I agree with using Permethrin or pyrethrin but if you use just that you will be spraying for the rest of the summer. For each gallon of spray make sure to use the maximum amount of the poison and add 1 Tablespoon of Dawn dish washing liquid. And most important of all before adding the Dawn or poison put 2/3 cup of food grade diatomaceous earth in a jug with part of your water and shake it well then strain it through a fine mesh strainer into your sprayer then add the remaining water, the Dawn and the poison. Shake your sprayer and pump it up as high a pressure as you can and spray all parts of the plant especially the undersides of the leaves, the stems and the ground or mulch under the plant. Wait three days and remove any dead or dying leaves then repeat this spray again. The poison gets the adults it hits and the soap helps coverage and in penetrating the webbing. The DE will remain on the plant killing juveniles that hatch out from the multitude of eggs that mites lay. Adding the food grade DE really cuts down on the number of times you will have to spray your plants. It is best to use this concoction late in the day near or at sundown for the benefit of any bees you may have.
This is the only thing I have found that is effective in stopping a big infestation of spider mites. You still might lose a few plants that have become infected in the new growth but most will recover with time. Once you use this method be ready in the future to use it again but just as soon as you see that stippling of the leaves indicating that mites are present even if you don't see them. Once you see webbing it indicates a fairly bad infestation already even before leaves start to brown and die. Every day you wait to treat them is increasing the problem and the damage that they are doing to your plants.
Good luck. I went through the worst mite problem I have seen in over 40 years of growing tomatoes. I usually see them at least once each year but last year was off the charts.
Bill
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