Efficacy of Soil-Applied Systemic Insecticides Against Tobacco Pests, 2014 * Open Access

Efficacy of several soil-applied insecticides ( Table 1 ) was tested against key tobacco pests: TFB, TBW, GPA, and tobacco/tomato hornworms (HW). Two identical experiments were conducted at the Upper Coastal Plain Research Station (UCPRS) in Rocky Mount, NC, and the Lower Coastal Plain Research Station (LCPRS) in Kinston, NC. In each experiment, four replicates of the six treatments, including an untreated check, were arranged an RCB design. Each 0.018-acre plot consisted of four, ca. 25 plant, rows. At LCPRS, pre-transplant greenhouse tray drench (GTD) insecticide applications were made on 7 May 2014 in 1 L water using a CO ₂ -pressurized sprayer fitted a single flat-fan nozzle. Twice the application volume was used to wash the material into the root zone immediately following treatment. GTD treatments were applied as above at UCPRS on 28 Apr. The plants were transplanted on 5 May at UCPRS and 8 May at LCPRS, and in-furrow transplant water (TPW) treatments were applied in ca. 160 gal/A of water using four 5-gal mini-tanks affixed to the planter. Plants received no additional insecticide treatments for the remainder of the experiment, and standard fertility, disease, and sucker management practices were followed.

Data were collected from middle two rows of each plot. To investigate potential phytotoxicity due to insecticide treatments, the width of the largest leaf on 10 plants in two rows of each plot were measured three and four weeks after transplant, and plant height was measured six and seven weeks after transplant on 10 plants in two rows. Beginning three weeks after transplant, the number of TFB on ten plants in two rows, and the number of TFB feeding holes on the largest leaf of each of these plants was counted weekly for three weeks. Plants in these rows exhibiting tomato spotted wilt virus (TSWV) symptoms, a disease vectored by tobacco thrips, were counted weekly from three weeks after transplant until nine weeks after transplant. Additionally, the number of TBW infested plants in two rows of each plot was counted weekly from three weeks after transplant until topping. At five weeks after transplant, the number of GPA infested plants (plants with more than 50 GPA on a single upper stalk leaf, including nymphs) and the number of HW in two rows of each plot were also counted. To see if any of the treatments delayed plant maturity, the number of plants flowering in both rows was counted from first bloom until topping. Plants were topped on 15 Jul at LCPRS and 29 Jul at UCPRS. To look for yield differences among the untreated check, Admire, and Verimark treatments, leaves from five plants in two rows of each plot were hand-harvested and weighed before each priming of the field. At LCPRS, “A” stalk positions were hand-harvested on 14 Aug, and “B” and “C” stalk positions were hand-harvested on 10 Sep. At UCPRS, “A” stalk positions were hand-harvested on 18 Aug, “B” on 1 Sep, and “C” and “D” on 19 Sep. All data were analyzed via repeated measures ANOVA (Proc MIXED; SAS v. 9.3.1) with treatment, date, and the treatment x date interaction as independent variables and replicate nested within treatment as a random effect. If a significant (α = 0.05) treatment x date interaction occurred, data for each week were analyzed in separate ANOVAs (Proc MIXED; SAS v. 9.3.1) with treatment as the independent variable and replicate nested within treatment as a random effect. Means were separated by Fisher’s Protected LSD (α = 0.05).

At both locations, leaf widths, plant heights, and proportion flowering were not significantly different between treatments (data not shown). However, there was a trend ( F_5,18  = 2.75, P  = 0.051) toward untreated check plants having fewer flowers than treated plants the week before topping at UCPRS. TFB feeding holes per leaf (FH/L) at UCPRS were significantly lower than the untreated check for all insecticide treatments on all days after treatment (DAT) measured ( Table 1 ). Live flea beetle counts were similar ( Table 1 ), but the FB population was too small to analyze 36 DAT. At LCPRS, live flea beetle populations were consistently low, and the small amount of damage they did (< 1 FH/L for any treatment) was not significantly different between treatments (data not shown). No difference in TSWV incidence between treatments was observed at either station (UCPRS: F_5,18  = 0.24, P  = 0.93; LCPRS: F_5,18  = 1.19, P  = 0.35), and GPA were not abundant enough at either station for analysis. For TBW infestations, significant differences between treatments were observed at both sites but the data were highly variable ( Table 2 and 3 ), and at LCPRS, these differences were only seen 37 and 46 DAT. Hornworm (HW) infestation was not different between treatments at LCPRS ( F_5,18  = 1.24, P  = 0.32). However, at UCPRS, significant differences in non-parasitized HW ( Table 4 ) and parasitized HW ( Table 5 ) infestation rates were observed between treatments. No differences in yield were seen for any priming among the untreated check, Admire, and Verimark treatments (UCPRS: F_2,9  = 2.70, P  = 0.12; LCPRS: F_2,9  = 0.43, P  = 0.66).

Author notes