EFFECTS OF GRAIN-SORGHUM (SORGHUM-BICOLOR) HERBICIDES ON CHARCOAL ROTFUNGUS

Laboratory and greenhouse studies examined effects of atrazine, alachl or, and metolachlor on growth and colonization of grain sorghum roots by Macrophomina phaseolina, causal fungus for charcoal rot disease. In laboratory studies, all three herbicides reduced fungal colony diamet er and increased production of microsclerotia. Alachlor and metolachlo r reduced germination of fungal microsclerotia. Atrazine did not affec t microsclerotia germination, but lessened the effects of alachlor and metolachlor on germination when applied in combination. In greenhouse studies, atrazine reduced numbers of M. phaseolina microsclerotia rec overed from soil after 8 wk, and this resulted in reduced colonization of roots by this fungus at harvest. Colonization of grain sorghum roo ts by M. phaseolina was not affected by alachlor or metolachlor. Grain sorghum growth was reduced by atrazine at all intervals and by alachl or and metolachlor at harvest, despite use of seed safened with cyomet rinil.