Efficacy of Insecticidal Seed Treatments and Bifenthrin In-Furrow for Annual White Grub, 2016

Root-feeding white grubs are occasional pests 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 hybrid was planted at a rate of 32,000 seeds/acre with 36 inch rows on 18 Apr 2016 using a Seed Research Equipment Solution planter at Elizabeth City, NC in Pasquotank County. A randomized complete block design was used, which consisted of seven treatments (nine insecticide treatments with one non-insecticide-treated check), replicated four times. Rebounder seed covers, in combination with the Y-Not attachment (Shaffert Mfg. Co. Inc., Indianola, NE), were attached to the planter to administer the Capture LFR to the sidewall of the furrow at 5 GPA. All treatments contained a base fungicide seed treatment. Plots were four rows wide (36 inch rows) by 40 feet long. Stand counts, damage 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 was 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 data at 21 DAP were transformed, using the natural log, to satisfy assumptions of the model. Back transformed means are reported.

At 21DAP, only Poncho and Cyazypyr resulted in significantly greater plant density compared with the untreated check (P = 0.0483). No significant differences among treatments were observed for plant density at 28 DAP (P = 0.051). There were no significant differences among treatments for numbers of injured plants per 80 row-feet at 21 DAP (P = 0.0576). At 28 DAP only Capture LFR, Cruiser plus Lumivia plus Capture LFR, and Poncho significantly reduced numbers of injured plants compared with the untreated check at 28 DAP (P = 0.0027). No significant differences among treatments were observed for vigor ratings at 21 DAP (P = 0.0831). At 28 DAP, Cruiser plus Lumivia plus Capture LFR and Poncho resulted in significantly more vigor than the untreated check (P = 0.0144). Only Poncho resulted in significantly higher yield compared to the untreated check (P = 0.0478). This research was supported by industry gift(s) of pesticide and/or research funding.