Leaf Curl in Plum Trees

There are a number of reasons for plum leaves to curl. One of them is simply dehydration, and can easily be addressed by frequent, deep watering. But when plum eaves are turning color, curling or dropping in spring or summer, it can be a sign of a serious problem. The University of Virginia at Kearneysville lists many diseases of plum trees that affect its leaves, blossoms, roots and bark. Only a few of these viruses, fungi and insects cause plum leaf curl.

Unroll a curled plum leaf with your fingers. If you see tiny, greenish-yellow, soft-bodied insects, you've got plum leaf curling aphid. Aphids eat the leaf margins, causing them to curl up and eventually drop. They don't stop fruit production, but can eventually damage the vitality of the tree if the infestation is large. Washington State University recommends controlling plum leaf curl aphid with a strong stream of water, rather than chemical applications that also kill beneficial insects.

Look for a grayish-black, slimy film on curling plum leaves, especially on the leaf margins. This fungus is called sooty mold, and it feeds on sticky excretions, or "honeydew" secreted by aphids. Sooty mold won't invade the leaf tissue, but will block some light from its surface. Sooty mold can easily be controlled if aphid populations are addressed with hard spraying with water or insecticidal soaps.

Look for early, smaller fruit among your plum tree's curling and yellowing leaves. If these symptoms occur in late summer, it's the tomato ringspot virus, which also attacks peach, apricot and cherry trees. According to West Virginia University, the virus attacks when the tree has been partially girdled, and enters through wounded trunk bark. Tomato ringspot is communicated from broadleaf weeds like dandelion, and from other infected trees. It usually defoliates and kills the tree within a few years.