, especially aphids); basic high humidity is the cure for spider mites. So rather than the fire hose effect, go for a morning watering of the leaves every morning the day is expected to be hot and dry. No; this is not the ideal way to water drama queens like tomatoes, but we're using water as a deterrent, and we pretty much have to wet the leaves to deter the mites. Just be sure to ONLY wet the plants in the early morning so the sun can hit them and help prevent disease.
And Tony already says that he's only growing disease-resistant hybrids (which is not the best plan; mix some open-pollinated plants in there!), so a little morning wetness shouldn't be a problem.
There are also 'predatory mites' that exist only to eat your bad mites. I suspect they are much more effective in a greenhouse situation, but if you wish to go mano a mano (or more correctly arachnid vs arachnid) maybe buy a bunch and release them when the first faux spider webs you see. If you choose this path, do nothing else or you might kill your good mites.
'Surround' is the trade name for a micronized clay spray that prevents insects (yes, and arachnids) from reaching actual plant tissue and so is an excellent suggestion. There are also the old standbys of insecticidal soap and light horticultural oil. Both of these controls need to coat the pest insect (or in this case, arachnid) to be effective. I urge you to purchase professionally made insecticidal soap, as homemade versions can quickly become herbicidal soaps, which would be bad.
I used to urge people to also buy professionally made horticultural oils, but then I started using PAM on my mud dauber wasp and yellowjacket nests to excellent effect.
But choose one tactic or the other; soap or oil OR Surround; do not mix and match....
Good luck Tony!