Grain Sorghum (Sorghum bicolor) and Sunflower (Helianthus annuus) Response to MKH 6561 and MON 37500 Residues in Soil1

Field studies in 1998 and 1999 determined the response of grain sorghum and sunflower to soil residues of MKH 6561 and MON 37500 in a failed winter wheat recropping situation. Averaged across years, MON 37500 at 30 g ai/ha reduced sunflower density by 39%. MKH 6561 at 30 or 45 g/ha did not reduce sunflower density, growth, or late-season biomass, whereas MON 37500 reduced late-season biomass in both years. Neither herbicide affected grain sorghum plant density in 1998, but MON 37500 decreased sorghum density 80% in 1999. Sorghum growth, biomass, and yield were limited more severely by MON 37500 in 1999 than in 1998. MKH 6561 had little or no effect on grain sorghum during either year. Differences in crop response to MON 37500 between years was likely because of wheat plant size at the time of application and greater interception and metabolism of the herbicide in 1998 crop year. Nomenclature: MKH 6561, methyl 2-({[(4-methyl-5-oxo-3-propoxy-4,5-dihydro-1H-1,2,4-triazol-1-yl)carbonyl]amino}sulfonyl)benzoate...