STUDIES ON THE EFFECTS OF METSULFURON METHYL ON THE PARASITISM OF SORGHUM BY STRIGA-HERMONTHICA (DEL) BENTH

Metsulfuron methyl (Ally-Dupont), a sulphonylurea herbicide, was tested at rates of 0.5-2.0 g a.i./ha for the control of Striga hermonthica (Del.) Benth. in two cultivars of sorghum in pot experiments. There was good to excellent Striga control at 1.0-2.0 g a.i./ha applied either pre-emergence or post-emergence to CSH-1 or N-13 sorghum. The herbicide was unacceptably toxic to the Striga-susceptible CSH-1 cultivar when applied pre-emergence, thus eroding any benefits of Striga control. In the Striga-tolerant N-13 cultivar there were considerable increases in the growth of infected plants. The herbicide was better tolerated from post-emergence applications by both cultivars, and CSH-1 plants recovered enough growth from Striga infection to produce grain yields at 1.5 and 2.0 g a.i./ha. Herbicide application at 4 weeks after planting sorghum was less damaging than at 2 weeks. Herbicide safening with 1,8-naphtalic anhydride did not provide any additional benefits with post-emergence application. The efficacy of the pre-emergence herbicide was similar with surface or incorporated application.