Last summer, I noticed the telltale signs of mites on my eggplant and squash. Can mites be eradicated using non-pesticidal means? If not, what are the best anti-mite products available?
Steve Davis, Jackson
According to UC Master Gardener Carol Rogala, mites are common pests in landscapes and gardens that feed on many fruit trees, vines, berries, vegetables and ornamental plants.
Although related to insects, mites are members of the arachnid class along with spiders and ticks. Spider mites, also called web-spinning mites, are the most common mite pests.
For identification, spider mites look like tiny, moving dots to the naked eye. A small number of mites usually isn't reason for concern, but very high populations can damage leaves.
On annual vegetable crops such as squash, melons and watermelons, the loss of leaves can have a significant effect on yield and lead to sunburning.
Spider mites have many natural enemies that often limit populations. Adequate irrigation is important, because water-stressed plants are most likely to be damaged.
Broad-spectrum insecticide treatments for other pests frequently encourage mite outbreaks by killing beneficial insects that prey on mites, so avoid these pesticides when possible.
In gardens, regular, forceful spraying of plants with water often will reduce spider mite numbers adequately. Be sure to get good coverage, including the undersides of leaves.
If more control is required, use an insecticidal soap or horticultural oil in your spray, but test the product on one or two plants to be sure it isn't damaging to them.
Both petroleum-based horticultural oils and plant-based oils such as neem, canola or cottonseed oils are acceptable.
A number of plant extracts formulated as acaricides (a pesticide that kills mites) exert an effect on spider mites. These include garlic extract, clove oil, mint oils, rosemary oil, cinnamon oil and others.
Oils and soaps must contact mites to kill them, so excellent coverage, especially on the undersides of leaves, is essential, and repeat applications may be required.
Sulfur sprays can be used on some vegetables, fruit trees and ornamentals. This product will burn cucurbits (squash, cucumber, melon) and other plants in some cases. Don't use sulfur unless it has been shown to be safe for that plant in your locality.
Most important, if you decide to use a chemical control, read and follow the directions carefully.
A complete description of this pest's identification, life cycle, damage, and management can be found online at www.ipm.ucdavis.edu.
Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.
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