Chemical Desiccation of Grain Sorghum1

Desiccation of grain sorghum [Sorghum bicolor (L.) Moench] could benefit seed producers and farmers by permitting earlier combining, maintaining seed viability, and controlling perennial weeds. The rate of sorghum seed drying, seed viability, and plant lodging following desiccation was determined. ‘RS 626’, a widely grown hybrid grain sorghum, was desiccated with glyphosate [N‐(phosphonomethyl)glycine], paraquat (1,1′‐dimethyl‐ 4,4′‐bipyridinium ion), and a 28% N solution at 30 and 25% seed moisture in 1973 and 35% seed moisture in 1974. Six grain sorghum inbred lines desiccated in 1973 gave differential responses. Glyphosate at 2.24 kg/ha and paraquat at 1.12 kg/ha would permit combining (20% seed moisture) 5 to 7 days earlier when desiccated at 30% seed moisture in 1973 and 35% in 1974. However, when desiccated at 25% seed moisture in 1973, only 2 days were gained. Combine yields were reduced due to sorghum lodging following desiccation with glyphosate at 1.12 and 2.24 kg/ha and paraquat at 1.12 kg/ha at 30% seed moisture in 1973. Similar combine losses were experienced on plots receiving glyphosate at 1.12 and 2.24 kg/ha applied at 35% seed moisture in 1974. Data for 1974 showed that germination and emergence percentages of seed from desiccated plots were higher than that from unsprayed plots because an early killing frost reduced seed viability of higher moisture seed from untreated checks. Common milkweed (Asclepias syriaca L.) stands in the succeeding growing season were reduced in one of two experiments with fall applications of glyphosate at 1.12 and 2.24 kg/ha.