Yard and Garden -06-19-2010 - Ted Griess / Extension Horticulture Assistant

“What’s bugging you?” is a question people often ask when they notice someone is upset. Lately, I have encountered a number of upset people, and interestingly bugs are causing all the bugging. To the entomologist, the correct word is insects, but for today, I am sticking with bugs. Although mentally bugging people, these little critters are physically bugging trees and one particular tree species bugged the most is silver maple.

Homeowners are noticing small, wart-like bumps covering the upper surface of their silver maple leaves. These little bumps are commonly known as maple bladder galls. Galls are defined as abnormal growths or swellings of plant tissue caused by an attack from assorted living organisms. The attacker could be an insect (bug) as well as a mite, nematode, bacteria, fungi or even a virus.

Maple bladder galls first appear yellowish-green in color, then red and finally black. The little critters causing the bumps are tiny, microscopic mites called Vasates quadripede. Mites belong to the class Arachnida, which includes spiders as well all other eight-legged creatures, but for this article, I will call them bugs. When this minuscule, menacing mite bites into a leaf, it injects a growth hormone causing abnormal tissue to form — a gall. Surrounding this little bug, the gall provides protection from adverse weather, predators and parasites. Inside it feeds and lays eggs for the next generation. Once galls form little can be done to rid the plant of them. The good news ― as unsightly as galls are— they do little, if any, damage to the tree. To avoid being bugged by these unsightly leaves next year, apply a dormant oil spray to the branches and the trunk in early spring before the buds open.

If you are also discovering that the underside of the leaves and the stems and branches of your silver maple tree are covered with a white, cottony mass, you have another bug problem. This time it is Icerya purchasi, more commonly known as cottony cushion scale. With many people’s trees experiencing this problem, and I not being overly familiar with it, I sought the expert advice from Dr. Fred Baxendale. Fred is an extension entomologist with UNL and a regular panel member of the Backyard Farmer television show, sponsored by Nebraska Educational Television and UNL Extension. Dr. Baxendale’s response to me was as follows:

“Ted, this cottony cushion scale is one of the largest and most conspicuous on ornamental plants. The two most important host plants are silver maple and hackberry. This insect will infest apple, box elder, dogwood, poplar, oak, willow, linden, elm, many shrubs, and stone fruits. Winter is spent as a flat, oval, immature female about the color of the host plant twigs. Overwintered females mature in the spring and deposit eggs in late May and June. Eggs are laid in a white, cottony mass that extends from the female scale. At this stage, scales may be five to six millimeters long. Crawlers begin to emerge in late June and July and move to undersides of leaves to feed during the summer. In the fall, they move back to twigs and small branches to overwinter. There is one generation per year. While large and showy, cottony cushion scale rarely causes significant injury to trees. However, if treatment is desired, apply dormant oil sprays before bud break to kill overwintering stages. Residual sprays are most effective during the crawler stage. Thorough coverage is important. Trunk injections are also available. Fred”

Now that I have armed you with a little knowledge about what might be bugging your maple trees, maybe you yourself will be less bugged. I certainly hope so.