Location: Vegetable Crops Research Unit
2013 Annual Report
Efficacy of alternative insecticides. Preliminary research with the novel insecticide tolfenpyrad has shown a high level of toxicity to CPB larvae and adults in the lab and field. In 2012, we will conduct bioassays to measure LC50 levels and to determine optimal rates of this chemical to use in the field. In addition, we will evaluate the efficacy of several other novel insecticides including cyantraniliprole, spinetoram, and others.
Plant resistance. We will identify and compare chemicals emitted into the headspace of wild relatives of the cultivated potato that show various levels of resistance to CPB. Volatiles that are specific to and are abundantly produced by CPB resistant Solanum species will be evaluated for CPB behavior modifying activity. Wild species clones selected for the production of behavior modifying volatiles will be crossed to the cultivated potato. The hybrid offspring will be selected for adaptation, fertility and resistance to CPB. Resistance bioassays will be carried out in the laboratory and the field. We will identify volatiles from resistant plants and use this to inform potato breeders about an unattractive or repellent potato volatile profile, which can be combined with traits that reduce CPB development, increase CPB mortality and slow the development of insecticide resistance. Our ultimate goal is to combine multiple resistance mechanisms into a clone that delays CPB resistance development and provides long lasting broad-spectrum crop protection.
In general, resistance values across the country are very similar to those in recent years. As long as growers continue to use a variety of insecticide modes of action when managing Colorado potato beetles, it appears that the neonicotinoids can continue to play a major role. Most importantly, it is essential that growers refrain from using foliar products containing neonicotinoids, when a neonicotinoid was applied at planting.
How the research relates to objective 3: We tested the Colorado potato beetle’s ability to develop resistance to insecticides which makes it very important to continue testing the efficacy of both new insecticide chemistries and existing compounds. Such tests provide data on comparative effectiveness of products and data to help support future registrations and use recommendations in Michigan. Except for imidacloprid and bifenthrin+abamectin, all treatments resulted in significantly fewer small larvae than the untreated control, while all treatments significantly reduced the number of large larvae per plant, compared to the untreated. There were also significant differences in numbers of large larvae among the insecticide treatments. All three systemic products, one with imidacloprid and two with thiamethoxam as the active ingredient, performed well, with the experimental product containing thiamtehoxam having significantly fewer large larvae than six of the foliar products. Among the foliar products imidacloprid, required weekly sprays, while an experimental product and the low rate of tolfenpyrad were applied three of the four weeks. Bifenthrin+abamectin, spinosad and the high rate of tolfenpyrad required one subsequent application, all two weeks after the initial application. Of these, however, only spinosad provided reduction in average large larvae below the threshold of one per plant. Despite one fewer application for the high rate of tolfenpyrad, no significant differences in beetle life stages or defoliation were noted between the high and low rates for this product. All three cyazypyr treatments required only the initial foliar application to provide first generation beetle control. The untreated plots had significantly greater defoliation compared to all other treatments. The seasonal defoliation average was 36.6% in the untreated plots, compared to less than 6% for all other treatments. Differences in defoliation among insecticide treated plots ranged from 1.1 to 5.9%. Neonicotinoid insecticides are still providing sufficient Colorado potato beetle control for Michigan farmers, but new chemistries are also proving to be effective.
How the research relates to objective 4: Plant resistance was measured on different Solanum accessions/clones. Resistance was measured by placing 5 small larvae on a plant leaf, which was placed in a petri-dish and left at room temperature. The survival, growth stage, and plant leaf area (%) was estimated daily for two days. We have found that accession 88-92 were highly resistant to small Colorado potato beetle larvae. Headspace volatile analysis of the different Solanum clones showed that the clones that exhibited resistance against small Colorado potato beetle larvae had similar headspace composition. Some of the compounds that characterized the headspace of these clones were geraniol, nonanal, methyl salicylate, and benzene acetic acid. These compounds are known from other plants because of their ability to repel insects or reduce feeding.