Oaks can be stripped of their leaves practically overnight by May beetles. Active now, these beetles are approximately 1" long and cylindrical, color varies from brown to black.
The species which attack oak feed at night, stripping the foliage and leaving only veins. Consequently, the damage is present but there is no sign of the cause. The beetles leave the trees during the day and may be found under leaves or grass around the tree. Sevin is very effective against these insects. The feeding period lasts for several days but one treatment should be sufficient.
The larval stages are white grubs that feed on the roots of grasses. Large expanses of turf or pasture can produce thousands of these beetles. Fortunately, the beetles are around for only a short time and oaks will push out a new set of leaves.