MAIZE-DWARF MOSAIC-VIRUS SEVERITY IN CORN WHEN INFECTED JOHNSONGRASS IS CONTROLLED WITH A POSTEMERGENCE HERBICIDE

The impact of either nicosulfuron or primisulfuron on maize dwarf mosaic virus (MDMV-A) severity in corn and corn susceptibility to MDMV-A infection were evaluated in greenhouse and laboratory studies. Neither herbicide influenced severity of MDMV-A in corn or corn susceptibility to the virus. Field experiments at rive sites examined MDMV-A severity in corn as influenced by POST johnsongrass control with either nicosulfuron or primisulfuron applied at the fifth or eighth visible collar stage, no johnsongrass control, or johnsongrass control throughout the season with hoeing. Area under the cumulative virus curve (AUCVC) was reduced when either herbicide was applied at the fifth-leaf stage compared to the eighth-leaf stage, at four sites. Also, AUCVC was reduced when johnsongrass was controlled with a POST herbicide applied at the fifth or eighth collar stage compared to no control, at two sites. Increases in AUCVC were due to a greater number of infected plants rather than more severe MDMV-A infections.