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Postemergence Control of Kochia and Russian Thistle in Early Spring¹

In semiarid regions, soil preparation precedes seasonal spring rains to conserve moisture. However, the early emergence of kochia [Kochia scoparia (L.) Schrad.] and Russian thistle (Salsola kali L. var. tenuifolia Tausch) severely competes with early-seeded crops, such as sugarbeets (Beta vulgaris L.), or requires additional soil tillage prior to planting other crops. Objectives of this study were to evaluate postemergence control of kochia and Russian thistle for potential use in minimum till farming or postemergence control in established sugarbeets. Herbicides, with foliar activity, were applied at various stages of weed development in several field experiments on loam soil (mixed, thermic Paleustalfs and Paleustolls). Herbicidal efficacy was evaluated with regard to vegetative development of the weeds.

Early growth of kochia and Russian thistle was highly diverse in the spring, which would preclude herbicide applications at prescheduled calendar dates before planting crops. Herbicidal control with postemergence applications was best when weeds were small but growing vigorously. Of the herbicides evaluated, only paraquat (1,1'-dimethyl-4,4'-bipyridlnimn ion) at 0.6 kg/ha consistently controlled both species. Complete postemergence control of kochia and Russian thistle was not feasible with diuron [3- (3,4-dichlorophenyl)-1,1-dimethylurea], atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino) -s-tri. azine]; herbicides which might also provide residual weed control in subsequent tolerant crops. In sugarbeets, kochia up to 2.5 cm tall, was effectively controlled with phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate) at 1.1 or 1.7 kg/ha without injury to the crop.

Key Words: No-till • Sugarbeets • Annual weeds

² Formerly Assoc. Prof. and Res. Assoc., respectively, Tex. Agric. Exp. Sm., Lubbock, TX 79401. Now Asst. Director, Tex. Agric. Exp. Sm., College Station, TX 77843. Manager, Field Development, Agric. Division, Rhodia, Inc., New Brunswick, NJ 08903.

³ Professor of Weed Science, Texas Agric. Exp. Stn., Bushland, TX 79012.

Received for publication May 3, 1974.