Sault Star (ON)|Wed 28 Jun 2006
Byline: Katherine Nystrom
You may have noticed wart- and/or pile-like growths mostly on the upper surface of your maple leaves, especially on silver and red maple.
These growths are actually galls and are caused by the presence of tiny mites, called eriophyed mites, feeding on the surface of the affected leaf. The galls, which provide food and shelter to the developing stages of the mites, are green when newly formed but gradually turn red and finally blacken over time. If these galls are numerous they can deform a leaf and mar the overall appearance of the tree. These galls, even when numerous, will not kill a tree. However, when they are plentiful on a young tree growth development can be slowed.
Several species of eriophyid mites cause galls on maple leaves. The maple bladdergall mite, Vasates quadripedes, can be found on silver and red maples. Finger-like galls seen on sugar maple are the maple spindlegall mite, Vasates aceriscrumena. The red pile mite gall, caused by the mite Aceria elongatus, can be found on either side of the leaves of various maples and is felt-like in appearance.
The microscopic adults overwinter, or spend the winter, in niches on the trunk and branches of maple trees. When the leaf buds begin to expand the adult mites move to the leaves and feed there. Abnormal cell development is initiated and as a result the female becomes enclosed in a characteristic structure or gall. Eggs are laid in the galls; they hatch, feed through several larval stages, and become adults in a matter of weeks. These adults leave the gall and may initiate other galls if suitable developing leaf tissue is present.
The number of galls fluctuates widely from year to year. Except in young or newly planted trees, the loss of leaf surface is insignificant and control is unnecessary. If need be the early handpicking of damaged leaves, which are frequently most common on the lower branches, will help to keep populations down. If it is desirable to prevent damage on young or newly transplanted maple trees, dormant oil can be used before bud-break in the early spring. Dormant oil should not be used on Japanese or sugar maple to avoid injury.
REMEMBER: Insecticides, by their very nature, are designed to control insects. Because of this, persons using insecticides must ensure they use them correctly. Always read the product label prior to using the product. Ensure that the product is registered for the target insect and follow label specifications for mixing, application rates, and disposal and safety precautions.
The preceding information is provided by the Sault Ste. Marie laboratory of the Canadian Forest Service of Natural Resources Canada, where Kathryn Nystrom is employed as an insect identification officer. While we cannot guarantee a response to each inquiry, we will make every effort to respond to readers= questions, either through this column or individually. Direct inquiries to: Tree Talk, c/o Communications Officer, Great Lakes Forestry Centre, P.O. Box 490, Sault Ste. Marie, Ontario P6A 5M7. Visit our Web Site at http://www.glfc.cfs.nrcan.gc.ca/
