Spider Mites in the Garden

Home Grown  by Keith Reed
If calls to the Payne County Extension office this week are any indication, spider mites are here in high numbers, with tomatoes being the crop hardest hit. These pests are difficult to control under the best of circumstances. When spider mites get the upper hand, they can quickly overwhelm the plants they are attacking. In some cases, it is too late to control spider mites by the time a gardener recognizes the extent of the problem.

The key to control is early detection, a critical component of Integrated Pest Management (IPM). Spider mites are extremely small and difficult to detect for all but the most discriminating eye. As with many other insect pests, these critters tend to collect on the underside of leaves, making them even more difficult to see.

Try this handy trick for monitoring spider mite populations. Simply place a clean, blank piece of paper under some leaves (they usually begin to feed on the lower part of the plant) and pat the leaves several times onto the paper. Any mites present will appear as tiny specks. If they are alive, you can usually see them moving. If in doubt, mash and wipe your finger across the paper. If the specks leave streaks, usually red, you have confirmation that spider mites are present. Waiting until you see the characteristic webbing form puts you behind on control measures. The webbing acts as a protectant, making control very difficult.

Spider mite control strategies are multi-faceted. Reaching for the nearest “all-purpose” insecticide and hoping for the best is not a viable strategy. Most insecticides are not labeled for spider mites (they are not true insects) and actually do more harm than good by killing beneficial insects which may be feeding on the mites. See OSU publication E-1023 Conserving Beneficial Arthropods in Residential Landscapes for excellent information on beneficials.

Begin by pruning off heavily damaged parts of the plant and removing them from the garden. Spraying the underside of leaves with a strong blast of water is surprisingly helpful as this physically removes many of the mites. Horticultural oils, insecticide soaps, and neem oil can be effective if applied directly on the spider mites. Read the label carefully as applying these products when it’s too hot can do more harm than good.

Products containing the active ingredient bifenthrin also offer limited control. Look for this product sold under names such as Eight Insect Control- Flower and Vegetable, Talstar, or Ortho Max Bug B Gone. Remember that relying only on these products will result in poor long term results. These pests, as almost all other, will build up resistance with repeated use without incorporating other control measures. Resistance build-up measures are discussed on the product label and are just one more reason why reading and understanding the label is critical to all pesticide application.

Keith Reed is the Horticulture Educator in the Payne County Extension OSU Extension office. You can contact him via email at keith.reed@okstate.edu, call 405-747-8320, or stop by the Payne County Extension Office at 315 W. 6th in Stillwater.

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