13-year cicadas arriving, leaves dropping

By John Fulton

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[June 08, 2011]  Periodical cicadas have arrived -- Even though Logan County is not in the heart of the territory of the periodical 13-year cicada, there may be spots experiencing the problem. Most of Sangamon County is in the expected zone, while a map for possible emergence indicates only the Chestnut and Latham areas of Logan County.

There are two types of cicadas. The first is the "dog-day" cicada, which occurs in the heat of summer each year. The second is the periodical type that hatches in late May, based on soil temperatures, every 13 or 17 years.

The 13-year brood of Brood XIX is up this year, and numbers may be impressive in some areas. They have already created stirrings to the south and east. Prime areas would be heavily wooded for a period of many years. Numbers can average over 130,000 per acre.

The adult cicada is about an inch and a half long, dark in color, and has red or orange eyes. The female uses an ovipositor like a saw to make slits in small twigs of trees. She then lays eggs in the slits. When the eggs hatch, the nymphs fall to the ground. They then tunnel into the ground, where they find a tree root to suck sap from for 13 or 17 years.

The root-feeding activities are not the most damaging, but the egg-laying slits can cause severe damage to young trees. Young transplants up to 2 1/2 inches in diameter can have their main trunk damaged to the point it will snap. On mature trees, there is little danger of the tree dying from the damage, but many branch ends will break off in windstorms. The favored twig or trunk sizes are three-sixteenths of an inch to an inch and a half.

To protect young trees, or valuable small trees, a mechanical barrier is the most effective. Something like screen wire wrapped around the trunk will prevent damage. Insecticides will also kill many of the cicadas, but it takes only one female to do the damage. Sevin, permethrin or bifenthrin should show some effectiveness.

The other phenomenon that will occur is that traditional predator numbers, such as cicada killer wasp numbers, will also greatly increase. These are extremely large wasps that paralyze the cicada, bury it in the ground and lay eggs in it. The insecticides mentioned previously will also be effective against the wasps. Remember, though, the wasps are actually beneficial. Control should be done only in very high-traffic areas and children's play areas when the wasps become a hazard.

Leaf drop

As anticipated, many of the leaf diseases, such as anthracnose and apple scab, are causing problems. These problems include many leaves dropping from trees. Currently apples, crab apples, sycamores, maples and many other good-quality shade trees are affected. The maple group will accelerate even more in the near future, as they are just entering the worst of the phases.

What starts as spots eventually leads to more dead material in the leaf and leaf stem. At times, especially on apples and crab apples, the leaves then turn yellow. The dead areas cause the leaves to be weak and weakly attached. With some wind, the leaves then fall to the ground.

While it may look like fall, most shade trees will then put out another set of leaves in four to six weeks. The apples and crab apples tend not to initiate new leaves as easily and may remain without leaves for a portion of the summer. The major problem is the loss of the food that these leaves would make for the tree.

Since treatment is not effective once you see the problem, a fertilizer program would be in order. Fertilize at the lawn rate of 8 pounds of 12-12-12 or 13-13-13 per 1,000 square feet. This would be in the drip area in the case of trees. Then, just scatter the fertilizer on top of the ground. You may water if it doesn't rain for a day or two after the application.

[By JOHN FULTON, University of Illinois Extension]

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