Performance of Selected Bt Corn Hybrids/Technologies Against Corn Earworm 2, 2021

Corn hybrids expressing Bt proteins are commonly planted for 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 21 May 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 a RCB design. The non-Bt corn hybrids Dekalb DKC6770 and Pioneer P1870R were included as comparisons. Efficacy of Bt hybrids/technologies against corn earworm was determined by examining 10 ears per plot on 21 Jul during the R3 growth stage for presence of larvae and damage. Corn earworm larvae were categorized as small (first and second instar), medium (third and fourth instar), or large (fifth and sixth 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 3 Aug 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 13 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.

Plots planted to Pioneer P2089VYHR (Optimum Leptra) or Dekalb DKC6599 (Trecepta) had fewer small and medium larvae compared to plots planted to any of the other hybrids/technologies (Table 1). Also plots planted to Dekalb DKC6772 (VT Double Pro) or P1870YHR (Optimum Intrasect) had fewer medium larvae than plots planted to Dekalb DKC6770 (non-Bt). Plots planted to Dekalb DKC6672 (VT Double Pro), Dekalb DKC6599 (Trecepta), Pioneer P1870YHR (Optimum Intrasect), or Pioneer P2089VYHR (Optimum Leptra) had fewer large larvae compared to plots planted to either of the non-Bt hybrids (Dekalb DKC6770 or Pioneer P170R). Plots planted to Pioneer 2089VYHR (Optimum Leptra) or Dekalb DKC6599 (Trecepta) had fewer total corn earworm larvae than plots planted to any of the other hybrids/technologies. Also plots planted to Pioneer 2089VYHR (Optimum Leptra) or Dekalb DKC6599 (Trecepta) had a lower percentage of damaged ears than plots planted to any of the other hybrids/technologies. Dekalb DKC6599 (Trecepta) and Pioneer P2089VYHR (Optimum Leptra) had fewer damaged kernels per ear than that observed in any of the other hybrids (Table 2). No differences in yield were observed among treatments.¹

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