Performance of Selected At-Planting Insecticides in Soybean, 2015 *

The impact of selected at-planting insecticides treatments on soybean yield was evaluated at the Delta Research and Extension Center (Washington County). Soybean seed (Asgrow 4934) were planted on a Commerce silty clay loam soil on 22 Apr at a seeding rate of 117,612 seed/acre. Plant emergence date was 1 May. Plot size was four rows (40 in. centers) by 40 ft. Treatments were replicated four times in an RCB. All seed used in the trial received a commercial fungicide seed treatment. The Gaucho treatment was applied as a seed treatment at the commercial rate of 1.6 oz form./cwt of seed. All other insecticide treatments were applied as an in-furrow spray using a CO ₂ spray system attached to the planter. This system was calibrated to deliver 5 gpa through TeeJet 25015 flat fan nozzles (one per row) directed into the open seed furrow and positioned in front of the closing wheels. The impact of at-planting insecticide treatments on soil insect (including southern corn rootworm and wireworms) damage was estimated by determining plant density at 11, 19, and 28 days after emergence (DAE) by counting all plants within a randomly selected 10-row ft section of one of the two center rows of each plot. Pea leaf weevil injury was visually estimated at 13 DAE. At 136 DAE (14 Sep), 25 plants per plot were examined for the presence of Dectes stem borer tunneling, these data were converted into percent damaged plants. Yield was determined by harvesting the center two rows of each plot with a small plot combine on 14 Sep. Yields were adjusted to 13% moisture content and converted to bu/acre. Data were subjected to ANOVA and means separated according to Fisher’s Protected Least Significant Difference.

At 11 DAE, only plots treated with Capture LFR or Verimark (both rates) had significantly higher plant densities compared with the untreated check ( Table 1 ). At 19 DAE, only plots treated with Capture LFR, Gaucho, or Verimark (both rates) has significantly higher plant densities compared with the untreated check. At 28 DAE, only plots treated with Gaucho or Verimark (both rates) had significantly higher plant densities compared with the untreated check. At 13 DAE, only Gaucho, Prevathon plus Acephate, and Verimark (both rates) significantly reduced percent pea leaf weevil damage compared with the untreated check ( Table 2 ). There were no significant differences among treatments for percent Dectes damaged plants. Only Gaucho and Capture LFR resulted in significantly higher yields compared with the untreated check.

Author notes