Fruit Crops

Impact of IGRs on Beneficials in Apple

There is considerable interest amongst IPM practitioners in replacing broad-spectrum insecticides, which often have adverse effects on beneficial predators and parasites, with more selective pesticides. One class of insecticides that is receiving some attention is the insect growth regulators (IGRs). Although the overall action of IGRs is to interefere with normal growth and development of the insect, different specific materials have different chemical and biological properties. Some of the products are at least somewhat selective in what they kill. Although few IGRs are currently in use on food crops in the U.S., several are in development and it is likely they will play a greater role in pest management in the future.

Australian entomologists have evaluated two IGRs for their effectiveness against codling moth and other pests of apple, and for their impact on predators in the orchard. Tebufenozide and fenoxycarb were compared with the commonly-used broad-spectrum organophosphate, azinphos-methyl. Fruit damage was very low and equivalent across the three treatments. However, in both years of the study, spider mite levels were higher in the azinphos-methyl treatments than in either of the IGRs. The differences in pest mites could not be attributed to predatory mites, because the levels of these were comparable in all three treatments. However, spiders, a predatory bug, and the mite-predatory beetle Stethorus all were significantly reduced in the azinphos-methyl treatments compared to the IGRs. The authors of this study conclude that the two IGRs tested could provide good target pest control while fitting into a mite IPM program.

The two products tested in Australia are not currently registered for use on apple in the U.S. Further, other studies have shown that there may be negative impacts of specific IGRs on specific beneficials, indicating that each situation may have to be studied individually. However, it does appear that the IGRs as a group may have a future role in conserving beneficials in apple IPM programs.

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