Efficacy of a New Insecticidal Seed Treatment, Cyantraniliprole for Annual White Grub, 2016

Root-feeding white grubs are an occasional pest of corn in the Southeastern United States and can be very damaging when environmental conditions are conducive to their feeding. The species complex in the Southeastern United States consists of species such as Japanese beetle, Popillia japonica (Newman), green june beetles Cotinis nitida (L.), and annual white grubs Cyclocephala spp. (Coleoptera: Scarabaeidae). This study focussed on the white grub complex. An unknown corn seed was planted on 18 Apr 2016 in Elizabeth City, NC in Pasquotank County using a Seed Research Equipment Solutions planter at a rate of 32,000 seed per acre. A randomized complete block design was used, which consisted of eight insecticidal seed treatments with one noninsecticide-treated check, replicated four times. All treatments contained a base fungicide seed treatment. Plots were four rows wide (36 inch rows) by 40 feet long. Stand counts, injury counts, and vigor ratings were recorded from the two middle rows of each plot approximately 21 and 28 d after planting (DAP). Vigor ratings were based on a 1–9 scale, where the untreated check plots were graded at a 5 and all others were either worse (1–4) or better (6–9) than the check plot. Plants were dug from either of the outer two rows from untreated checks and grubs were taken back to the lab for species confirmation. The genus of pest present was Cyclocephala. The two middle rows of each plot were harvested mechanically on 12 Sep 2016 and corn seed yields were corrected to 15.5% moisture. Data were analyzed using individual mixed model analyses of variance (SAS PROC MIXED), with treatment as the fixed effect and block and treatment × block as random effects. Means were separated using Fisher’s protected LSD procedure and considered significant if P < 0.05. Injury at 21 DAP was transformed using the natural log and injury at 28 DAP was transformed using the square root to satisfy assumptions of the model.

No significant differences among treatments were observed for stand counts at either 21 (P = 0.35) or 28 (P = 0.29) (DAP). Also, there were no significant differences among treatments for numbers of injured plants per 80 row-foot at 21 DAP (P = 0.05). At 28 DAP, all of the insecticide treatments, except Lumivia (0.50 mg A.I./seed), significantly reduced the number of injured plants compared with the untreated check (P < 0.05). At 21 DAP, only cyantraniliprole (all rates) and Poncho VOTiVO plus Poncho resulted in significantly higher vigor ratings than the untreated check. There were no significant differences among treatments for vigor at 28 DAP (P = 0.13). There were no significant differences among treatments observed for yield (P = 0.49). This research was supported by industry gift(s) of pesticide and/or research funding.