Southern corn rootworm, Diabrotica undecimpunctata howardi Barber, can cause severe stand loss in reduced tillage corn after a vetch cover crop. Trials conducted over 3 yr found that clothianidin and thiamethoxam neonicotinoid seed treatments and conventional granular insecticides applied in-furrow or as a T-band were very effective against southern corn rootworm. Treatments were categorized as no control (untreated), partial control, and full control based on the extent of seedling injury. In 2 yr, damaged plants were individually marked and their survival, tiller (i.e., secondary stem) production, and ear and grain weight measured. About one-half of plants injured by larvae produced a tiller, with most plants producing tillers within 30 d after planting. All dead-hearted plants not producing a tiller died and were not evident by mid-season. In no control plots with severe damage, healthy plants produced more ears per plant and secondarily more grain weight per plant than healthy plants in full control plots. Plants with early tillers in no control produced ≈38% of the grain weight of healthy plants compared with only ≈6% in full control plots, whereas plants with late tillers in no control plots produced <10% of the grain weight of healthy plants and produced no grain in full control plots. Therefore, in stands with severe seedling damage, remaining healthy plants and damaged plants producing a tiller within 30 d of planting responded to lower plant population by producing more ears and grain per plant. However, in full control plots with low levels of damage, damaged plants producing a tiller often persisted until harvest but produced very little grain thereby acting as weeds with the stand.
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Vol. 106 • No. 4