Leaf drop pin oaks
I have 2 40 year old pin oaks that have started to drop their leaves. The leaves are still green, but on the underside of each one there are small tan discolorations at the junctions of the veins. On a tree I plucked off the tree, there is a fuzzy tan colored multilegged insect about 5 mm long.
My apology for not responding sooner. It got lost in my holiday week activities. Early leaf drop can be caused by a number of things, such as drought stress, spring frost damage, lightning strikes, or diseases such as bacterial leaf scorch, oak wilt, anthracnose, and insect damage. The following link will provide more insight into the above diseases: http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/oak-diseases Based on your observations and comments it might be oak leaf blister although that does not ordinarily result in leaf drop. You might compare the pictures on this web site with your situation. It might possibly be anthracnose. You could also feel free to respond with one or two pictures that might help to better indemnify the cause. Orange stripped oak worms also attack pin oaks but your description doesn't seem consistent. It might the variable oak leaf caterpillar but a picture might better aid in identification. If you have the time you could take a sample of the fallen leaves and the caterpillar to your local Penn State extension office. If time doesn't permit then pictures attached to your response might be best. Hope this is helpful. Thank you.