Evaluation of Insecticides for Control of the Sugarcane Aphid in Grain Sorghum, 2014 *

A study was conducted at the LSU AgCenter Dean Lee Research Station in Alexandria, LA, to evaluate insecticides for management of the SA. Six insecticide treatments, in addition to an untreated check, were assessed in an RCB design with four blocks and one replicate per block. Grain sorghum (Dyna-Gro GX13355) was planted on 5 May on 38-inch centers at a density of 83,100 seeds/acre. Plots were four rows wide and 35 ft long. Insecticides were applied on 1 Jul. A CO ₂ -pressurized bicycle sprayer calibrated to deliver 10 gpa at 40 psi was used with a four-row boom equipped with eight TeeJet TX VS6 nozzles spaced 19 inches apart. Treatment efficacy was evaluated by counting the number of SA on one leaf for three plants on each of the two center rows in each plot. Each leaf was the third or fourth leaf down from the whorl, before the boot stage, or down from the flag leaf, during and after the boot stage. Although sorghum midge, Stenodiplosis sorghicola (Coquillet), populations were below the LSU AgCenter recommended threshold, Karate Z at 1.3 fl oz/acre was applied to the experimental area with commercial equipment on 15 Jul (14 DAT) and 22 Jul (21 DAT) to mimic pyrethroid applications targeting the pest. In addition, Transform at 1 oz/acre and Belt at 4 fl oz/acre were applied to the experimental area with commercial equipment on 29 Jul (28 DAT) to control new SA infestations, as well as headworms, Nola sorghiella (Riley) and Helicoverpa zea (Boddie). The two center rows of each plot were harvested for yield on 9 Sep with a small plot combine. SA counts and sorghum yields were compared using linear mixed models (PROC GLIMMIX, SAS Institute). The SPLICE and SPLICEDIFF options were used to compare SA counts as affected by treatment on each date. Means were separated using Tukey’s HSD ( α  = 0.05).

Pretreatment SA populations attained an average of 480 aphids/leaf on 30 Jun ( Table 1 ). All treatments except Baythroid were associated ( P  < 0.05) with a decrease in SA abundance 3 and 7 DAT ( Table 1 ). Numerical trends suggest that Transform at 1.0 and 1.5 oz/acre provided the fastest and greatest SA control. 14 DAT, numerical trends suggest a lack of SA control in plots treated with Lorsban, whereas plots treated with Transform, Admire Pro, and Leverage 360 only sustained low levels of SA infestations. Effects of insecticides could not be detected 21 and 28 DAT ( P  > 0.05). However, sorghum plants in untreated check, Baythroid-treated, and Lorsban-treated plots had become senescent, thus becoming unsuitable for SA. Transform (1.0 and 1.5 oz/acre) and Admire Pro provided a comparable level of yield protection under conditions where untreated check plots sustained close to 100% yield loss ( Table 1 ).

Author notes