Plant Pathology Infobytes

September 3, 1998
Leaf Blight and River Birch Leaf Shed

"What's wrong with my river birch? The leaves are shedding and by the end of the summer, I probably won't have any foliage left on my tree." This is a question many Extension Offices are receiving from homeowners concerned about the health status of their river birches.

The river birch is one of the most popular southern landscape trees. This species 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 disease which affects river birch is leaf blight which causes summer leaf drop.

Defoliation caused by birch leaf blight has been extensive this year primarily because of early season "El Nino" wet conditions which favored infection of young leaves by the birch leaf blight fungus.

The first symptoms of birch leaf blight include small (barely visible) brown to black 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 to late-summer, infected leaves turn pale yellow and fall 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 whether the disease will kill affected trees.

While river birch leaf blight is unsightly and causes premature leaf drop, 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. And the disease won't spread to other tree species or landscape plants.

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 needs of your trees, since well-fed plants are better able to withstand the effects of diseases.

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 the County Extension Office for further information on improving the health of your landscape plants.


Written by the late Dr. Frank Killebrew

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