Be on the lookout for cottony maple scale this time of year

Published 12:00 am Sunday, June 14, 2009

A trip to Inglewood Drive last week to look at a couple of 30-something-year-old maple trees revealed an interesting insect problem — cottony maple scale. Though there are numerous scale insects in our environment, the cottony scale is probably one of the most noticeable this time of year.

It is usually in early June when the cottony scale females lay egg sacs that resemble small pieces of popcorn. These scales also produce large amounts of liquid waste — honeydew — so leaves may be shiny and sticky, and black sooty mold fungus may cover branches and the trunk. Left alone, high numbers of scale insects feeding on a tree lead to thinning foliage, reduced branching and lower photosynthesis — in short, a tree that may soon find itself in the rubbish pile.

Cottony maple scales will not only attack maples but will sometimes feed on box elder, birch, elm and a few other tree species. They spend the winter in the immature stages on the twigs and branches, and are actually completing their development now with the egg sac production. The eggs will hatch over the next several weeks, and the crawlers will spend their summer feeding on sap on the underside of the leaves. Just before the leaves drop in the fall, they will move back to the twigs. There is one generation each year.

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In the past, scale control could be very challenging. Insecticide applications had to be properly timed to match the crawler stage, when the insects were most vulnerable to control. Also, control measures needed to be repeated over several seasons, in many cases, to adequately remove the pests and rescue the trees.

Just like the case involving the pair of maples on Inglewood, scales tend to thrive on less-than-vigorous trees — ones that have slowed in their growth due to age, drought or lack of adequate soil fertility.

Insecticidal treatments such as horticultural oils and insecticidal soaps have been and continue to be used with some effectiveness, as well as some synthetic insecticides. These products may burn the foliage of sensitive plants, such as the Japanese maple, so it is important to check the product label for information about the plant species one intends to treat.

Newer products containing the active ingredient imidacloprid (Bayer Advanced Garden Tree and Shrub Concentrate) add the conven-ience of plant safety as ease of use as they are applied as a soil drench around the roots of infested trees.  This water soluble insecticide is taken up by the roots and transported throughout the plant where it is ingested by the sap-feeding scale insects. This provides a means of scale control without the reliance on foliar sprays. Often, trees are simply too tall for a homeowner to spray.

Once the scale burden is removed from the trees, new foliage will have a much healthier appearance. The sooty mold fungus and shiny honeydew on the leaves should gradually disappear and bud break will occur earlier next spring.

John C. Coccaro is county Extension director. Write to him at 1100-C Grove St., Vicksburg, MS 39180 or call 601-636-5442. E-mail him at