Symptoms and damage
Various kinds of scale are pests of oak. Scales are unusual
insects in appearance. As adults, they are small and immobile, with no visible
legs. They vary in appearance depending on age, sex and species. Scales feed on
sap by piercing the leaf or stem with their mouthparts and sucking. As they
feed on plant sap, some scale insects (soft scale) excrete a sugary substance
called honeydew. The sooty mold fungus feeds on the honeydew, resulting in
unsightly, dark fungal growth.
Scales are not easily controlled with chemical insecticides. The
adults are protected by their waxy covering. For heavy infestations of scale
insects, spray with horticultural oil in the spring and fall to kill adults,
crawlers and eggs by smothering them. Be sure to thoroughly coat the trunk and
all of the branches.
Crawlers are susceptible to conventional insecticides, however. Monitor the
crawler emergence with sticky cards, double-faced tape wrapped around a branch,
or by putting an infested shoot or leaf into a baggie and watching for crawler
movement. Insecticides labeled for use by homeowners against scale crawlers on
oaks include cyfluthrin, permethrin, bifenthrin, lambda cyhalothrin, malathion,
and carbaryl. Apply one of these materials when crawlers appear and repeat in
10 days. As with all pesticides.
Share this article