Balanced Pest Management Focuses on Natural Predators
INTEGRATED pest management (IPM) is highly effective, generally cheaper over the short term, and over the long term, far cheaper than the all-spray approach. And ``it's getting easier all the time,'' says Sheila Daar of Bio-Integral Resource Center in Berkeley, Calif. Her message to a recent gathering of Massachusetts nurserymen was direct and powerful. ``When we kill off the beneficials [natural enemies of pests] we inherit their work,'' Mrs. Daar says. ``And, it seems, we don't do it nearly so well.
Contrary to popular myth, IPM ``does not ban the use of all chemicals,'' she says. There is a place for pesticides (both artificial and natural), but they are invariably the last resort, seldom the first resort, and never the only resort.
``If pests have reached epidemic proportions before we are called in, we spray right away,'' says Daar. But the spray is ``target specific'' (so that non-pest insects will not be destroyed). Where target-specific pesticides are not available, ``we use one that loses its potency fairly quickly, at which stage we introduce the natural enemies of the pest and they take over from then on.''
It is the broad-spectrum, kill-everything-in-sight pesticides that Daar deplores. They create more problems than they solve, she says. Take the famous cherry trees in Washington, D.C. A few years back they were badly damaged each year by white peach scale, which can eventually kill the trees.
Under normal conditions the scale is seldom a problem, because it is readily checked by a commonplace microscopic wasp that lays its eggs in the pest. The National Park Service had been spraying powerful insecticides to eradicate Japanese beetles and tent caterpillars in Washington each spring. These sprays also knocked out the tiny wasp, which meant that in summer the scale, resistant to the sprays, enjoyed a field day.
The problem was solved when the Japanese beetle was treated with a host-specific biological control that attacks the beetle in its larval stage in the turf, while the readily seen tent caterpillar outbreaks were simply pruned out of the trees. This allowed the wasp population to reestablish itself. The scale is no longer a major problem.
This type of situation is repeated many thousands of times all over the country each year, Daar says. Destructive spider mites surface in warm summer weather on fruit trees and ornamentals, she points out, because spring spraying for caterpillars has eliminated the predators of the destructive pest.
As entomologists learn more about the life cycles of both pests and predators, IPM is becoming more effective, Daar notes. Of specific programs she is involved with, she says, ``If the work's not getting easier and easier, and less expensive [as the program continues], I know I'm doing something wrong.''