Performance of Selected Bt Corn Hybrids/Technologies Against Corn Earworm 1, 2020

Corn hybrids expressing Bt proteins are commonly planted for the management of caterpillar pests, including stalk borers. Many of these proteins also have activity against corn earworm. The performance of selected Bt corn hybrids/technologies against corn earworm was evaluated at the Delta Research and Extension Center (Washington County), Stoneville, MS. Plots were planted on 6 Apr at a seeding rate of 34,000 seed per acre. Plot size was four rows (40 in centers) by 40 ft. Hybrids/Bt technologies were replicated four times in an RCB design. The non-Bt corn hybrids Dekalb DKC6205 and Pioneer P1870R were included as comparisons. Efficacy of Bt hybrids/technologies against corn earworm was determined by examining 20 ears per plot on 29 Jun and 6 Jul during the R3 growth stage for presence of larvae and damage. Corn earworm larvae were categorized as small (1st and 2nd instar), medium (3rd and 4th instar), or large (5th and 6th instar). The number of ears with feeding damage was also recorded. Damage was described as feeding on fertilized and developed kernels. Feeding on unfertilized and/or aborted kernels at the ear tip was excluded. On 27 Jul, at the R5 growth stage, the number of corn earworm damaged kernels was determined on 10 ears per plot. Again feeding on unfertilized and/or aborted kernels at the ear tip was excluded. No evidence of corn borer infestations was observed in this trial. Plots were harvested on 15 Sep when grain moisture was ca. 15%. Larval counts are presented as number of larvae per ear. Number of damaged ears was converted to percent damaged ears. Damaged kernels are presented as number of damaged kernels per ear. Yields were adjusted to 15% moisture content and converted to bu/acre. All data were subjected to ANOVA and means separated according to Fisher’s Protected Least Significant Difference.

At the first sample during R3 growth stage (29 Jun), plots planted to Pioneer P2089VYHR (Optimum Leptra) or Dekalb DKC6599 (Trecepta) had fewer small larvae compared to plots planted to any of the other hybrids/technologies (Table 1). Plots planted to Dekalb DKC6599, Dekalb DKC7027 (VT Double Pro), Pioneer P1870YHR (Optimum Intrasect), or Pioneer P2089VYHR had fewer medium corn earworm per ear than plots planted to Pioneer P1870R (non-Bt) or Dekalb DKC6205 (non-Bt). Dekalb DKC6599 and Pioneer P2089VYHR resulted in fewer medium larvae than Pioneer P1870YHR. Plots planted to Dekalb DKC7027, Dekalb DKC6599, or Pioneer P2089VYHR had fewer large larvae compared to plots planted to either of the non-Bt hybrids or Pioneer P1870YHR. Plots planted to Pioneer 2089VYHR or Dekalb DKC6599 had fewer total corn earworm larvae than plots planted to Dekalb DKC6205, Pioneer P1870R, or Pioneer P1870YHR. All of the hybrids expressing a Bt technology had lower percent damaged ears than the non-Bt hybrids. Also, plots planted to Pioneer P2089VYHR or Dekalb DKC6599 had lower percent damaged ears than plots planted to Dekalb DKC7027 or Pioneer P1870YHR. For the second sample during the R3 growth stage (6 Jul), plots planted to Dekalb DKC6599 had fewer small larvae than plots planted to Dekalb DKC7027, Pioneer P1870R, Pioneer P1870YHR, or Pioneer P2089VYHR (Table 2). Dekalb DKC6599 and Pioneer P2089VYHR resulted in fewer medium larvae than Dekalb DKC6205, Dekalb DKC7027, Pioneer P1870R, or Pioneer P1870YHR. Dekalb DKC6599 and Pioneer P2089VYHR resulted in fewer large larvae than Dekalb DKC6205, Dekalb DKC7027, or Pioneer P1870R. Plots planted to Dekalb DKC6599 or Pioneer P2089VYHR had fewer total larvae and lower percent damaged ears than plots planted to Dekalb DKC6205, Dekalb DKC7027, Pioneer P1870R, or Pioneer P1870YHR. Also, plots planted to Dekalb DKC7027 had lower percent damaged ears than plots planted to Dekalb DKC6205, Pioneer P1870R, or Pioneer P1870YHR. Dekalb DKC6599 and Pioneer P2089VYHR had fewer damaged kernels per ear than that observed in any of the other hybrids, except Pioneer P1870YHR (Table 3). Plots planted to Pioneer P2089VYHR produced more yield than plots planted to Dekalb DKC6205, Dekalb DKC7027, or Dekalb DKC6599. Also, plots planted to Pioneer P1870YHR produced greater yield than plots planted to Dekalb DKC6205 or Dekalb DKC7027.¹

Footnotes