Question
We just noticed that the leaves of our Autumn Blaze maple tree are covered with little raised, red spots--they look like tiny little red balls.  Is this a disease or are they insect eggs of some kind?  Is there an "un-poisonous" way to treat it?  There is a flower garden surrounding the base of the tree.  Thanks.

Answer
These are galls caused by an insect relative a mite. Maple, Acer spp., leaves are often infested with a wide variety of brilliantly colored, odd-shaped galls and blotches. Galls are irregular plant growths which are stimulated by the interaction between plant hormones and growth-regulating chemicals produced by some insects and mites. The maker receives food and protection from the gall tissue. Gall populations fluctuate from year to year, occasionally becoming very abundant. Despite the aesthetic impact and premature leaf drop during outbreaks, tree vigor is not affected significantly.


Some of these abnormal plant cell growths called galls, are caused by very small eriophyid mites in the family Eriophyidae . Members of this family of mites are commonly referred to as eriophyid mites. Several species of eriophyid mites cause leaf galls on maple. They are the maple bladdergall mite, Vasates quadripedes Shimer, maple spindle gall mite, V. aceriscrumena (Riley), and some erineum gall mites, Eriophyes spp.

In general, these galls are not harmful to the health of a tree. The brilliant red color associated with these galls generally alarms some people who believe the trees are 揹iseased?or seriously damaged. Feeding by eriophyid mites appears to stimulate the formation of galls on the upper and lower surface of the leaves. Occasionally, photosynthesis (food making process by plants) may be reduced in individual leaves that are heavily infested. If many leaves on a tree are heavily infested, there may be some reduction in growth.

Application of some formulations of carbaryl (Sevin, etc) are labeled for control of mites on shade trees. However, because the galls do not affect tree health, applications are not necessary. If you want to reduce the population next year--An application of carbaryl (Sevin) or chlorpyrifos (Dursban) to the lower leaf surface when the leaves are about 1/4 expanded and again 10 days later may reduce infestations.


I would worry about the leaf galls. They will not spread to any other plants.