Control of Bitterweed with Herbicides

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Abstract
The herbicide 2,4-D was less effective for bitterweed control when applied at air temperatures < 14.degree. C, compared to applications at 22.degree. C, even when soil water was adequate for active plant growth. There was no difference in bitterweed control whether the ester or amine formulations of 2,4-D were used. At 22.degree. C air temperature, 1.12 kg/ha of 2,4-D + dicamba (3:1), picloram or 2,4,5-T + picloram (1:1) did not improve short-term control (36-182 days) of bitterweed, compared to 2,4-D alone at the same rate. However, at 14.degree. C or when bitterweed were in advanced phenological states (75% with inflorescences), these herbicides provided excellent short-term bitterweed control, whereas 2,4-D was inconsistent. Mixtures of dicamba with 2,4-D slightly improved residual bitterweed control, compared to the same rate of 2,4-D alone. Picloram at 0.56-1.12 kg/ha controlled 60-100% of the bitterweed populations for a year or more following applications in winter or spring. Tebuthiuron at 0.56-1.12 kg/ha was not as effective as 2,4-D at 1.12 kg/ha relative to initial bitterweed control, but provided excellent residual control after 1 yr following winter application.

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