Cultivar and planting date effects on soybean stand, yield, and Phomopsis sp seed infection

Experiments were conducted in a field near Portageville, MO, from 1992 to 1994 to determine cultivar and planting date effects on soybean stand, yield, and seed infection with fungi. Soybean cultivars Asgrow 3733 (maturity group III), Ring Around 452 (maturity group IV), Hutcheson (maturity group V), and Asgrow 6785 (maturity, group VI) were each planted in 75-cm-wide rows in tilled soil. The planting dates were mid-April, mid-May and mid-June. In 1992, stands of Hutcheson and Asgrow 6785 were greater than stands of Asgrow 3733 and Ring Around 452 for mid-April plantings. Stands were similar among all cultivars and planting dates in 1993 and 1994. Yields of Hutcheson and Asgrow 6785 were similar for all planting dates and were greater than yields of Asgrow 3733 for all planting dates. Yields of Hutcheson and Asgrow 6785 were greater than those of Ring Around 452 for mid-April and mid-May plantings. The percentage of seed infected with Phomopsis sp. was greater in Asgrow 3733 than for the other cultivars in mid-April and mid-May plantings. The percentage of seed infected with Phomopsis sp. was low in Asgrow 6785 each year and was similar for all planting dates. Low yields and problems of seed infection with Phomopsis must be resolved for early planting of Asgrow 3733 to be a practical production system in the upper mid-south. Mid-April planting of Hutcheson and Asgrow 6785 may be a practical cropping system for the upper midsouth because yields, stands, and seed infection with Phomopsis sp. were similar to those of mid-May plantings and harvest was earlier.