Planting date is critical in maize production because it influences the availability of growing degree days required to mature the maize crop, and the amount of pests on the crop throughout the season. The interactions among maize phenologies, transgenic Bacillus thuringiensis (Berliner) maize(Bt) and seed treatment were studied from 2006 to 2008 based on the following objectives: (1) To evaluate the potential use of planting dates and varying maize maturity in combination with transgenic maize and seed treatment to manage corn rootworm (Diabrotica virgifera virgifera LeConte), (2) To evaluate the potential use of planting dates and varying maize maturity in combination with transgenic maize on oviposition and subsequent larval injury to maize by European corn borer [Ostrinia nubilalis (Hübner)], (3) To evaluate the potential use of planting dates and varying maturity of maize in combination with transgenic hybrids on stalk and ear rots incidence and severity following European corn borer infestation.
Corn rootworm larval feeding was reduced by delayed planting and using transgenic Bt maize and seed treatment. When populations of corn rootworms were high, root lodging occurred on untreated maize and lodging declined in late plantings. Significant yield reduction associated with root injury occurred only in 2007 at Wooster on untreated early planted corn. Increased adult beetles feeding on maize caused silk clipping, resulting in poor seed set and reduced yield. Yield from short season hybrids were comparable to full season hybrids especially in late plantings. The European corn borer study showed higher numbers of egg masses from second generation moths on late planted corn. Injuries on stalks and leaves were significantly higher on non-transgenic corn, and increased with delayed planting. The benefit of Bt maize was more significant when planting was delayed than was early when planting.
Planting Bt hybrids with resistance to European corn borer lowered both stalk rots and ear rots compared with non-Bt genotypes especially on late plantings. Compared with short season hybrids, significant reduction in stalk and ear rots occurred in full season hybrids. In summary, the results suggest that in management of European corn borer and associated diseases (rots), when planting is delayed due to unforeseen circumstances and populations would cause economic damage, planting short season Bt hybrids could be beneficial. For corn rootworms, using a seed treatment or transgenic Bt maize might be beneficial where populations are known to be high and planting is early.