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.
CPB resistance and diapause. We do not know whether resistance acceleration may be occurring as later emerging portions of CPB populations are exposed to sub-lethal, systemic insecticide doses. A proportion of populations may be selected for later emergence when, or if, in-plant insecticide levels decline. Over time, the continual exposure of late emerging insects to sub-lethal doses will aid in hastening resistance development. The long term impacts of a protracted emergence are currently unknown and may compromise the efficacy of current and future systemic registrations. Field experiments in 2010 were set up to investigate the extent to which extended diapause or delayed emergence is associated with insensitivity among populations. Specifically, experiments consisted of caged beetles (approximately 500-1,000 adult CPB / cage) collected from sites with measured levels of neonicotinoid resistance and compared with sites possessing no evidence for insensitivity. To date, we have observed unique differences in the emergence phenology of populations collected from different locations each with unique estimated resistance ratios. During the fall, winter, and spring of 2011-12, we will again monitor the temporal patterns of adult emergence. Here again, populations will be collected from sites with a documented history of CPB resistance associated with elevated resistance ratios and the associated emergence phenology will be examined over the emergence interval.
Efficacy of Insecticides. The objective of this experiment was to assess the efficacy of foliar insecticides applied to control insect pests in potato. The trial consisted of 38 main effect treatments arranged in a randomized complete block design (RCBD) with four experimental replicates. Potato was machine planted on 26 April 2012 at the Hancock Agricultural Research Station in central Wisconsin. Experimental plots consisted of 2 row plots measuring 6 ft wide and 20 ft in length with unplanted guard rows on each side. Rows were planted on 36 inch row centers with 12 inches between plants with 12 ft alleys separating replications. All foliar treatments were applied at 20 gallons per acre (gpa) using a four nozzle, 6 foot boom equipped with a flat fan spray tip powered by a CO2 backpack sprayer operating at 30 pounds per square inch (psi). Foliar treatments were applied twice in succession when 75-90% of the first generation Colorado potato beetle (CPB) was within the first and second stadia. Foliar applications of novaluron were initiated 7 June 2012, one week earlier than all other treatments. The first foliar application occurred between 7:45am – 8:30am hours on 14 June 2012, and application conditions were recorded as a southwest wind at 9.2 mph, 60.1°F (15.6°C), 51% RH, under clear skies. A second application occurred on 21 June 2012 between the hours of 7:00am and 8:00am. Application conditions were recorded as a west wind at 8.1 mph, 64°F (17.8°C), 87% RH, under cloudy skies. All plots were maintained according to standard commercial practices. CPB adults (AD), egg masses (EM), small larvae (SL), large larvae (LL) as well as potato leaf hopper (PLH) adults and nymphs were assessed by counting the number of each life stage on 10 randomly selected plants from the center two rows in each plot. CPB counts occurred five times during June and July. The first set of counts occurred on 18 and 21 June 2012 after the first application. The second set of counts occurred on 28 June 2012, 3 and 10 July after the second application. PLH counts were performed on the same 5 dates. Count data were log10 transformed prior to analysis. Means were separated using the least squared difference option in an analysis of variance (ANOVA). Populations of CPB were already established by the first foliar application, as defoliation estimates approached 5% in most plots. Experimental treatments were often significantly different than untreated check in the control of CPB adult, larval, and associated defoliation, although some treatments were more effective at controlling immature CPB. Adult PLH pressure was moderate, and the neonicotinoid containing compounds plus the synthetic pyrethroids provided the most effective control of PLH adults. No signs of phototoxicity were observed. This research relates to objectives 1 and 3 through neonicotinoid bioassays and efficacy of insecticides.