Spider mites feast on ornamentals in Kansas
A common year-to-year problem with ornamentals in Kansas is spider mites. They can be a problem on spruce trees especially, but the problem with spider mites is not just the damage they cause, but also the lack of methods to control them. Before you can control them, you need to know if you have them. The damage they do can be subtle at times, so taking a second look is often required.
Spider mites have mouthparts that are designed to pierce individual plant cells and remove the cell contents. Their feeding over an area will cause the plant to have tiny white or yellow colored speckles on the leaves. The whole leaf can begin to look yellow or bronzed if heavily infested. The bronzed foliage can drop prematurely, and in the worst scenario, the plant can die from a heavy, untreated infestation. There are certain "web" producing types of spider mites, so another sign to look for is a fine, silky covering on the infested foliage that gives it a "dirty" appearance when the web attracts dust and dirt.
Unfortunately, most of the chemicals used against spider mites are only available to commercial applicators. The active ingredient, bifenthrin, is commonly used by commercial applicators but is now available to homeowners under the name "Ortho's Rose and Flower Insect Killer."
This Ortho product is not for use on edible crops, but provides a formidable defense against spider mites on ornamental plants. Another miticide available to homeowners is the chemical lambda cyhalothrin. It is sold under the name "Spectracide Triazicide" and is labeled for use on many ornamentals as well as some members of the brassica family (cabbage, broccoli, cauliflower and kale).
One of the problems with using a miticide is that it, like many chemicals, kills the beneficial mites as well as the harmful ones. Potentially there are many predatory mites feeding on the harmful ones, and they also will be killed by a chemical application. Be sure you have a problematic spider mite infestation before you spray chemicals.
If using a conventional miticide is not what you wish to do, a horticultural oil can be a useful tool against spider mites. Horticultural soaps and oils are a good alternative to conventional pesticides and can be quite effective, especially when the infestation is low to moderate. These soaps and oils are also kinder to the predatory or beneficial mites that also inhabit the plant. When using the oils, be sure to spray the top and bottom sides of the leaves for best control of all three life stages of the mites (eggs, immature, and adult). If you have any questions about spider mite control or have any other agriculture or horticulture questions, feel free to contact me at the Leavenworth County Extension Office on the corner of Hughes and Eisenhower roads in Leavenworth, or call (913) 250-2300. I can also be reached via e-mail at firstname.lastname@example.org.