Efficacy of Organically Acceptable Materials Against Tobacco Pests, 2016

Green peach aphids, tobacco budworms, and hornworms (HW) are the most common pests in organic tobacco in North Carolina. Although many products are labeled for use on organic tobacco, reliable information about their relative efficacy in this system is lacking. In addition, Entrust is widely used in other organic systems, but not currently labeled for use in tobacco. We conducted field experiments to test the efficacy of six foliar insecticides against green peach aphids, tobacco budworms, and tomato and tobacco hornworms (listed in Table 1). Two 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. At LCPRS, the Pyganic treatment was not included. In each experiment, four replicates of the six to seven treatments, including an untreated check, were arranged in an RCB design. Each 0.018 acre plot consisted of four, ca. 25 plants, rows. Untreated plants were transplanted on 25 Apr at LCPRS and 27 Apr at UCPRS. In the middle two rows of each plot, the number of plants with GPA present, the number of plants infested with >50 GPA per single upper-stalk leaf, and the number of TBW-infested plants were counted weekly from 4 wk after transplant until the time for topping. The number of hornworms in each of these rows was also counted weekly starting 6 wk after transplant until 2 wk after HW-targeting treatments were applied. Plants were left untopped at LCPRS to preserve the hornworm infestation that occurred the week topping was scheduled and topped 6 Jul at UCPRS. All aphid-targeting treatments (Table 1) were to be applied weekly from first incidence of aphids until within a week of topping. GPA-targeting materials were applied at LCPRS on 9 Jun, 17 Jun, and 20 Jun and at UCPRS on 9 Jun, 13 Jun, and 23 Jun using a CO₂-powered backpack sprayer. All but one GPA-targeting applications were performed with a CO₂-powered backpack sprayer connected to a single boom fitted with a T2 solid-cone nozzle at 57 psi and a 15-gpa spray volume. For the application on 17 Jun at LCPRS, the spray volume was increased to 30 gal/acre to improve coverage.

Tobacco budworm-targeting treatments were applied once, when insects first exceeded the current economic threshold of 10% of plants infested with at least one budworm. These applications were applied on 17 Jun at LCPRS and 23 Jun at UCPRS with the same equipment and spray volume as the GPA-targeting treatments applied at that time. Materials that targeted both GPA and TBW were applied only once on these dates. Hornworm-targeting applications were also applied once, when insects first exceeded the economic threshold of one horworm per 10 plants. Hornworm-targeting treatments were applied with a TG3 solid-cone nozzle at 57 psi with a 30-gpa spray volume on 18 Jul at LCPRS. Since severe flooding damaged plots at UCPRS, hornworm treatments did not occur there. All data, except aphid data from LCPRS, were analyzed via Proc Glimmix in SAS v.9.4 with treatment and date as fixed effects and replicate as a random effect. Depending on which was a better fit for the data, a normal or log-normal distribution was used for the model. The LCPRS aphid data started off with significant differences observed between treatments before any pesticides were applied, so these data were analyzed via Proc Mixed with treatment and date as fixed effects, replicate as a random effect, and initial aphid count as a covariate. For all analyses, if the assumption for homogeneity of variance was not met, a Satterthwaite correction was used to adjust the degrees of freedom. Means were separated by Fisher’s protected LSD (α = 0.05).

At LCPRS, significant differences in aphid infestation occurred among treatments (Table 1), with all treatments except Grandevo showing lower aphid counts than the control. Since there was no treatment x date interaction, means of all post-treatment dates combined are presented. Aphid abundance was not affected by treatment at UCPRS (F_6,81 = 0.49, P = 0.81, data not shown). At UCPRS, budworms were significantly affected by several treatments (Table 1), but only Entrust lowered budworm counts below the economic threshold. Since there was no treatment x date interaction at UCPRS, combined budworm infestation means for 2 wk post-treatment are presented. At LCPRS, budworms were similarly affected by treatments, and again Entrust was the only material that decreased budworm populations below the economic threshold (Table 1). By 5 Jul, budworm populations in all treatments at LCPRS had decreased and significant differences were no longer observed (data not shown). Azera, Entrust, and Dipel were the only treatments that significantly lowered hornworm numbers below the control at 7 and 14 DAT, and Entrust- and Dipel-treated plots were on average below the economic threshold of 1 HW per 10 plants during this 2-wk period (Table 2).

This research was supported by industry gifts of product and funding.