Efficacy of Soil and Foliar Applied Registered and Experimental Materials on Green Peach Aphid and Tobacco Flea Beetle

The efficacy of registered insecticides applied as tray drench, transplant drench and foliar sprays against green peach aphid (GPA) and tobacco flea beetle (TFB) was assessed at the Upper Coastal Plain Research Station (UCPRS) in Rocky Mount, NC. At this location, 12 treatments, including an untreated check, were arranged in an RCB design with four replicates per treatment. On 25 Apr 2019, ca. 25 plants were transplanted into 0.018-acre plots. Each plot was a 4 row (48 in centers) by 50 ft in length plot. Pre-transplant greenhouse tray drench (GTD) insecticide applications were made on 24 Apr 2019 in 1 liter water using a CO₂-pressurized sprayer fitted a single flat-fan nozzle. Two liters of water was used to wash the material into the root zone immediately following treatment. Transplant drench (TD) and foliar treatments were applied to the middle two rows. For TD, two liquid oz of solution was applied directly at the base of each plant using plastic cups. Foliar treatments were applied 2 May 2019 (7 days after transplant) using a CO₂ pressurized backpack sprayer fitted with a single TG2 solid cone nozzle calibrated to apply 15 gal/acre spray volume at 52 psi pressure. TFB holes were counted on the largest leaf of 10 plants in the two middle rows of each plot (20 plants total) beginning 7 days after transplant with a pre-treatment count occurring prior to foliar applications. Additionally, total number of TFB was recorded. Total number of GPA infested plants (≥50 aphids per plant) was determined on the middle two rows of each plot. The number of plants on the center two rows of each plot was used to normalize the GPA counts. TFB and hole counts were analyzed in R v. 3.5.3 using LMER with treatment, date, and treatment × date interactions as fixed effects and replicate as a random effects. TFB and hole counts were square-root transformed to meet assumptions of normality. Proportion GPA infested plants were analyzed using GLMER with treatment, date, and treatment × date as the fixed effects and replicate as the random effect. Proportion GPA infested plants were log(x + 1) transformed. Non-transformed means are presented for clarity. Means were separated by Fisher’s protected LSD (α = 0.05). All data was initially analyzed as repeated measures. If significant effects were found, then within week, differences were investigated by dropping Date and Treatment × Date terms from the fixed effects and independently analyzing each week.

Counts of FB holes revealed a significant effect of Treatment, Date and their interaction. Count of TFB abundance revealed no significant effect of treatment, but did show a significant effect of Date and the Treatment by Date interaction. One week after transplant (2 May) GTD and TD applications resulted in fewer TFB holes than untreated check (Table 1). This pattern continued through 16 May. By 23 May, the Sivanto HL 3.34L GTD and Sivanto HL 3.34L TD treatments did not differ from the untreated check. All foliar treatments resulted in fewer TFB holes than the untreated check at 7 and 14 DAT. Because treatment had no effect on TFB abundance, we did not report those results here.

There was a significant effect of Treatment, Date and a significant interaction between the two for green peach aphid infested plants. Applications of materials as a GTD or TD reduced the proportion of GPA infested plants across all time points compared to the untreated check. Most foliar applications for TFB did not have any carry-over effect for GPA. The Exirel 0.83SC 13.5 fl/oz treatment did reduce the proportion of GPA infested plants on 20 and 27 Jun compared to the untreated check (Table 2). The proportion of plants infested by GPA increased across weeks in plots that received any of the foliar treatments and the untreated check.¹

Footnotes