The Effect of Johnsongrass (Sorghum halepense) Control Method on the Incidence and Severity of Virus Diseases in Glyphosate-Tolerant Corn (Zea mays)1

Abstract

Field experiments were conducted in 2000 and 2001 in Virginia to evaluate the incidence and severity of maize chlorotic dwarf virus and maize dwarf mosaic virus in response to postemergence (POST) johnsongrass control in two corn hybrids. Previous research demonstrated the increased disease severity in virus-susceptible corn hybrids as an indirect effect of POST johnsongrass control. The increased disease severity resulted from greater transmission by insect vectors, which moved from dying johnsongrass to the crop. Recent observations have indicated a lack of virus tolerance in glyphosate-tolerant corn hybrids commercially available in Virginia. A transgenic glyphosate-tolerant hybrid and a nontransgenic virus-tolerant hybrid, similar in growth characteristics and maturity, were subjected to POST treatments of nicosulfuron, whereas the glyphosate-tolerant hybrid was also treated with glyphosate. Both nicosulfuron and glyphosate, broadcast or directed, provided essentially complete johnsongrass control, al...