Evaluation of Bt corn products for corn earworm control, 2023 Open Access

The performance of selected Bt corn hybrids and technologies was evaluated for the control of the corn earworm feeding in the ear. The experiment was conducted at the Southwest Research & Education Center near Plains (Sumter County), Georgia. Plots measuring 8 rows (36-in centers) by 40 feet were planted on 24 April 2023. A series of non-Bt and Bt hybrids with various Bt traits were arranged in an RCB with 4 replications. Plots were planted with a 2-row Monoseem planter at the rate of 36,300 seeds per acre and irrigated as needed. All seeds had a seed treatment of clothianidin or thiamethoxam plus fungicides. No post-planting insecticides were applied. Corn earworm larvae were counted on 20 ears per plot on 11 July at growth stage R3. The number of live larvae and exit holes where damage was evident, but larvae had exited the ear were counted as total larvae per ear. Ear damage was sampled as injured kernels and as total area (tip plus kernels) on 20 ears per plot at stage R5 on 31 July. Two rows per plot that were not sampled for earworms or damage were harvested on 7 September with a small plot combined that measured grain weight, test weight, and moisture content. Yields were calculated as bu/acre and adjusted to 15.5% moisture content. All data were analyzed with ANOVA using PROC MIXED with hybrids as a fixed effect and replication as a random effect. When significance occurred, means were separated using Tukey’s HSD test at α = 0.05. Percentage data were received angular transformation for analysis, but nontransformed means are presented.

All the non-Bt hybrids had similar levels of % of infested ears and larvae per ear except for DKC6867 which had fewer larvae per ear than most of the non-Bt hybrids (Table 1). DKC6772 (VT Double PRO) and Pioneer 1366YHR (Optimum Intrasect) had similar levels of infested ears and larvae per ear as most non-Bt hybrids. DKC6604 (SmartStax) had less infested ears and larvae per ear than some non-Bt hybrids. Both hybrids with the Vip3A gene (DKC6606-Trecepta and Pioneer 1366VYHR—Leptra) had no infested ears and larvae per ear at stage R3. Kernel and total damage per ear were variable in non-Bt hybrids. Damage in the VT Double PRO, SmartStax, and Intrasect hybrids was not lower than the range of damage in the non-Bt hybrids. The Trecepta and Leptra hybrids had very little kernel and total damage. Grain yield (Table 1) and grain test weight (data not shown) were not significantly different among hybrids and Bt technologies. Only hybrids expressing the Vip3Aa20 protein (Trecepta and Leptra) had effective levels of corn earworm control.¹

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