Mites like it hot

Have you noticed the leaves of some of your garden plants developing yellow or brown freckles? Or, in severe cases, are the leaves developing a bronzed appearance? You look at the leaves but can't see any bugs, so you begin to wonder whether your plants have some sort of virus.

Chances are, you're seeing damage from the two-spotted spider mite. These little critters love hot, dry weather. They'll suck the sap from your plants and weaken them. To make matters worse, spider mites reproduce at an astounding rate, and large numbers can do serious damage to plants, including murder by stress.

Spider mites are so tiny they're difficult to see with the naked eye. Colors can be yellow, green, brown or red, depending on the season and the particular species. One way to identify an infestation is to look closely at the underside of the leaves. The mites produce fine, silk-like webbing in which they lay their eggs near the leaf veins. In hot, dry weather, the eggs can develop into adults in a week, at which point they begin to increase their numbers even more. A mature female can lay 200 eggs in 10 days, which can lead to rapid and serious plant damage.

But wait — there's more. Plants that are already under stress from drought are even more appealing to the spider mites, as the chemistry of a stressed plant changes. Although spider mites attack many kinds of plants, they seem especially fond of beans and eggplant.

Evergreens host another species of spider mite. As the summer continues, you may find them in spruce, juniper, arborvitae and pines.

The needles develop a scorched appearance and drop prematurely. The mites often turn red as fall approaches, and may be called red spiders.

Spider mites have many natural enemies that feed on them, including ladybugs, pirate bugs and big-eyed bugs (yes, that's really their name). Many gardeners kill these natural predators by using such insecticides as Sevin and Malathion. Spraying plants when you don't really know the problem can, as in the case of spider mites, actually worsen the problem.

Control of spider mites is made even more frustrating because few insecticides are effective, and the mites frequently develop a resistance to them rather quickly. Insecticidal soap, such as Safer, may help to some degree, although it can damage plants if used during the heat of the day. UltraFine is a highly refined petroleum oil spray that will kill mites and their eggs, but it must be used with care. Application must be repeated because of the high reproductive rate of mites, and it must be applied early in the day before temperatures reach 85 degrees. Rose Defense Spray contains neem oil, which helps smother the mites. Introducing more natural enemies, purchased from a natural-controls store, is a good idea.

Meanwhile, keep your plants well-watered, and practice your cooler-weather-and-some-rain dance, as this pest will diminish greatly with cooler weather.

Coming Up: On Thursday, Aug. 6, Lillian Maksymowicz will teach a class on Wildflowers in the Home Garden at the Southern Oregon Research and Extension Center, 569 Hanley Road, Central Point. The class is from 7 to 9 p.m. Cost is $5. Call 776-7371 for more information.

Carol Oneal is a past president of the OSU Jackson County Master Gardeners Association. E-mail her at

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