Spruce Spider Mites Of Leyland Cypress

Disease Information

Spruce Spider Mites

Symptoms and damage

 Mites are not insects but are more closely related to spiders. Spruce spider mites (Oligonychusununguis) are occasional pests of Leyland cypress. They are very small and not seen easily with the naked eye. They have piercing mouthparts that they use to suck plant sap. Their feeding results in speckling (formation of tiny yellow spots) on needles. Some needles may turn brown and drop off. With heavy infestations, fine webbing may be seen on the plant. Several seasons of heavy mite feeding may kill a Leyland cypress. Although most spider mites increase in number during hot, dry weather, spruce spider mites are cool-weather mites. Their population peaks during spring and fall, but drops dramatically during the heat of summer when predators feed upon them.


 Naturally occurring enemies of mites include various predator mites, lady beetles (ladybugs) and other insects. These predators will usually suppress mite populations. Since insecticide use kills beneficial predators as well as mites, insecticides should be avoided unless absolutely necessary. Overuse of insecticides can result in population explosions of mites by their natural predators. However, insecticidal soap and horticultural oil sprays are less harmful to beneficial insects. Mites can be removed with a strong spray of water, when applied on a regular basis as needed.

To determine whether miticide use is needed, it helps to know how many mites are present. Hold a white sheet of paper under a branch and tap the branch with a pen. The mites that are knocked off will be seen crawling around on the paper. If dozens of mites are seen per tap, serious damage can result. Continue to check population numbers at 7- to 10-day intervals. Populations will be greatest during the spring and fall.

Pesticides labeled for homeowner use against spruce spider mites include insecticidal soap, horticultural oil, neem oil, tau-fluvalinate, lambda-cyhalothrin, and malathion.


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