I live in northern Michigan. I started removing a clump of trees that were ugly and looked like they were dying. As I started cutting each small tru...
white stuff growing on trees #851181
Asked September 25, 2023, 2:03 PM EDT
I live in northern Michigan. I started removing a clump of trees that were ugly and looked like they were dying. As I started cutting each small trunk, I observed a white styrofoam-looking something growing on the bark of most of them. There were also a few white spots on the underside of some leaves. Can you tell me what this is? Will it spread to my healthy trees? Is there something I need to do?
Based on what I see in your images:
Woolly aphids are aphids that produce a covering of fluffy white wax. One of the most common species found in landscapes is the woolly apple aphid. It is most commonly found on crabapple feeding at the base of new shoots. It prefers to suck the sap from roots, branches and twigs of apple, but may also be found on alder, elm, mountain ash, hawthorn, serviceberry, and Pyracantha. Examine trees for bluish-black aphids covered with fluffy white wax on exposed roots, wounds on trunks and branches, and at the bases of new shoots on branches. Other species of woolly aphids include the woolly elm aphid (elm, service berry as alternate host), woolly elm bark aphid (American and slippery elm), beech blight aphid (beech), and woolly alder aphid (alder and silver maple). The white material are secretions from woolly aphids. The aphids will make the leaves sticky and potentially form sooty mildew. Natural enemies in the area will usually feed on some of the aphids. This issue is not related to air circulation. There have been a number of reports of woolly aphids on beech, and we happen to be in a year where aphid populations are higher.
Neem or insecticidal soap are two chemical options. However, it would be tough to get good coverage on your tree. While the leaves may appear a bit unsightly, no chemical treatment is necessary as the tree will survive.
As for the white spots on the leaves, it’s possible that they are caused by a different issue. Without further information, it’s challenging to pinpoint the exact cause. However, some common causes of white spots on leaves include fungal infections like powdery mildew.
This work is supported in part by New Technologies for Ag Extension grant no. 2020-41595-30123 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.