Effects of cover sprays and residual pesticides on scale insects and natural enemies in urban forests

The authors "report findings of studies that examined the effects of cover sprays and the use of residual pesticides on scale insects and natural enemies found in the canopies of trees and shrubs in urban forests in Maryland, U.S. The first study investigated the effect of long-term application of insecticides on populations of armored scale insects associated with woody landscape plants in residential settings. The second study examined the effect of residual insecticides on the community of natural enemies that populate tree canopies in an institutional landscape." Co-authors are: J.J. Holmes, C. Sadof, P. Shrewsbury, and J.A. Davidson. [UMN]

"Cover sprays and residual insecticides are tactics used by landscapers and arborists to control arthropod pests on trees and shrubs in urban settings. Trees in residential landscapes that received three cover sprays annually for at least 4 years harbored a greater diversity of scale insect pests and were much more likely to be infested with scales than trees in landscapes treated with cover sprays for shorter periods of time. Oak (Quercus palustris) trees in an institutional landscape treated with residual insecticides harbored significantly lower numbers of beneficial arthropods than trees treated with a pesticide that lacked residual activity. The suppressive effect of the residual insecticides on natural enemies was pronounced on the community of parasitic wasps that attack the obscure scale (Melanaspis obscura), a common scale insect pest of oak. The effect of residual insecticides on individual wasp species persisted 4 weeks after the pesticides were applied. By reducing the use of cover sprays and residual insecticides, arborists may be able to conserve communities of natural enemies in managed landscapes. This will enhance the biological diversity of beneficial insects found in urban forests and thereby aid in increasing their sustainability." [Abstract]

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