EVALUATION OF IN-FURROW AND FOLIAR MATERIALS TO CONTROL CPB IN POTATOES, 1998: Potatoes were planted on 1 Apr at the Eastern.
(E73) POTATO: Solanum tuberosum L. 'Superior' Colorado potato beetle (CPB); Leptinotarsa decemlineata (Say) Brian A. Nault John Speese III Eastern Shore AREC 33446 Research Drive Virginia Tech Painter, VA 23420 Phone: (757) 414-0724 EVALUATION OF IN-FURROW AND FOLIAR MATERIALS TO CONTROL CPB IN POTATOES, 1998: Potatoes were planted on 1 Apr at the Eastern Shore Agricultural Research and Extension Center near Painter, VA. Each plot consisted of four 20-ft-long rows. Plots were separated across rows by 6 ft and within rows by 5 ft of bare ground. The experiment had 7 treatments plus an untreated check arranged in a RCBD replicated six times. The in-furrow treatments were applied at planting using a propane-pressurized backpack sprayer equipped with a single, hollow cone nozzle boom calibrated to deliver 26 gpa at 40 psi. The foliar treatments were applied on 28 May when the larval threshold of 4 small (1 st and 2nd instars) and 1.5 large (3 rd and 4th instars) CPB larvae was met in untreated plots. Foliar insecticides were applied using the same gallonage, pressure, and sprayer as mentioned above, but the rig was equipped with a 3 hollow cone nozzles/row arrangement. On 28 May, potato leafhoppers, Empoasca fabae, were controlled in all plots receiving foliar treatments plus the untreated check with Dimethoate 4EC at 0.25 lb (AI)/acre. No potato leafhoppers were observed in the in-furrow treatments on 28 May. Data were taken weekly from 25 May through 24 Jun from the center 2 rows of each plot and included the following: number of CPB adults, egg masses, small and large larvae/10 randomly selected stems in each plot, and a visual estimation of percent defoliation within each plot. The center 2 rows of each plot were harvested on 8 Jul and tubers were graded and weighed. The CPB infestation was low and the larval population peak occurred later than usual. On 28 May and 3 Jun, there were no significant differences between the numbers of CPB overwintering adults and egg masses in plots that were treated in-furrow at planting and in those not treated. Before the application of foliar treatments, there were significantly fewer small and large CPB larvae in the in-furrow treated plots than in those not yet treated or in the untreated check. On 3 Jun, there were fewer small CPB larvae in treated plots than in untreated ones, but this difference was not statistically significant. There were significantly fewer large CPB larvae in all treated plots than in the untreated check. Although the number of large larvae in treated plots did not differ significantly among each other, there were considerably more in plots treated with Agri-Mek 0.15EC. On 24 Jun, there were significantly fewer 1st-generation CPB adults (F1) in all treated plots than in the untreated check. However, there were no significant differences in the number of F1 adults among treated plots. On 9 Jun, mean percentage defoliation was significantly lower in all treated plots than in the untreated check, but the level of defoliation was higher in plots that received foliar treatments than in those that were treated in-furrow at planting. On 24 Jun, defoliation levels in all treated plots were lower than in the untreated check, but the level of defoliation did not differ among treated plots. There were significantly more Chef-sized tubers in plots treated in-furrow than in those treated with foliar sprays; there were no Chef-sized tubers in the untreated plots. Total Grade A yield was highest in plots treated in-furrow with either Admire or CGA-293343 followed by plots treated each with a single foliar application of Agri-Mek, CGA-293343, Agenda and Provado. Grade A yield in plots treated with Provado did not differ from yield in the untreated control. This result was likely due to a heavy and prolonged period of potato leafhopper infestation that was not controlled adequately with a single application of Dimethoate.
