Planting date effects on Bt and non-Bt corn in the Mid-South USA

Corn (Zea mays L.) planting dates are regional and vary across the contiguous USA. Improved technologies allow corn to be planted earlier. The objective of this research was to evaluate the effects of planting date on the agronomics of Bt and non-Bt hybrids grown in the Mid-South. Twelve hybrids, two Bt [Bacillus thuringiensis (Berliner)], and two non-Bt for three maturity groups [short-season (1180-1270 GDU 10's), mid-season (1445-1470 GDU 10's), and full-season (15401625 GDU 10's)] were evaluated for GDU 10's at silking and physiological maturity, yield, yield components, and mycotoxins in 2002, 2003, and 2004 at Stoneville, MS. Plots were planted in a split-plot of a randomized complete block replicated four times and furrow irrigated. Whole plots were plantings in early April, late April, or mid-May, while subplots were hybrids randomly assigned. Experimental units were four 102-cm rows, 9.1 in long. Lodging and dropped ears were incon- sequential. Yields were greater for both April plantings (8.6 and 9.2 Mg ha(-1) for early April and late April, respectively) than mid-May plantings (7.8 Mg ha(-1)). Short-season hybrids generally yielded less than mid-season or full-season hybrids. The Bt hybrids yielded more than non-Bt hybrids (9.1 Mg ha(-1) vs. 7.9 Mg ha(-1), respectively). Yields correlated with GDU 10's at silking [yield = 0.037x - 20.416 (r = 0.77)] but not physiological maturity. Aflatoxin was high in 2002 (224.0 mg Mg-1), and much less (28.8 and 7.4 ing Mg-1) in 2003 and 2004, respectively. The Bt hybrids had less fumonisin contamination than non-Bt hybrids (5.2 mg kg(-1) vs. 8.5 mg kg(-1)) but less aflatoxin only in 2003 (12.4 ing Mg-1 vs. 45.3 mg Mg-1).