Nursery, Greenhouse, and Landscape News

Conserve Natural Enemies in Landscapes With Site Specific Needs

Ornamental plants are grown and maintained to enhance the appearance and value of the managed landscape. Because perception of plant appearance is subjective, levels of acceptable appearance will vary with location of the plant in the landscape. Consequently, acceptable densities of pests will vary. Understanding the factors that influence these levels of acceptable appearance can maximize opportunities for biological control by conserving natural enemies. Consider, for example, the effects of green peach aphids on a flowering crabapple in the landscape. Heavy infestations cause shoot tips to curl and will coat leaves with sticky honeydew and black sooty mold. Experience in Indiana landscapes shows that predators including lady beetles and syrphid flies are usually found on crabapples within two weeks after aphid populations are detected. Although some leaf curl and honeydew has accumulated by this time, the natural enemies of these aphids usually consume most of the population on the trees within the next 2-4 weeks. If this tree is located in a turf area several yards away from high traffic areas, the curled leaves and honeydew that accumulates in this time is likely to be tolerated. However, if the tree is located near an entryway of a home or over a picnic bench, the accumulated honeydew on the leaves and below the tree is likely to be a nuisance. In this situation some intervention, such as a pesticide application, may be required. Managing aphids on these trees is simply a matter of recognizing the specific needs for the plant in its location.

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