Corn hybrid response to planting date in the northern corn belt

Growers frequently are concerned about the response of corn (Zea mays L.) t o planting date. Early planting of corn is recommended because full-season hybrids utilize the entire growing season, achieve phyiological maturity be fore a killing frost, and start to dry, thereby increasing profit through r educed drying costs. The objective was to evaluate the influence of plantin g date and hybrid maturity on corn grain yield and han-est moisture in Wisc onsin. Two or three corn hybrids ranging in relative maturity from 80 to 11 5 d were planted between 19 April and 22 June at six locations in Wisconsin from 1991 to 1994. In southern Wisconsin locations, the optimum planting d ate for grain yield of full- and shorter-season hybrids ranged between 1 an d 7 May, and was still at 95% of optimum between 9 and 18 May. In northern Wisconsin, the optimum planting date for grain yield of hybrids ranged betw een 8 and 14 May and was still at 95% of optimum between 15 and 23 May. Gra in yield did not change much when corn was planted between 24 April and 8 M ay. Grain yield of corn planted after 8 May in southern Wisconsin declined at the rate of 0.5 to 1.1% d(-1) over the next 2 wk, accelerating to 1.3 to 1.9% d(-1) and 2.0 to 2.8% d(-1) over the next two 2-wk periods. Grain yie ld of corn planted after 8 May in northern Wisconsin declined at the rate o f 0.2 to 1.7% d(-1) over the next 2 wk. accelerating to 1.7 to 2.2% d(-1) a nd 3.2 to 3.8% d(-1) over the next two 2-wk periods. The decision to begin planting corn early should be based on sob temperature and field conditions . After 20 April, planting of full-season hybrids should proceed as rapidly as field conditions allow. The date to switch from full-season to shorter- season hybrids depends on numerous factors, including corn price and drying costs, but generally occurs by mid-May in southern and by late May in nort hern Wisconsin.