One of the advantages of Bt is its specific mode of action. As W.S. Cranshaw, Extension entomologist at Colorado State University, notes, “The activity of Bt is considered highly beneficial. Unlike most insecticides, Bt insecticides do not have a broad spectrum of activity, so they do not kill beneficial insects. This includes the natural enemies of insects (predators and parasites), as well as beneficial pollinators, such as honeybees.” Therefore, Cranshaw says, Bt integrates well with other natural controls in an organic program. For example, in Colorado, Bt to control corn borers in field corn has been stimulated by its ability to often avoid later spider mite problems. Mite outbreaks commonly result following destruction of their natural enemies by less selective treatments.
For organic growers, the maintenance of both beneficial insects and habitats is a one-two punch. The results of a national survey of more than 1,000 organic farmers conducted by the Organic Farming Research Foundation (OFRF) indicates that organic farmers follow the principle that organic farming is a management system by applying inputs to supplement cultural practices. As such, organic growers rely heavily on cultural strategies including beneficial habitats, crop rotation, and resistant varieties. According to Brian Baker at the Organic Materials Review Institute (as part of the Organic Farming Compliance Handbook), Bt is reported as the most commonly used insect control tool, followed by insecticidal soap. In fact, these materials were the only ones used by more than half of all growers responding to the survey.
The end result? If growers can follow through on the use of Bts, they will allow beneficials to thrive and serve their purpose in controlling target pests.