Soybean Planting Date and Maturity Effects on Heterodera glycines and Macrophomina phaseolina in Southeastern Kansas.

Heterodera glycines reproduction and damage potential were evaluated for H. glycines-resistant and -susceptible soybean cultivars from maturity groups (MG) III, IV, and V on two planting dates in each of two years (1990-1991). Infection by H. glycines reduced yields of late-planted susceptible cultivars to a lesser degree than early planted cultivars in 1990 but not in 1991. The MG V susceptible cultivar yielded better than earlier-maturing susceptible cultivars even when yields of resistant cultivars were similar across maturity groups. Soybean yields were a function of nematode densities on roots in 1990, and nematode soil densities and root colonization by the charcoal rot fungus, Macrophomina phaseolina, in 1991. Harvest densities of H. glycines were lower for late-planted than for early-planted susceptible soybeans in 1990; however, nematode population increase was more rapid on roots of late-planted soybeans in 1991. Soybean maturity group did not have a significant effect on nematode populations in either year of the study, but colonization rates of M. phaseolina were lower for MG V cultivars than for earlier-maturing cultivars. Delayed soybean planting and cultivar maturity selection do not appear to be viable management options for H. glycines in southeastern Kansas.