It has been hot and dry, a combination that favors the development and rapid reproduction of the spider mite according to Kelly McGowan, horticulture educator, University of Missouri Extension.
"These mites are capable of infesting many garden, tree, shrub and bedding plants. Beans, melons and tomatoes are only a few susceptible vegetable garden crops," said McGowan.
Annual flowers — such as marigolds and petunias — are quite vulnerable. Common landscape plants affected by mites include azalea, cotoneaster, Alberta spruce and roses.
Mites damage plants by sucking contents from leaf tissue. The initial damage appears as a stippling of light dots on the leaves. As feeding continues, the leaves turn yellow or bronze in color and drop off.
Because spider mites are very small, they can be difficult to see on plants.
"Check for spider mites by holding a piece of white paper underneath a branch and shake or tap the branch sharply. If mites are present, some will be dislodged from the leaves and fall onto the paper where they will be seen as tiny moving specks," said McGowan.
Predator insects often take care of spider mite populations. But, if pesticide treatments are needed, confine the applications to those plants most seriously infested to help conserve the natural enemies.
"Spider mites flourish on plants under stress. Keeping plants well watered and fertilized can help to minimize the stress," said McGowan.
Mite populations can also be reduced by forcefully spraying plants with water, especially on the undersides of leaves, to break up the webs and wash the mites off.
Insecticides such as Kelthane (dicofol), malathion or insecticidal soaps are common mite controls with vegetable crops. Acephate (Orthene) works with bedding plants, trees and shrubs. Coverage on the undersides of the leaves is essential and repeated applications may be necessary.
For more information, contact one of MU Extension's horticulture specialists or educators in southwest Missouri: Patrick Byers in Webster County at (417) 859-2044, Kelly McGowan in Greene County at (417) 881-8909 or Robert Balek in Jasper County at (417) 358-2158. Or, call the gardening hotline operated by the Master Gardeners of Greene County at 417-874-2963.