What is causing this black pitch to drop from our maples?

Asked September 5, 2015, 7:55 PM EDT

All of our maple trees have been dropping a black substance that is over everything. It has never been like this before. It coats cars, boats, driveways, roofs, and decks. It seemed to start last summer, but this summer it is almost unbearable. What is it and what can we do to control it? We live along Torch Lake in Antrim County.

Antrim County Michigan maple trees

3 Responses

It sounds like your trees have been attacked by sucking insects which produce a honeydew which in turn grows a sooty mold. Sooty mold is a fungus which grows on the honeydew. As the name implies, it is sooty in color and the honeydew can be produced so heavily that it drops from the leaves to objects below the trees, where the fungus can grow and look like pitch.

Control of the insects would be necessary to prevent sooty mold. Control of sooty mold is targeted at preventing or reducing insect populations. Scales and aphids are usually the culprits in sooty mold infestations. It's important to identify the species of insect present by checking your trees and see if you see aphids or scale. After finding which insect is doing the damage, you can then determine what control measures to apply and when. Check your trees and see if you see aphids or scale.

The following sites have more information on both aphids and scales:

http://www.na.fs.fed.us/spfo/pubs/howtos/ht_sooty/ht_sooty.htm

http://learningstore.uwex.edu/assets/pdfs/A3123.pdf

http://msue.anr.msu.edu/news/using_horticultural_oils_on_landscape_plants

I hope this was helpful. Feel free to contact us if you have further questions.

We live in an area where there are hundreds of mature maples and the problem is widespread. Is there any hope that this problem is not long-term?

Not knowing for sure what insect is causing this, I can only tell you that usually weather and natural enemies of these insects will keep the population under control. Most are eaten or attacked by a complex of natural enemies, especially lady beetles. Having many trees would be cost prohibitive to treat chemically. Some years the insect population increases above normal, perhaps every 1 or 2 years, but should die down after that.

Good luck. Feel free to contact me again if you have further questions.