Plant Pathology Infobytes

August 13, 1998
Don't Lose Your Apple Crop to Bitter Rot

Many home orchardists have a good chance of harvesting a bumper apple crop this summer and early fall, provided diseases such as bitter rot are controlled. Orchardists who've managed to keep this disease in check to this point in the season, should continue fungicide applications since now is a critical time for controlling bitter rot.

Although the fungus which causes bitter rot is active earlier in the year, this disease doesn't really takes off until fruit are about half mature. Following rainfall, fruit infection occurs, and by the time fruit begin to mature, bitter rot is often in an advanced stage on many fruit over the tree.

Fruit infection shows up as slightly sunken, circular brown spots that are surrounded by a reddish halo. When the spot increases to about an inch in diameter, spore-bearing structures appear in concentric circles on the surface of the spot. A brown decay beneath the diseased spot extends toward the fruit core in the shape of a cone. Within a short time, rot completely and fall from the tree.

To protect fruit from bitter rot infection, continue fungicide spray applications with captan fungicide. Several applications of captan, seven to ten days apart, will be needed in order to fully protect fruit from infection until maturity is reached. Other fungicides, such as Bordeaux Mixture, are also approved for apple bitter rot control and should be available at garden and farm supply stores. Read and follow all application directions present on the fungicide label.


Written by the late Dr. Frank Killebrew

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