Issue 8, June 11, 2010

Cottony Maple Scale Management

Control of cottony maple scale can be achieved in several ways. Letting nature take its course and allowing the twicestabbed lady beetles to provide control is one option. Another is to apply a crawler spray after the cottony maple scale crawlers hatch about mid-July. Acephate (Orthene), acetamiprid (TriStar), bifenthrin (Talstar, Onyx), cyfluthrin (Tempo), insecticidal soap, malathion, and summer spray oil are all effective crawler sprays.

Before applying a crawler spray, look for the presence of twicestabbed lady beetle adults and larvae on the tree. If there are at least two or three per foot of infested branch, a crawler spray will probably kill the lady beetles and reduce the cottony maple scale about as much as the lady beetles would have if they had not been killed. Do not apply a crawler spray before the eggs hatch or after the crawlers have settled on the leaves. Not only will there be little scale control, but many of the lady beetles will be eliminated, resulting in a higher cottony maple scale infestation than if nothing were done.

Some groups may contend that spraying for adult mosquitoes kills the twicestabbed lady beetles, causing cottony maple scale outbreaks or extended outbreaks. However, cottony maple scale outbreaks in Illinois communities where there is no mosquito spraying occurs in the same years as communities that do have a mosquito spraying program. In the past, cottony maple scale outbreaks ended in the same year in northeastern Illinois communities whether they had adult mosquito spraying programs or not.

Systemic insecticides such as imidacloprid (Merit, Imicide, Pointer, Xytect, others) or dinotefuran (Safari) trunk-sprayed, soil-injected, or trunk-injected according to label directions should provide control of the settled crawlers on the leaves, but we do not have any efficacy data. I would appreciate hearing of any treatment results.

Perhaps the best option is to apply a dormant oil spray during the tree dormant season on a day when the temperature stays above freezing for 24 hours after application. The dormant oil kills about 90% of the overwintering cottony maple scales when the twicestabbed lady beetles are wintering under loose bark where they are not hit by the oil spray.--Phil Nixon

Phil Nixon

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