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?

Cheboygan County Michigan

Expert Response


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.


Beech Blight Aphids are Jitterbugging Across Ohio at this link:

Woolly Aphids on Trees - University of Maryland Extension:

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.

Powderly Mildew - IPM - MSU at this link:

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I hope this helps!
Melville Kennedy Replied September 25, 2023, 3:58 PM EDT
Thank you for your quick, thorough response.  That is very helpful.
On Mon, Sep 25, 2023 at 3:58 PM Ask Extension <<personal data hidden>> wrote:
The Question Asker Replied November 02, 2023, 1:23 PM EDT
You are welcome! Have a great day!
Melville Kennedy Replied November 02, 2023, 2:40 PM EDT

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