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Massive tiny undeveloped acorns falling from black oaks from trees throughout my area. Why? #768076

Asked August 19, 2021, 7:11 AM EDT

In the past few days what appears to be tiny undeveloped acorns, see image, have been falling like raindrops from the large black oaks in my yard and neighbors all around. Why? We are in oakland county. Lived here over 20 years and have never seen this. Trees appear healthy although we have had some oak wilt in the neighborhood. We have many large oaks in the area. Thank you.

Oakland County Michigan

Expert Response

Hello Dee,

Would you mind cutting several of these in half— two along the “equator” or middle, and two from top to bottom? Lay them out so we can see inside, and take one or two clear pictures.

This will help identify what might be going on. I will watch for your update. Thank you.

Thank you for your question!   Laura S.      Michigan State University Extension Advanced Master Gardener Volunteer You may also contact the toll free MSU Extension lawn and garden hotline at 1-888-678-3464 with your gardening questions or visit www.migarden.msu.edu for Smart Gardening resources. Replied August 19, 2021, 11:55 AM EDT
Thank you. Hope this helps.

-------- Original message --------
From: Ask Extension <<personal data hidden>>
Date: 8/19/21 11:55 AM (GMT-05:00)
To: Dee bovio <<personal data hidden>>
Subject: Re: Massive tiny undeveloped acorns falling from black oaks from trees throughout my area. Why? (#0038007)

The Question Asker Replied August 19, 2021, 12:38 PM EDT
I sent a previous email with 5 pics of split tiny acorns.
I also wanted to send this pic I just took of a large bee holding another smaller dead bee (wasp?). This is something I've never seen before as well. I don't know if it has anything to do with the tiny acorn drop problem...but it certainly is interesting. Is that a dead bee or wasp? Thank you.

-------- Original message --------
From: Ask Extension <<personal data hidden>>
Date: 8/19/21 11:55 AM (GMT-05:00)
To: Dee bovio <<personal data hidden>>
Subject: Re: Massive tiny undeveloped acorns falling from black oaks from trees throughout my area. Why? (#0038007)

The Question Asker Replied August 19, 2021, 1:01 PM EDT
I just did a little more scouting in the yard, looking at fallen branches. Looks like its NOT an acorn...I think it is some sort of leaf gall. Please let me know what type of gall this is and if I should be concerned.

-------- Original message --------
From: Ask Extension <<personal data hidden>>
Date: 8/19/21 11:55 AM (GMT-05:00)
To: Dee bovio <<personal data hidden>>
Subject: Re: Massive tiny undeveloped acorns falling from black oaks from trees throughout my area. Why? (#0038007)

The Question Asker Replied August 19, 2021, 1:21 PM EDT

Thank you for the clear pictures. Yes this really does help.

I believe what you have is some type of an oak gall falling from the trees which is perfectly normal this time of year. This might be bullet gall or young speckled gall. Galls do not harm trees and don’t endanger their health at all.

Here is a link to galls that describes their life cycle- https://bygl.osu.edu/node/1681

There are many other kinds of galls. When you cut the objects in half I could see that this wasn’t an acorn but was the fibrous tissue formed by a tiny wasp laying its larvae on the tree which forms the gall, with a chamber for the larva in the center. Also, these objects do not have an acorn cap, which green acorns should have.

More examples of galls—

https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/oak/branchesgrowths.html

https://bygl.osu.edu/node/1042

If you would like to get a second opinion, an perhaps an exact ID on which gall this is, please submit all your pictures to MSU Plant and Pest Diagnostics lab at <personal data hidden>


The insect holding the dead one is probably taking the insect back to its nest to feed its young. Many wasps do this. I will refer your question to our entomologist who may be able to provide more information.

Thank you for your question!   Laura S.      Michigan State University Extension Advanced Master Gardener Volunteer You may also contact the toll free MSU Extension lawn and garden hotline at 1-888-678-3464 with your gardening questions or visit www.migarden.msu.edu for Smart Gardening resources. Replied August 19, 2021, 1:21 PM EDT
Thank you! Your information is very helpful. I will share it with the neighbors.

-------- Original message --------
From: Ask Extension <<personal data hidden>>
Date: 8/19/21 1:21 PM (GMT-05:00)
To: Dee bovio <<personal data hidden>>
Subject: Re: Massive tiny undeveloped acorns falling from black oaks from trees throughout my area. Why? (#0038007)

The Question Asker Replied August 19, 2021, 2:27 PM EDT

Hello Dee,

That is "bee" is actually a bee mimic robber fly, Laphria spp. (Asilidae).

See https://bugguide.net/node/view/21334

Best regards,

Howard

Howard Russell, Entomologist Replied August 24, 2021, 10:41 AM EDT

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