Calls are starting to float around the region regarding Walnut Caterpillars. These guys can defoliate a tree in fairly short order.
In the case of Walnut Caterpillars early identification and control is the best option to prevent significant defoliation. The upside is that trees or branches which are defoliated will regrow.
Additional information on identifying and combating these caterpillars can be found in the Walnut Caterpillar Flyer (ENTO-041).