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Science-based gardening information for Colorado communities from CSU Extension, Denver Botanic Gardens, and Green Industries of Colorado.

1400-11 – Kermes Scale on Oak trees   arrow

Kermes scale is a serious insect pest of pin and red oak. kermes scale

What is kermes?

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.

How can I control kermes?

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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