Fruits Affected

Apple, Plum, Cherry, Apricot

Also See

The American plum borer is the caterpillar of a grey-brown moth (Euzophera semifuneralis) with brown-red forewings. It infests plum, cherry, apricot, and apple trees, entering trees through wounds created by machinery, extreme weather, and disease.

Symptoms

Visible holes or damaged areas in tree bark that ooze gum.

Organic Treatments

The most obvious way to avoid APB is to keep your trees otherwise healthy and protect them from unnecessary damage. Your risk of DPB can be minimized by staying away from rootstocks that are especially prone to burr knots: the Malling and the Malling-Merton series and B.9. Painting the lower trunk with latex paint can also reduce chances of DPB infestation, as can protecting the rootstock with piled up soil or burlap.

Conventional Treatments

A course spray onto the burr knots with Asana.

Insect Cycle

The American plum borer is the caterpillar of a grey-brown moth (Euzophera semifuneralis) with brown-red forewings. It infests plum, cherry, apricot, and apple trees, entering trees through wounds created by machinery, extreme weather, and disease. Similarly, the dogwood borer is the caterpillar of a small clearwing moth (Synanthedon scitula) that infests apple trees, especially those grown on particular rootstocks. Like peach tree borers, the adult moth of the DWB resembles a wasp with its abdomen showing distinct black and yellow bands.

The larvae of both moths hibernate over winter under the bark of the tree and become active in the spring. After emerging, adults begin to breed immediately. The APB lays its eggs on or near existing wounds, while the DWB favors burr knots (tumor-like clusters of root initials found on the portion of the rootstock that is above ground). The larvae feed on the cambium (inner bark) of the tree, which is essential to the tree's health and vigor. A heavy infestation of borers can weaken or kill a tree outright. To identify borer, inspect your trees for damaged and dark areas on the bark that are oozing gum. A powdery frass (excrement) will often be visible around a borer hole. You should be able to peel back the bark and find the active larva itself if it still in the tree.

For more information, see the Cornell IPM Factsheet on American Plum Borer and the IPM Factsheet on Dogwood Borer. (The latter publication is somewhat dated, as we now have available the Geneva series of rootstocks, most of which do not produce burr knots.) For a discussion of organic practices, see Cornell's A Grower's Guide to Organic Apples.