Try a night inspection if there's nothing visible during the day. If still nothing, then whatever pest did it has moved on.

Oaks are well able to cope with lots of holes eaten in their leaves, you shouldn't need to do anything about it.

Resin

Can you post a pic? What the damage looks like could narrow down the culprit.

Gypsy moth populations seem to be rising in several places, maybe that is what caused the damage.

I agree with Resin, oaks and all trees tolerate some degree of leaf damage. Trees can also survive complete defoliation when there is an insect epidemic.

If your tree is still a sapling, keep a close eye on it next year and pick off any caterpillars or sawfly larva. If it is a mature tree, it's less of a worry.

Here are two photos - one is a mild example and one is an extreme example. The majority of the damage is somewhere between.

http://i306.photobucket.com/albums/nn245/ixodid/oak_leaf_one.jpg
http://i306.photobucket.com/albums/nn245/ixodid/oak_leaf_two.jpg

Any guesses as to what it is?

How to prevent it next year?

Is there a way to post photos directly to this forum?

Thank you!

Tried to look at your pics - photobucket says they have been removed.

There is a way to post pics direct - but I am not tech savvy and can't advise.

This link should work:

http://s306.photobucket.com/albums/nn245/ixodid/examples/

Here is a link that might be useful: oak leaves

That damage was likely caused by gypsy moth. The young larva make the small holes, and as they grow they make larger holes and eventually consume the whole leaf.

Go to the link below and look for "Gypsy Moth Guide for Homeowners" and te pdf file will give you tips on dealing with them.

Here is a link that might be useful: City of Toronto gypsy moth web page

Geesh, they look like Swiss Cheese. My county in Ohio is under Gypsy moth quarantine, but South West Ohio is not, to the best of my knowledge. I agree it does look like the type of damage typical of them, but I don't think they are to SW Ohio yet. You might want to call your local ag extension agent. If it is G.M. he/she would want to know. If it isn't, I think they could prolly tell you what has been hitting oaks in your county. When did you first notice the damage?

Here is a link to a better photo:

http://s306.photobucket.com/albums/nn245/ixodid/examples/?action=view&current=oakleaves.jpg

Just as a follow-up, here is what I found out:

It is the damage done by the oak leaf shothole leafminer. This small fly makes a series of feeding punctures in the leaves while they are very small, then the female will lay an egg and the larva will make a little blotch mine at
the tip. The mine damage often drops off as the leaf expands and the holes get larger. No control is recommended as the health of the oak trees does not seem to be affected. I would suspect that one of the neonicotinoids (Merit, Arena, or Safari) would eliminate this little fly if applied (by soil drench or injection) before bud break of the oaks.

David Shetlar (the BugDoc)
The Ohio State University, Department of Entomology
1991 Kenny Road
Columbus, OH 43210
Office: 614-292-3762
FAX: 614-292-9783

Here is a link that might be useful:

I live in Bethany Beach, DE, and find all types of oaks in my area have these swiss cheese holes. Also looks like these trees tend to produce copious amounts of leaves. Looks like this is to insure tree will be able to photosynthesize as more leaves become infected. Have seen this in oaks as far away as Baltimore. Hard to imagine that trees so infected can continue to live since te fly that causes damage can live on hiding in bark during winter months to do their damage in spring. A new park here planted small oaks and they probably will die since all leaves are affected and branches now are dead. Also, bark on these smaller trees is loose and cracked.