Question
We live in Northfield, Vermont and have recently noticed that leaves on our sugar maple, and others along this main secondary road, have branches of leaves that are turning brown. They appear to start browning along the edges and work inwards or upwards from where the leaf joins the stem. There are no big spots, just a general browning. The leaves remain flat, not curled even when totally brown. This symptom spreads along a single branch, here and there, as opposed to the entire tree. We thought at first it was due to some earth-moving equipment heat from digging near the tree (new water main going in), but trees that have not come in contact with this equipment have the same problem. Brown leaves seem so symptomatic of many diseases. Any ideas? Thanks very much.

Answer
Sounds like leaf scorch. Maple leaves often show a browning or drying at the outer margin of the leaf or in the areas between the veins in mid to late summer. The areas near the veins generally remain green; however in extreme cases the entire leaf may dry and fall prematurely. This may lead to scorch caused when leaves lose water more rapidly than moisture can be replaced from the soil. This can be caused by too little water in the soil or a physical restriction of the root.

The symptoms of leaf scorch usually appear during hot, dry, windy weather. Trees growing along streets or in areas where the roots are restricted seem to suffer most. The outer parts of leaves or whole leaves dry up. Following such an episode new leaves will often form if moisture supplies to the roots are adequate. Scorch itself seldom kills a tree, but may weaken it to the point where insects or disease can further injure it. Leaf scorch is best controlled by deep watering during dry periods.