One of the most difficult dry weather consequences to witness in the San Marcos ecology is the browning and leaf loss of trees. Some trees seem to have all their leaves suddenly turn brown and then drop, others seem to yellow and fall as they would normally in October or November. Are the trees dead or just drought deciduous -will they come to life next spring?
“Well that depends,” says Kelly Eby, the urban forester with the city of New Braunfels, “each species and each situation can vary quite a lot.” The drought stress causes a fungi known as hypoxylon, which is ever present on almost every healthy tree, to begin killing some species and varieties more than ohters. Spanish oaks and hackberries are particulaly vulnerable. Trees taken over by hypoxylon will have leaves turn brown rather quickly and perhaps unevenly before they fall. (as seen in photo of a red oak) The bark is the place to look to determine what is happening. The hypoxylon will create a distinct mottled look on the bark and
even eat away the bark to the woody interior of the tree. Images are available from the Texas Forest Service website noted below.
Most of the trees are accustomed to surviving dry weather so a judicious amount of water applied under the drip line of the tree may fend off severe stress. But some trees are not well suited to their site to begin with and water is in short supply. It may be better to replace some trees with a species that is better adapted to the area, and to mulch and develop the soils around the tree to preserve moisture.
What to do? Like Eby says, it depends. But she is certain of one thing, if you have a tree you are concerned about get a free consultation from a certified arborist before you take any drastic measures.
Here is a link to the Texas Forest Service website to learn more about the disease: http://txforestservice.tamu.edu/main/popup.aspx?id=1262