Key Features
- Bronzing of leaves or needles
- Webbing on underside of leaves
- Spider mites and eggs on leaves
Symptoms
Spider mites feed on plant leaves by piercing leaf tissues and sucking the green liquid that oozes out. Leaves appear bronzed after the green color is lost from many tiny feeding spots. Heavy infestations can defoliate trees and cover leaves with fine webbing. The best way to confirm a spider mite infestation is to hold a sheet of white paper under a branch and then tap the branch sharply. If present, they will fall off and be seen as tiny specks crawling over the paper. The ability to crawl clearly distinguishes mites from the grit that can be knocked off a plant. Leaves infested with spider mites will usually have fine webbing and eggs on the leaf undersides. Although spider mite injury is superficially similar to that of lacebugs, spider mite injury can be distinguished by the presence of webs, egg shells on the mid-vein, and lack of tar spots on the leaf surface.
Biology
Spider mites are tiny, 8-legged animals that are closely related to spiders. Under favorable conditions, spider mites can build up rapidly and seriously threaten plant health. Most of the common spider mites of trees and shrubs winter on the tree. Two spotted spider mite is an exception to the rule. It winters in the leaf litter. Most species of spider mites cause the greatest damage on plants in the warm part of the summer when the maximum temperature is consistently above 85 degrees F. These include two-spotted spider mites, honeylocust spider mite, European red mite, maple spider mite, boxwood spider mite and oak red mite. A second group of spider mites are more active during the cool season when the maximum temperature is less than 85 degrees F consistently. These species include spruce spider mites and southern red mites which are pests of conifers(pine, spruce, etc.) and broadleaf evergreens respectively (azalea, rhododendron, holly).
Management Recommendations
Spider mites thrive on plants that are under water or nutrient stress. Be sure to keep plants well watered and give them adequate light. Do not over fertilize or under fertilize. Dry weather favors spider mite outbreaks because rain can knock them from leaves and promote fungal infection. If the foliage is accessible by a garden hose sprayer, light infestations can be managed by spraying the foliage with a hard stream of water twice, weekly. Many natural enemies keep spider mites from becoming pests. Avoid spider mite problems when controlling other pests by using those pesticides that do not kill the predators of spider mites. If the water stream does not control the spider mites, try insecticidal soap, horticultural oil, or neem oil. Professionals can use products that kill mites (eg bifenazate, clofentazine, hexythiazox, and spiromesefin) but spare predators.
Effective Pesticides
Active Ingredients include: Azadirachtin, Bifenazate, Horticultural oil (Paraffinic or superior oil) , Insecticidal soap (Potassium salt of fatty acid), Neem oil, Spiromesefin
