Foliar Treatments for Sugarcane Aphid Control in Grain Sorghum, 2018

This study was conducted to evaluate the efficacy of selected insecticides for control of sugarcane aphid (SCA) on sorghum. The test began when the plots were planted on 18 Apr and was conducted at the Beaumont Center. Four treatments with four replications were arranged in an RCB. Plots consisted of four 30-ft long rows with 30-inch row spacing. Seeds were drill planted at 1 seed/2 inches into League soil (pH 5.5, sand 3.2%, silt 32.4%, clay 64.4%, and organic matter 3.8–4.8%). Plots were fertilized by hand with urea at 38 lb N/acre on 19 Apr and immediately flush irrigated. Thereafter, plots were irrigated or drained as needed. Foliar insecticide treatments were applied on 28 Jun with a 3-nozzle spray boom (800067 nozzles, 50 mesh screens, 27 gpa final spray volume) while sorghum was heading. SCAs were not detected in significant numbers until this time. SCAs were counted on 10 upper and 10 lower leaves from the center rows at specified intervals starting with a pretreatment count on 27 Jun. Seed heads were collected 36 days after treatment (DAT) from center rows and wet weight measured. Data were analyzed by ANOVA and means separated by LSD (P = 0.05).

Pretreatment SCA counts on the upper and lower leaves were similar among treatments (Tables 1 and 2). Pre- and posttreatment counts were typically higher on lower leaves. At 4 and 8 DAT, counts were significantly lower in all treated plots relative to the untreated check on upper and lower leaves. Sivanto 200SL provided the best control on lower leaves. At 12 and 15 DAT, SCA populations had declined on the upper leaves in the untreated plots. On lower leaves starting at 12 DAT, increasing populations of SCA were observed in the Endigo ZCX-treated plots. We do not have an explanation for the increase, but there is prior evidence that pyrethroids can flare aphid populations. The other treatments resulted in lower SCA populations on lower leaves compared with the untreated check. All insecticide treatments significantly increased wet weights of sorghum heads compared with the untreated check (Table 3). Sivanto 200SL provided the best control followed by Centric 40WG and Endigo ZCX, although there were no significant differences in wet weight of heads among insecticide treatments. No phytotoxicity was observed.¹

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