Tolerance of Sorghum to Postemergence Applications of Atrazine

Grain sorghum (Sorghum bicolor (L.) Moench, var. RS-610) grown under field conditions during 1965 to 1967 on three soils in the High Plains of west Texas, was treated at different stages of plant growth with 2-chloro-4-(ethylamino)-6-(isopropylamino)s-triazine (atrazine). Maximum injury was caused by supplemental sprinkler irrigation. Tolerance of grain sorghum to atrazine increased as height of sorghum plants increased. Treatments on 1 and 3-inch sorghum reduced grain yields significantly, but plants treated when 6 inches or more in height produced yields similar to hand-weeded plots, except on Brownfield loamy sand where yields were reduced even at ½ lb/A. Similar trends were observed in 1966 with a forage sorghum (Lindsey 101F). However, yield reductions occurred only when atrazine was applied at 2 and 4 lb/A to sorghum plants I inch tall. Results show that atrazine can be used effectively and safely for weed control in sorghum grown on fine sandy loam or heavier soils in the southern High Plains, providing the crop is at least 6 inches tall when treated.