Galls are ugly growths, but they don't kill your tree

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/

The Future of Tropical Forests

Source: Biological Conservation Newsletter

Tropical rainforests are among the most species rich regions of the world. If current deforestation and habitat loss continues, a mass extinction of forest species is predicted in these areas. Smithsonian Tropical Research Institute scientist S. Joseph Wright and Helene Muller-Landau from the University of Minnesota have recently conducted a survey of human population trends and forest cover.

Wright and Muller-Landau use present-day relationships between forest cover and population density and United Nations population projections to predict future forest cover for tropical African, American and Asian countries. United Nations population projections generally predict that human population growth rates will decline and that urbanization will intensify. Wright and Muller-Landau predict future forest cover using both an optimistic scenario based on rural populations alone and a pessimistic scenario based on total (rural plus urban) populations.

Continental trends suggest that deforestation will decrease and a larger area will remain forested in the Americas where population growth is slowing most rapidly and urbanization continues to increase. The outlook is not as optimistic in Asia and Africa. Asian forests are already quite diminished and populations are growing at a higher rate. In Africa, however, population growth overall and particularly in rural areas continues to increase, and net deforestation is expected to continue.

This research suggests that global deforestation will decrease, regeneration of forested areas will increase and a mass extinction of rainforest species can be avoided. Wright and Muller-Landau hope their research will stimulate more sophisticated predictions of future forest cover. In the meantime, further research is needed to establish the threat to individual species and determine which global, regional or local factors may influence these threats. This research will improve the ability to evaluate and manage human influences on forest species.(+)