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Scouting Watch

June 7, 2006

Cottony maple scale has produced their large, white egg masses in Ogle County and other areas of northern Illinois. These eggs will hatch in a couple of weeks into light gray crawlers that will crawl out onto the leaves to feed until fall. Crawler sprays are effective but kill the beneficial twice-stabbed lady beetle. See the article on this insect in the May 18, 2005, issue of this newsletter for details.

Fungus-attacked anthomyiid flies are being found on the end of the branches of trees and shrubs. Anthomyiid flies are gray and look like house flies but slightly smaller. Many of them are leafminers or root feeders in the larval stage, and they are not generally considered to be pests of ornamental plants. They are attacked by a fungus that apparently causes the fly to crawl to the end of the branch before it dies from the fungus. It hangs onto the branch as it dies and then white fungal hyphae grow out of the insect and further attach it to the branch. Presumably, this allows the spores of the fungus to be spread on the wind more effectively. In some years, these dead flies on the ends of branches are so numerous that the plants appear to be attacked by them. Obviously, there is no damage caused by or control needed for dead flies. If you have a client that requires their removal, they are usually attached too tightly to be knocked off with a water spray. They usually require hand-removal.

Black vine weevil adult damage has been found in northern Illinois. The adults eat semicircular and elongated notches out of leaf margins of yew, euonymus, clematis, and many other plants. Larvae feed on roots of yew, pruning off smaller roots and eating through bark of larger roots. They cause dieback and plant death in nurseries. In landscapes, they are usually not numerous enough to cause serious root damage, so control is usually not needed there. Only females are known of this insect, and they must feed for about 2 weeks before they can lay eggs. During this time, they are susceptible to acephate (Orthene), befenthrin (Talstar), and cyfluthrin (Tempo). Because the adults hide in the leaf litter on the soil, spray the foliage heavily to allow the insecticide to run off into the leaf litter. Be sure to use enough pressure to penetrate interior foliage, where most of the feeding on yew occurs. Because adults emerge over a period of time, spray three times at 2-week intervals to obtain a high level of control.

Author: Morton Arboretum Phil Nixon


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