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.