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Peggy Sellers and Karen Rane
|Jumping Oak Leaf Galls||Jumping Oak Leaf Galls Magnified|
The Plant and Pest Diagnostic Laboratory (P&PDL) received white oak samples from southern Indiana with these symptoms. On the upper surface of the leaves, small (1/16 to 1/8 inch diameter) brown spots with yellow haloes are evident. The undersides of the brown spots on these leaves have small galls, each containing an insect. These galls are similar to a type of jumping oak gall, however, Dr. Cliff Sadof, extension entomologist, could not identify the species of the insect based on the juvenile stage inside the gall.
Jumping oak galls are produced by gall wasps. According to Johnson and Lyon (Insects That Feed on Trees and Shrubs, 1991, page 440), as the larva inside of a gall matures, the gall falls to the ground. The gall then "jumps" repeatedly a few centimeters because of the activity of the insect inside.
According to Dr. Sadof, leaf galls rarely have a significant impact on the health of affected trees. This problem, however, appears to be responsible for a significant amount of necrosis and leaf scorch in samples we have received in the P&PDL. Cultural practices that aim at reducing plants stress (watering during dry periods, avoiding root disturbances) will help trees maintain their vitality.
Plant and Pest Digital Library and Digitally Assisted Diagnosis, Purdue University, West Lafayette, Indiana.