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.
Adapted from: Sadof, C.S. 1993. Keeping up appearances. American Nurseryman 177:(9) 83-85.
