Efficacy of Foliar and Soil-Applied Materials for Lepidoptera Control in Tobacco, 2017

The efficacy of several foliar insecticides and a soil-applied insecticide against lepidopteran pests of tobacco was assessed at two locations, the Lower Coastal Plain Research Station (LCPRS) in Kinston, NC and the Upper Coastal Plain Research Station (UCPRS) in Rocky Mount, NC. At each location, 10 treatments, including an untreated check, were arranged in a randomized complete block (RCB) design with four replicates per treatment (Tables 1 and 2). At both locations, plants for all treatments, except the Verimark treatment, were treated in the greenhouse with Admire Pro® 4.6F (Bayer Crop Sciences) at a rate of 0.6 fl oz/1000 plants 1–3 days prior to transplanting to control aphids and flea beetles. Verimark treatments were applied to trays immediately before transplant at UCPRS and applied 3 days before transplant at LCPRS. For all greenhouse tray treatments, the materials were applied using a CO₂-pressurized sprayer fitted with a single-nozzle boom affixed with a flatfan nozzle in a spray volume of 1 liter of water per four trays, and treatments were washed into the soil media using twice the application volume of plain water. If not treated immediately before transplant, Verimark- and Admire-treated plants were kept in separate float beds to prevent cross-contamination. Plots at UCPRS were planted on 21 Apr, and at LCPRS 8 May. Each 0.018 acre plot consisted of four, ca. 25 plant, rows. Insect counts were made in the center two rows of all plots starting 3 wk after transplant (WAT) and continued until 14 days after the late season hornworm application. Plots were observed weekly for caterpillar infestation, and egg hatch, with threshold treatments applied based on these observations. Foliar treatments were applied via a CO₂-pressurized backpack sprayer at 52 psi in a spray volume of 15 gpa for budworms and 30 gpa for hornworms. HaNPV treatments were applied at egg hatch, at economic threshold, or at both egg hatch and threshold. All other foliar treatments were applied when insects exceeded the current economic thresholds (10% of plants infested with at least one budworm or one hornworm per 10 plants). Tobacco budworms (TBW) reached threshold once pretopping at UCPRS. The HaNPV Egg Hatch treatments were applied on 9 Jun, and threshold-based treatments were applied on 15 Jun. HaNPV Egg Hatch treatments were also applied on 13 July for hornworms (HW), and all foliar threshold treatments were applied on 17 July. At LCPRS, budworm oviposition was not observed until the week that the caterpillar infestations also exceeded the economic threshold, so all treatment were applied on 8 Jun. This was the only application targeting tobacco budworm at this location. Rain delayed treatment until 2 days after pretreatment count. Against hornworms, HaNPV Egg Hatch treatments were applied on 10 July, and all foliar threshold treatments were applied on 20 July. Data were analyzed in SAS v. 9.4 via proc mixed with treatment, date, and treatment × date interactions as fixed effects and replicate nested in treatment as a random effect. If significant treatment × date interactions occurred, means were compared within each date. Means were separated by Fisher’s protected LSD (α = 0.05). No phytotoxicity was observed in any plots following application.

Budworm numbers in Verimark-treated plots at LCPRS were significantly lower than in all other untreated plots at on 5 Jun, 31 days after treatment (DAT). However, this effect did not persist past this date. Verimark-treated plots at UCPRS did not have budworm counts that differed from the untreated check. Although hornworm numbers were above the economic threshold, Verimark-treated plots showed significantly lower hornworm numbers than the untreated check plots at both stations for at least one date (Tables 2 and 3). This effect was stronger and more prolonged at UCPRS (Table 2). Foliar applications of Steward, Coragen, Blackhawk, and Belt all significantly reduced budworm numbers below the untreated check and most treatments were close to or below the current economic threshold for 2 to 3 wk after application (Tables 1 and 4). These materials similarly reduced hornworm numbers below the untreated check and well below the economic threshold within 4 DAT (Tables 2 and 3). Steward treatments had at least 1 wk shorter residual effects against budworms than the other foliar treatments, and higher rates of Steward did not give significantly better control than the lowest rate against either caterpillar type. At UCPRS, HaNPV applied at egg hatch, threshold, or at both egg hatch and threshold did not have significantly different infestation rates of budworms from the untreated check at any point during this period (Table 1). At LCPRS, the egg hatch only application had significantly lower budworms than the check on one date, but populations always exceeded the economic threshold (Table 4). At both stations, the HaNPV threshold treatment had significantly lower hornworms than the untreated check for at least one date. However, this treatment did not lower hornworm populations below the one hornworm/10 plant economic threshold, and severe plant injury still occurred (Tables 2 and 3). This research was supported by industry gifts of product and research funding.