How Can I Control Spider Mites?

Do you want to utilize biological control?

Do you want to utilize cultural control?

Do you want to utilize low-risk chemical control?

Do you want to control spider mites with insecticidal soaps and oils?

Spider mites have many natural enemies, which limit their numbers in many landscapes and gardens, especially when undisturbed by pesticide sprays. Some of the most important are the predatory mites, six-spotted thrips, and spider mite destroyer lady beetle. Various general predators like minute pirate bugs, big-eyed bugs, and lace­wing larva will also control spider mite populations. If you wish to establish predators in a heavily infested orchard or garden that has few predators, use a soap spray or selective miticide to bring pest mites to a lower level and then release predatory mites. A good guideline is that one predator is needed for every 10 spider mites to provide control.

Cultural practices can have a significant impact on spider mites. Dusty conditions often lead to mite outbreaks. Apply water to pathways and other dusty areas at regular intervals. Water-stressed trees and plants are less tolerant of spider mite damage. Be sure to provide adequate irrigation. Mid­season washing of trees and vines with water to remove dust may help prevent serious late-season mite infestations. In gardens and on small fruit trees, regular, forceful spraying of plants with water often will reduce spider mite numbers adequately. Be sure to get good coverage, especially on the undersides of leaves.

If treatment for mites is necessary, use selective materials, preferably insecticidal soap or insecticidal oil. Both petroleum-based horticultural oils and plant-based oils such as neem, canola, or cottonseed oils are acceptable. There are also several plant extracts formulated as acaricides that exert an effect on spider mites. These include garlic extract, clove oil, mint oils, rosemary oil, cinnamon oil, and others. Don’t use soaps or oils on water-stressed plants or when temperatures exceed 90°F.

Sulfur sprays can be used on some vegetables, fruit trees, and ornamentals. This product will burn cucurbits and other plants in some cases. Don’t use sulfur unless it is safe for that plant in your locality. Use liquid products such as sulfur and potash soap combinations rather than sulfur dust, which drift easily and can be breathed in. Don’t use sulfur if temperatures exceed 90°F, and don’t apply sulfur within 30 days of an oil spray.

Certain insecticides stimulate mite reproduction. For example, spider mites exposed to carbaryl in the laboratory have been shown to reproduce faster than untreated populations. Carbaryl, some organophosphates, and some pyrethroids also favor spider mites by increasing the level of nitrogen in leaves. Insecticides applied during hot weather usually appear to have the greatest effect, causing dramatic spider mite outbreaks within a few days.