Oak trees dropping clumps of leaves with twigs

Asked September 25, 2019, 1:06 PM EDT

Could the tree have bugs or a disease?

Ramsey County Minnesota tree losing leaves anthracnose oak wilt

7 Responses

Thanks for the question.

If the oak branches that are falling have green leaves on them, you are most likely seeing the result of squirrel nest building activity. Normally this is more common in early summer and/or early winter. That it might be occurring now is a bit unexpected. However this year has also seen spring shrubs (e.g., lilacs) blooming a second time. Perhaps squirrels are also exhibiting some unexpected nesting impulses. See:

https://www.dnr.state.mn.us/mammals/graysquirrel.html

https://animals.mom.me/nesting-habits-gray-squirrels-3948.html

If squirrels are doing this, there will be no harm to the tree. If you look up towards the top of your oak trees, you may even see these nests. Look at:

https://www.perkypet.com/articles/squirrel-nests

Please let us know if you have any additional questions!!

Unfortunately it’s clumps of dead leaves with a twig attached to each clump. Each twig looks like it’s been cut off. It appears to be spreading on the tree.

Thanks for the response.

Before posing other possibilities to you, it will be important to determine if these twigs are alive or dead. Could you please do one more thing?. Take a few twigs that have recently fallen and with you finger nail or a knife, gently scrape off some of the bark. Look at the color of the plant tissue beneath the bark. If it is whitish-green, the twig is alive. If it is brown or darker, the twig is dead.

If it is some type of disease, oak wilt (caused by a fungus) is the most likely possibility. It is rather common in Minnesota, especially among red oaks. Here is a site to look at and compare the symptoms of oak wilt with what you see on your oaks:

https://extension.umn.edu/plant-diseases/oak-wilt-minnesota#symptoms-of-oak-wilt-1258960

Many thanks!!

Thanks for getting back to me so quickly. I read the information you sent but still not sure. I’m attaching some pictures I just took. Hope that helps. Thanks! Dawn

Hi Dawn,

Thanks for getting back to us.

I am now leaning away from thinking squirrels might be the culprit. The left picture of what you sent shows both brown and green areas on the leaves. This is typical of a fungal disease of oaks called Anthracnose. It looks as if you have a white oak. Anthracnose is more common in white oak than in red oak. This infection can start in the spring under cool, moist conditions. I suspect that this might have been the case for your property last spring. This disease begins on lower regions of the tree and progresses upward. If this is the case, normally it is not a serious threat to the tree. With time, the Anthracnose infection can spread from leaves to twigs. This in turn can cause twigs to drop. Spores of this fungus can remain in leaf debris over the winter. For this reason be sure to remove all fallen leaves and twigs from under your oak this fall, place them in a leaf bag, and dispose of accordingly. Do not compost them. One proactive measure might entail fungicide spraying early next spring. Here are some publications dealing with Anthracnose:

https://www.extension.iastate.edu/news/2006/jul/070301.htm

https://ag.umass.edu/landscape/fact-sheets/oak-anthracnose

https://extension.umn.edu/plant-diseases/anthracnose-trees-and-shrubs

Another common fungal oak disease is called Oak Wilt. It tends to be more common in red oaks than white oaks. Unlike Anthracnose, it is a serious disease and can lead to the death of the tree. However it generally begins with leaf browning at the top of the tree and progresses downward. This does not appear true for your tree. Nevertheless, here are two sites describing this disease:

https://extension.umn.edu/plant-diseases/oak-wilt-minnesota

http://www.myminnesotawoods.umn.edu/oak-wilt/

Your right picture shows an entire large branch with dead leaves on it. I suspect that this is due to the branch breaking from wind. I don’t think it is caused by any disease.

The following publication is an excellent summary of several oak diseases with pictures. In looking at it, focus upon what it says regarding Anthracnose and Oak Wilt:

https://www.fs.usda.gov/naspf/sites/default/files/publications/9190_fh_howtorecoakdis_508.pdf

Bottom line: It would appear that your oak might have Anthracnose. However other possibilities, including Oak Wilt, cannot be ruled out. For a definitive answer on this, I would strongly suggest that you have a certified, professional arborist make an on-site inspection and evaluation of your oak this fall. Here is a University of Minnesota publication describing the selecting of such an individual:

https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

Finally, take a look at:

https://www.primebuyersreport.org/industry/ramsey-county-mn/st-paul/tree-service/

Please get back to us if you have any further questions. We will be glad to try and answer them.

Good Luck!!

Thank you so much for all of your time and information, Steve. It was very helpful. I really appreciate it!!

Hi Dawn,

Glad to help you. Good luck with your oak.

Thanks for using this forum!!