Evaluation of Near Isoline Smartstax Traited and Refuge Corn Hybrids in Combination With Soil Insecticides at Planting for Larval Corn Rootworm Control, 2016*

Near isoline SmartStax traited and refuge corn hybrids in combination with soil insecticides were evaluated for efficacy against CRW larvae near Clay Center, NE during 2016. During 2015, the trial site was planted to corn (late-planted corn) and pumpkins (insecticide free). The experimental design was a RCB with four replicates, and plot size was 4 rows×70–71 ft length with 30-inch row spacing. The soil type was a Crete silt loam. ‘DeKalb DKC62-77 RIB’ (contains GenSS RIB [SmartStax] insect and herbicide traits) and ‘DeKalb DKC62-78RIB’ (contains GenVT2P RIB [refuge] insect and herbicide traits, but no traits for corn rootworm) (Table 2) corn seed were planted on 24 Apr with a 2-row JD 7100 Maximerge planter with finger pickup seed units. Each corn hybrid received a seed-applied treatment of Poncho 500 (clothianidin at 0.5 mg ai/kernel). A south wind at 10–14 mph occurred at planting. Liquid in-furrow insecticides were applied in 5 GPA water via a compressed air system. Granular in-furrow insecticides were applied via the SmartBox application system. Initial CRW egg hatch was first documented on 2 Jun. Plant populations were evaluated on 14 Jun. The total number of plants per plot was recorded and converted to plants per acre (PPA). Extended leaf height (ELH) (=height from ground to tip of longest leaf extended vertically) of twenty plants per plot was recorded in inches on 16 Jun. Initial adult CRW emergence was witnessed on 27 Jun. The total number of root lodged and dead plants per plot due to larval CRW feeding was recorded on 8 Jul and converted to percentage root lodged and dead plants. No dead plants were observed in trial area and subsequently removed from further analysis. In addition, the total number of broken plants per plot (due to a high wind event on 7 Jul) was recorded on 8 Jul and converted to percentage broken plants. Larval feeding damage was evaluated on 14 Jul. Five randomly selected plants were dug from each plot, washed, and rated using the Iowa State 0-3 scale (0 = no feeding, 1 = one node of roots pruned to within 1.5 inches of the stalk, 2 = two nodes of roots pruned to within 1.5 inches of the stalk, 3 = 3 or more nodes of roots pruned to within 1.5 inches of the stalk). From planting (24 Apr) to larval feeding damage evaluation (14 Jul), rainfall totaled 11.46 inches and overhead irrigation, 3.61 inches. Plots were machine harvested on 12 Oct. Percent moisture and lbs of grain were recorded and corrected to 56 lbs/bu at 15.5% moisture to evaluate yield levels. Data were analyzed by PROC MIXED with mean separation using differences of least square means (P = 0.05).

No significant differences among treatments were observed for plant density (plants per acre) or extended leaf height (Table 1). Mean root injury ratings (Iowa 0-3 Scale) for the untreated GenSS RIB and untreated GENVT2P RIB corn hybrids averaged 0.21 and 1.13, respectively. All of the hybrid – insecticide combinations and the GenSS RIB without an at-planting insecticide resulted in significantly less root injury and root lodging compared to the GenVxerror:OUP_XML_FinalT2P RIB hybrid. The application of Precept 3G to plots planted to the GenSS RIB corn hybrid did not significantly reduce root injury ratings or percentage root lodging compared to plots planted to the GenSS RIB hybrid that did not receive an at-planting insecticide application. Plots planted to the GenSS RIB hybrid (with or without an at-planting insecticide) had a significantly higher percentage of broken plants compared to any of the plots planted to the GenVT2P RIB hybrid. There were no significant differences among treatments for yield.

Author notes