Fruit Crops

Augmentation Biological Control in the Home Orchard

By now, readers of MBCN should realize that there are two primary approaches to biological control: conservation of existing natural enemies and augmentation by making releases of natural enemies. Considerable research has been done on both of these approaches for pest management in commercial orchards. Conservation biological control has been widely utilized and is very important. Augmentation biological control has been shown to be effective in many cases, but often is cost-prohibitive (there are a few exceptions). Those of us who do research on biological control in commercial orchards are often frustrated that sources for funding such research are few and far between. It shouldn't be too surprising, then, to learn that funding for such research in the home garden is almost non-existent. Therefore, when asked what commercial biological controls are effective in the home orchard, we have very little data on what works. But also, we have very little data on what doesn't work. We therefore have to extrapolate from research that has been conducted in commercial orchards. Often, such an extrapolation requires a bit of a leap of faith, because the environments of a home orchard and a commercial orchard are often quite different, and what works in one, may not work in the other. In some regards, augmentation biological control may be more achievable in the home orchard. One reason is economics. Home gardeners are often willing to invest heavily in their gardens, both to assure a bountiful and assumingly safe harvest, but also because gardening is often considered recreation and therefore worthy of some additional investment. With these thoughts (but very little data) in mind, the following are possible options when considering augmentation biological control in the home orchard.

Bacillus thuringiensis is certainly a proven performer. This microbial insecticide is effective against foliage and fruit feeding caterpillars such as cankerworms, tent caterpillars, fall webworms, leafrollers, and fruitworms. The residual period of activity after application is very short, and multiple applications may be necessary. Sprays should be timed to control young larvae. Bt will not be useful against interior-feeding caterpillars, such as leafminers, or codling moth larvae inside of fruit.

Insect parasitic nematodes may provide some benefit against insects that spend some of their life in the soil (such as plum curculio and apple maggot), but there has been little research on such applications in orchards.

Of the commercially available parasites, Trichogramma has the greatest potential. Several species are available; T. platneri is often most recommended for use against tree-dwelling pests, but ask your supplier for recommendations. Potential targets include codling moth and leafrollers. High release rates are necessary because the tiny parasitic wasps can rapidly disperse from release sites -- a problem when trying to cover small areas. Also, remember that the egg is the target stage and therefore releases have to be properly timed.

Green lacewings are generalist predators that will feed on many pests, including aphids, scale crawlers, spider mites, and small caterpillars. I recommend applying them as eggs, which are the easiest stage to handle. Two or three releases during the growing season will help control many types of pests.

Spider mites are often not problems in home orchards, but if these are of concern, predatory phytoseiid mites are effective predators. They are rather expensive to use -- check with suppliers for suggested species, release rates and prices. Releases should be made shortly after the end of the blossom period. Most of the above suggestions relate to the control of leaf-feeding pests.

Regrettably there are very few options for biological control of serious fruit-feeding insects such as codling moth, plum curculio, and apple maggot. Some non-chemical methods are available for these pests, such as limb-jarring for plum curculio and trapping of apple maggot (information on these methods are available from many extension offices). If it is necessary to use broad spectrum insecticides, remember that these may interfere with the activity of predatory or parasitic insects that have been released into the orchard.

- Dan Mahr, University of Wisconsin - Madison


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