The effects of cropping history on grain sorghum yields and anthracnose severity in Arkansas

Sorghum anthracnose, caused by Colletotrichum sublineolum, is found in most grain sorghum producing areas in the U.S.A., including Arkansas. High incidences and severities of anthracnose are infrequent and often limited to portions of some Arkansas fields. However, sporadic epidemics have occurred over many hectares and grain yield losses have been severe on susceptible sorghum hybrids suggesting that better management strategies are needed to improve and maintain high sorghum yields. The objective of this research was to evaluate the effect of previous cropping history on grain sorghum yields and on the severity of sorghum anthracnose in several agricultural environments in Arkansas. Replicated field experiments were conducted in 2005 and 2006 to evaluate sorghum following sorghum, sorghum following maize, sorghum following soybeans, and sorghum following rice on grain yields and anthracnose severity for 30 sorghum hybrids in 2005 and ten hybrids in 2006. The results show that the severity of anthracnose ranged from 0% to >23% and planting sorghum in fields one year after maize, soybeans, or rice appeared to significantly reduce the severity of sorghum anthracnose on most of the sorghum hybrids evaluated in both years. Although anthracnose severity varied across years in these experiments, the data show significant yield increases for most of the sorghum hybrids when sorghum was planted after rice, soybeans or maize, but not when sorghum was planted in the same field in which sorghum was grown in the previous year. Grain yields ranged from 0 kg ha−1 to more than 9500 kg ha−1. These results demonstrate that planting sorghum after sorghum significantly increases anthracnose on most hybrids, that planting sorghum after rice, maize or soybeans can successfully reduce sorghum anthracnose, and that the economic benefits (yields) of these cropping sequences are partially dependent upon the year, the severity of the disease and the hybrid. Other management strategies such as sanitation, elimination of alternative hosts and planting clean, healthy seed or seed treated with an appropriate fungicide, coupled with disease resistance should be helpful and perhaps sufficient to avoid or reduce serious losses from grain sorghum anthracnose.