Plant Pathology Infobytes
July 22, 1997
Birch Leaf Blight - Responsible for Summer Leaf Drop
The river birch is one of our most popular and versatile members of the Southern landscape. This tree tolerates a variety of locations and is a fast grower. Plus, its rustic bark adds a distinctive appearance which complements other landscape plants.
Another plus for river birch is the fact that it isn't susceptible to many insect or disease problems. About the only problem which affects river birch is leaf blight, a fungus disease which causes summer leaf drop.
Defoliation caused by birch leaf blight has been more extensive this season because our wet, cool spring created conditions favorable for earlier than usual infection of young leaves.
The first symptoms of birch leaf blight include small (barely visible) brown spots on young leaves. The spots appear in early summer and increase in size and number. A distinctive symptom is a yellow "halo" which surround each of the spots. By mid-summer the entire leaf turns pale yellow and falls from the tree.
In seasons when birch leaf blight is severe, it's not unusual for trees to lose thirty to forty percent of their foliage. This leads to a lot of dead leaves beneath trees and homeowner concern about the health of their trees.
Common questions about birch leaf blight include: "Will this disease kill my tree, and what can I do about the problem?"
Don't be concerned about this disease killing your trees, since enough leaves will remain to carry on the job of photosynthesis. Plus, the disease primarily affects leaves, so the causal fungus won't spread to branches and the main trunk to cause problems.
Homeowners who want to make their river birches a bit stronger and better able to withstand this disease next year, should consider collection of soil samples from affected trees. The soil samples can be analyzed to determine fertility need of your trees.
See your county Extension office about the procedure for soil sample collection. It might be that a fall application of phosphorus and potash will be needed. These fertilizer materials will help your tree go into the winter a bit stronger and get off to a better start next spring. Stronger trees are better able to resist diseases such as birch leaf blight.
Also, raking and removal of fallen leaves is a good idea. Diseased leaves which carry-over to next spring will be sources of the fungus which causes the leaf blight. They can be composted and used if the composting is carried out properly.
Other practices include a dormant season application of a lime sulfur spray to your trees this winter, and three or four applications of a maneb fungicide following leaf emergence next spring. These will reduce the amount of birch leaf blight and leaf fall later in the season.
Please feel free to check by your county Extension office for further information on improving the health of your landscape plants.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.