Insecticide Resistance Monitoring

The incidence of unacceptable levels of codling moth infested fruit at harvest is on the rise in Michigan, especially in the fruit ridge area and in southwest Michigan. Failures to control CM can theoretically be attributed to several different factors including less than optimum timing, inadequate coverage, or a reduction in susceptibility to insecticides. Lack of control due to resistance is the most difficult one for growers to address without technical assistance. The tree fruit program at MSU is working closely with growers and consultants to identify orchards and production areas where CM resistance to azinphosmethyl is a major cause of poor control. A topical pheromone trap bioassay is being used to assess the susceptibility of CM populations to this compound. The trap bioassay provides consistent results and is fairly simple to conduct, thus providing a means of testing populations from many orchards over the course of a season. In addition, laboratory bioassays are being conducted on CM collected from commercial orchards experiencing control failure to determine if the effectiveness of alternative insecticide compounds is also in jeopardy. This information will assist apple growers as they develop reliable CM resistance management programs.

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