Tolerance of Sorghum bicolor (L.) Moench to Several Herbicides1

Abstract We evaluated 40 varieties of Sorghum bicolor (L.) Moench representing 27 diverse subclassification groups for tolerance to herbicides. Sorghums studied included commercial varieties from the continental United States and cultivars which have not reached the temperate zone. These sorghums were developed or originated in the USA, India, China and seven African countries. Clay soil and sand were treated with 3.2, 9.6 and 28.8 ppm of 2‐chloro‐4,6‐bis(isopropylamino,‐s‐triazine (propazine), 3‐(hexahydro‐4,7‐methanoindan‐5‐yl)‐lmethylurea (norea), 2‐tert butylamino‐4‐ethylamino‐6‐methylthio‐s‐triazine (GS‐14260), 3‐(3,4‐dichlorophenyl)‐I‐methoxy‐l‐methylurea (linuron) and 2‐chloro‐N‐isopropylacetanilide (propachlor). Herbicides differed significantly in the amount of injury caused to sorghum. The following relationships were found in order of increasing damage: propachlor, 10.5%; propazine, 35.7%; norea, 50.0%; GS‐14260, 59.5%; and linuron, 72.4%. Sorghum varieties which produced well in untreated herbicide media also produced best in herbicide‐treated media. Varieties ‘IS 7363’ and ‘PI 285042’ were consistently most tolerant regardless of herbicide. Varieties that ranked in the top 12.5% of the control were not killed by the various herbicides unless all varieties were destroyed. Response to herbicides does not appear to be inherited simply, although differences in tolerance do exist. Dry weight frequency distributions for response to each herbicide indicate near normal curves. Tolerance to herbicides was most evident in the caudatum, durra, and conspicuum groups. Herbicide tolerance was more pronounced in sorghums from equatorial Africa than from the areas where varieties have been developed through intensive breeding programs.