We have several oak trees in front of our hosue and I just noticed yesterday that one of the smaller ones is all of a sudden dropping clumps of leaves still attached to branches. There appear to be some small brown spots on the leaves but what is much more alarming is that around the branches are cocoon-like encasements that are very hard and about 1" in diameter. These appear to be choking off the branches causing them to drop. Any idea what this might be and how do we get rid of it? How do we prevent it from spreading to the other trees. Is an arborist the correct person to call for this? I'm very concerned that this is going to kill off all the trees in front of our house.
I greatly appreciate the help
Glen Frick
Voorhees, New Jersey

Here's a little more info. I got down a couple of branches to look closely at the cocoon-like things and it turns out that they are made of solid wood and appear to be part of the branches themselves-they kind of look like tumors. It looks like they have very tiny pin-like holes or channels but I could not see anything live coming or going out of those holes. I haven't seen this on the other trees next to it.
Any help would be hugely appreciated.

Glen, it is always risky to try to diagnose something like this without seeing it. But, I’ll try anyyway.

From your description it sounds like either gouty oak gall or horned oak gall. The only real difference in appearance is that there are small protuberances or horns sticking out of the second one. These galls are caused by tiny wasps (non-stinging). The eggs are laid in the twigs, and the larvae secrete enzymes that cause the wood to form the gall. So your observation that it looks like part of the twig is accurate.

There is little that can be done for this. Susceptibility is dependant on several factors, and some years are worse than others. Pesticide treatments often do not yield very good results, as timing is critical and the insect is a tough little critter.

The galls can cause the twigs to break off, especially in high winds (we’ve had our share recently in the Philadelphia region).

Another possibility is that the galls are present, but squirrels may be clipping the leaf clusters to make nests. They often bite off the ends of twigs with leaves. Look closely at the base. It will be cleanly cut at a sharp angle, maybe leaving a little long bark hanging on the end. You may even see a ridge running down the middle of the cut surface.

The trees should be OK and will probably recover if they are not significantly stressed. Pruning to remove many of the galls might help, but it is likely that the insects have already emerged.

--Penn State Extension- Oak galls

Contact the Cooperative Extension at Rutgers for more information, or find a local certified arborist- ISA Certified Arborists.

Thanks Russ. That is exactly what it appears to be from the pictures in the link. I tried to upload a couple of pictures but had some trouble. I'm partly comforted in knowing that it is not likely 'terminal' but I am concerned about it spreading to the other trees with subsequent seasons. I'll find a local arborist to consult for treatment options. Any suggestions in the Voorhees/Cherry Hill area?
Thanks again
Glen