Red maple tip damaged by maple shoot borer. Photo: SD Frank
Maple shoot borers (Proteoteras aesculana) are common pests of red maples in nurseries. Amanda Taylor, Area Specialized Agent – Nursery and Greenhouse, just emailed an alert indicating maple shoot borers are active in WNC nurseries now. Maple shoot borers are caterpillars that bore into young maple tips. They cause flagging and dieback of the apical shoots.
Maple shoot borer adults are small nondescript moths that lay eggs on maple stems near expanding buds in early spring. After hatching the caterpillar burrows into the growing shoot where it feeds on the vascular cambium. As the larvae develops it expels frass and silk from the hole through which it entered the stem. Young stems and leaves above the point where the larvae entered eventually die. Mature larvae exit the shoot then pupate on the ground.
Red maple tip damaged by maple shoot borer. Photo: SD Frank
Monitoring for damage by this pest is not very useful because by the time damage occurs management is impractical. However, if a high proportion of plants are infested this year it could warrant preventive insecticide applications next spring. To confirm that damage is from maple shoot borers and not another pest like potato leafhoppers, cut open flagging stems to see if they are hollow and if larvae are present. The larvae are a tan to cream-colored with a dark head capsule.
Dissected maple stem showing larvae living inside. Photo: SD Frank
Preventive management entails applying pyrethroid insecticide from just before bud break until shoots have flushed their first two pairs of lateral leaves. Since this is in early spring you may be making these applications anyway for ambrosia beetle management so there is no need to spray extra just for maple shoot borer. Preventive applications are important because once symptoms appear it is too late for treatment. Damaged shoots should be pruned and a new leader trained to correct tree form.