Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/22/2005
Publication Date: 1/3/2006
Citation: Bruns, H.A., Abbas, H.K. 2006. Planting date effects on bt and non bt corn in the mid south usa. Agronomy Journal. 98:100-106 Interpretive Summary: Improvements in corn hybrids, including enhanced early season cold tolerance and introduction of Bt genes that give insect resistance, require that the optimum time for planting be frequently reexamined. The effect that delayed planting may have on aflatoxin and fumonisin, two cancer causing compounds produced by fungi that can infect corn grain grown in the Mississippi Delta is also not fully understood. We determined that the optimum time for planting corn in the Mississippi Delta is around April 15 to 20, which is similar to the recommendation made from much earlier research. This recommendation is based on grain yields of mid-April plantings being consistently greater than the early May plantings. Some early April plantings yielded the same amount of grain as the mid-April, plantings but none of them yielded more. We also found that mid-season hybrids are a good option for corn growers in the Mississippi Delta, thus increasing the number of hybrids available to them. We found that Bt hybrids generally yielded more grain than the non-Bt hybrids, primarily because they produced more kernels per ear. Bt hybrids also had less fumonisin contamination than the non-Bt hybrids. However, only in 2003 did the Bt hybrids have less aflatoxin contamination. Planting date did not affect aflatoxin levels any year of the experiment. In 2002, the full season hybrids had more aflatoxin contamination than either the mid-season or short-season hybrids; however no such difference was observed in 2003 or 2004. Aflatoxin and fumonisin contamination appears to be influenced more by the environment late in the growing season than by the genetics of the corn.
Technical Abstract: Ideal corn (Zea mays L.) planting dates vary by region and frequently require updating. Two non-GMO corn hybrids and two Bt [Bacillus thuringiensis (Berliner)] hybrids of three maturity ranges, short-season (1180-1270 GDU 10’s), mid-season (1455-1470 GDU 10’s), and full-season (1540-1625 GDU 10’s) were evaluated for yield, yield components, and mycotoxins in 2002, 2003, and 2004 at Stoneville, MS. Plots were planted in a furrow irrigated split-plot of a randomized complete block design replicated 4 times. Whole plots were plantings in early April, mid-April, or May, while sub-plots were hybrids randomly assigned. Experimental units were four 102 cm rows, 9.1 m long. Growing degree units of a 10 C base (GDU 10) at silking and physiological maturity were calculated. Lodging and dropped ears were inconsequential. Yields were greater for mid-April plantings (8.9, 9.1, and 9.2 megagrams per hectare) than May plantings (7.9, 8.1, and 7.4 megagrams per hectare ) in 2002, 2003, and 2004 respectively but not early April plantings in 2002 and 2004 (8.7 and 9.5 megagrams per hectare respectively). Short season hybrids generally yielded less than mid-season or full season hybrids. The Bt hybrids yielded more than non-GMO hybrids (9.4, 9.0, and 9.0 megagrams per hectare vs. 7.7, 7.6, and 8.5 megagrams per hectare in 2002, 2003, and 2004 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 milligrams per megagram), and much less (28.8 and 7.4 milligrams per megagram) in 2003 and 2004 respectively. The Bt hybrids had less fumonisin contamination than non-GMO hybrids (5.2 vs. 8.5 milligrams per kilogram) but had less aflatoxin only in 2003 (12.4 vs. 45.3 milligrams per megagram).