Identification and Life Cycle of Scale Insects
Scale insects are a common pest on a wide variety of trees, shrubs, and fruit trees. There are many species of scale found in Oklahoma, including brown elm scale, euonymus scale, crapemyrtle bark scale, armored scale, etc. Look at twigs and branches for small (3mm or smaller) round to oval gray/brown raises on the bark of trees. Crapemyrtle and Euonymus scale will be white. The scale waxy cover protects the insect and eggs underneath. A black or gray crust may form on the twigs, branches, or trunk. Heavy scale infestations kill small branches, stunt tree growth, and devitalize the tree until it is subject to attacks of borers and diseases.
Scales overwinter and mature in the spring. Eggs are laid beneath the female’s body in late April and early May and hatch into tiny lice-like nymphs in early and mid-May. The young, called crawlers, come out from beneath the scale covering and migrate to the leaves and small limbs. In autumn, the scales migrate to the bark of the smaller branches, where they spend the winter.
Control of Scale Insects
Scale is difficult to control without the use of systemic insecticides, which are used to control most sucking pests. Be aware of the risk systems pose to pollinating insects such as honeybees and bumble bees, and do not apply while the plants are in bloom.
Bio Advanced 12 Month Tree & Shrub – Protect & Feed provides 12 months of systemic protection against damaging scale insects. Apply granules around the base of the trunk and water into the soil. Determine the rate based on the trunk diameter or height of the shrub. BEE CAUTION: Do not apply to plants in bloom.
Most non-systemic contact insecticides cannot penetrate the protective, waxy layer of scales. Thus, sprays should be applied to target the crawler (nymph) stage. Carefully read the labels of insecticidal products for phototoxicity statements.
- Bonide Malathion Insect Control
- Garden Tech Sevin Insect Killer
- Natria Insecticidal Soap
- Bonide Neem Oil
- HiYield Dormant Oil Spray (apply in winter only on deciduous plants)
