This is a fungal disease that affects plum trees. The disease is usually caused by the fungus Taphrina communis, and sometimes by the fungus Taphrina pruni. Infection occurs shortly after blossoms open, but is not evident on fruits until they are 6-12 mm in diameter. The infection first shows up on the fruit as raised, spongy greenish white spots. These spots spread quickly until they often cover the entire plum. Next the plum swells quickly to three or four times its normal size. The plum becomes hollow, withering and lacking seeds. Its surface becomes leathery and covered in a grayish white powder. Spores are dispersed, and then the fruit darkens, and falls. Affected twigs are swollen and distorted, leaves are malformed and curled.
Treatment of this disease must begin early in the season. Once symptoms appear on the crop it is too late to save the fruit for this year. Practice sanitation for the season in order to minimize next year’s infection, this is done by removing all infected plant material and disposing of it. The next spring begin treatment early by spraying the tree with a copper spray such as Later’s Copper just as the flower buds begin to swell. Spray the entire tree, especially the buds and twigs, using a high-pressure spray. This should be done on a day that is above four degrees C. The spraying should be repeated two more times at weekly intervals. This problem is most problematic in wet spring years.
As a preventative measure, many people like to spray their trees with a copper fungicide once every fall and once every spring. This will help to guard your trees against fungal infections.
By Dr. Bill Paton and Laura Tilley