Kermes Scale on Oak trees
Kermes scale is a serious insect pest of pin and red oak.
The symptoms of Kermes scale infestation include brown leaves, brown branch tips, and twig dieback. Gummy ooze forms outside of the adult scale insect and also will appear on the brown branch tips. The bacterial ooze is known as “drippy blight of oak” and is found in association with kermes infestations. Yellowjackets may be attracted to and feed on the bacterial ooze.
Kermes overwinters as an obscure nymph on the branches of the oak tree and concentrated around leaf buds. In the spring, the nymphs become immobile, feed on tree sap, and mature into an adult. The adult female scales are tan to brown, 1/4” in diameter, round and immobile. The scale resembles a small marble. In the late summer, the adult female lays eggs and dies. The eggs hatch in September and October migrating to their overwintering sites.
There are 3 common ways to control kermes scale. The scale may be controlled with a spring dormant oil spray application completed before the oak trees leaf out. This will smother the insects before they can turn into an adult. Fall time sprays with a pyrethroid insecticide including active ingredients permethrin, lambda-cyhalothrin, or bifenthrin may be applied. This will control kermes when the scale crawlers are migrating. Finally, soil applications with insecticides containing the active ingredient imidacloprid may also be applied. The insecticide is taken up systemically by the tree roots and into the tree canopy controlling the scale. It may take up to a year following the application before the soil applied insecticides control the kermes scale.
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Updated Monday, January 09, 2017