Question
I have 4 25foot tall Autumn blaze maples in my yard i planted 2 yrs ago. I noticed 2 of them have little red balls covering the leaves. What is this, what can I do? Thanks

Answer
Thess are leaf galls. The upper surface of silver and red maple leaves often become covered with small, red, round wart-like structures about 1/16 to 1/8-inch in diameter. These are maple bladder galls caused by a small mite, Vasates quadripedes (Shimer). The structures are generally noticed first in May, about the time the leaves have become fully expanded. At first the galls are green but they quickly turn pink to red and eventually black. Leaves frequently become so covered with the galls that they completely twist out of shape and may even drop early.

maple bladder gall mites overwinter as free living mites under loosened bark and around the callous growth of wounds, scars and pruned branches. These overwintered forms produce the gall forming stage in early spring. When the maple leaves first appear, the mites migrate to expanding buds and begin to feed on the undersurface of leaf buds. This causes the formation of a blister which expands into a hollow bladder or spindle as the leaf expands. The mites enter the cavity and continue to feed within its protective walls. This stage reproduces asexually within the galls and the new mites mature by late June to mid-July. At this time the galls dry out and the tiny entrance hole opens up to allow escape of the mites. These mites then seek out overwintering sites.


Other than the mere aesthetic damage and possible early leaf drop, no significant damage is done to the health of maple trees. Following a mild winter, damage from these leaf galls can be excessive but affected trees often send out new leaves to replace the damaged ones. Since these leaf galls of maple do not cause any real harm to the trees, control measures are not generally needed.