By Tom Marshall
In July strange growths were found on the underside of some of the leaves of my four year old native American plum tree. Each one looked like a little cigar shaped dark green tubular leaf on a small lighter green stem. They ranged in length from1/4 to 3/4 inches. I brought some affected leaves to Tami Schlies’ orchard tour on June 22 and the members present, representing a wide distribution of orchard experience, had not seen this type of gall.
Later an entomologist with the USDA found a very small white larva in one of the galls and showed it to me. It was only about 1/250th of an inch long, but was clearly visible wiggling away under a 50 power binocular microscope. A plant pathologist found a colored picture of a sugar maple leaf with galls that looked identical to the galls on my plum tree. They were called spindle galls and were caused by the insect Verates aceriscrumena.
A possible connection between the maple and the plum tree might be that my plum tree was purchased from a New York State nursery, a maple sugar producing area. Once the affected leaves were picked, the galls did not spread and the plum tree is very vigorous. I will gather and burn all plum leaves this fall. I also froze some of the specimens on the leaves they infected for future research.