Insecticide Control of Sugarcane Aphid on Grain Sorghum, 2014

Abstract

Sugarcane aphid is a new invasive pest of sorghum that can cause severe plant injury if not controlled. It first arrived in Georgia in August 2014 and quickly spread across the state. Three insecticide trials were con-ducted to evaluate the efficacy of various insecticides. Trials were con-ducted in Marion County, GA (Trial 1), the Agricultural Expo in Moultrie (Colquitt County), GA (Trial 2), and in a grower field near McDonough (Henry County), GA (Trial 3). Sorghum was planted in early June in 30-or 36-inch rows. Plot size was 4 rows by 20–40-ft long. Treatments in each trial were arranged in a RCB design with four repli-cations. Insecticide treatments were applied at milk/early dough stage. Insecticides in Trials 1 and 2 were applied with a self-propelled high-clearance sprayer with TeeJet 8002 flat-fan nozzles applying 10 GPA at 40 psi on 26 Aug and 5 Sep, respectively. Insecticides in Trial 3 were ap-plied on 25 Sep with a CO 2 -powered backpack type sprayer equipped with TeeJet 8002EVS flat-fan nozzles and calibrated to deliver 15 GPA at 40 psi. No adjuvants were used. SCA were sampled by counting all winged and wingless aphids on five top leaves and five leaves from the middle canopy and calculating the average total number of aphids per leaf. Samples were taken at 0, 2, 7, and 14 DAT in Trials 1 and 3 and at 3, 6, and 14 DAT (no pretreatment sample) in Trial 2. Rainfall totals of 0.65, 1.35, and 3.08 inches occurred during the 14-d period in Trials 1, 2, and 3, respectively. Data were analyzed by sample date with ANOVA and means separated using protected LSD (a ¼ 0.05). Very large numbers of SCA occurred in pretreatment counts in Trials 1 and 3. All rates of Transform 50WG, Sivanto 200SL, and Centric 40WG (Trial 1 only) greatly reduced SCA numbers on all posttreatments days as compared with the untreated check treatments (Tables 1–3). The 1 pt rate of Dimethoate 4E in Trials 1 and 2 reduced SCA numbers at 2–3 and 6–7 DAT as compared with the untreated check, but SCA numbers were not different at 14 DAT. The 1 pt rate of Lorsban 4E did not reduce SCA num-bers in Trial 1 but did reduce SCA numbers at 3 and 6 DAT in Trial 2. The 2 pt rate of Lorsban 4E in Trial 1 reduced SCA num-bers at 2, 7, and 14 DAT as compared to the untreated check and reduced numbers at 2 DAT as compared with the 1 pt rate of Lorsban 4E. A combination of Lorsban 4E and Dimethoate 4E each at 1 pt /acre in Trial 2 also reduced SCA numbers and was statistically similar to the most effective treatments of Transform WG and Sivanto 200SL. The azadirachtin product Ecozin in Trial 3 was not effective against SCA. The pyrethroid insecticide Karate Z also was not effective against SCA in Trials 1 and 2 and had greater aphid numbers than the untreated check at 14 and 6 DAT in Trials 1 and 2, respectively. No phytotoxicity was ob-served with any treatments during these trials. Except for Transform WG and Centric, all products used in these trials are registered for use on sorghum.