Changes in transpiration of plants as influenced by herbicides may or may not significantly affect soil water uptake in the field. We compared effects of the relatively new herbicides fluazifop [(±)‐butyl‐2‐(4‐{[5‐(trifuoromethyl)‐2‐pyridinyl]oxy}phenoxy)propanoate], haloxyfop [methyl‐2‐(4‐{[3‐chloro‐5‐(trifluoromethyl)‐2‐pyridinyl]oxy}phenoxy)propanoate], and sethoxydim {2‐[1‐(ethoxyimino)butyl]‐5‐2[2‐(ethylthio)propyl]‐3‐hydroxy‐2‐cyclohexen‐1‐one} applied at various rates to oat (Avena sativa L.) at the 5‐ to 6‐cm stage on transpiration, soil water use, and plant development. In controlled environments, transpiration rates in oat declined about 6 d after herbicide treatment. Time for and the degree of transpiration reduction were herbicide and herbicide‐rate dependent, as were the reductions in plant weight and leaf number. First reductions in soil moisture under laboratory conditions were found 10 d after treatment of oat with fluazifop and haloxyfop and 12 d after treatment with sethoxydim. Similarly, in the field fluazifop treatment required 9 d and haloxyfop and sethoxydim 11 d before significant differences in soil moisture occurred. The correlation coefficient of soil matric potential and dry weight of oat in the field was −0.89 and −0.90, respectively, for 2 yr, 1984 and 1985. Reduction of oat dry matter and soil water use in the field was also herbicide rate dependent.
Two field experiments were conducted in 1984 and 1985 to determine the effects of fluazifop, haloxyfop, and sethoxydim on the suppression of water uptake and competition of wheat to seedling alfalfa. In all cases, suppression of wheat growth and stand led to significant reduction in soil water use. The amounts of conserved soil water significantly correlated with increased numbers of alfalfa plants; the correlation coefficients, respectively, for mid- and late-summer plantings were 0.47 and 0.41 in 1984 and 0.90 and 0.86 in 1985. Conservation of soil water was attributed to growth reduction or cessation of wheat growth by the herbicides and, to some extent, suppression of wheat leaf transpiration. All of the three herbicides would be effective in controlling volunteer wheat in a new alfalfa planting.
The purpose of the research was to determine the effect of several postemergence herbicides on transpiration and growth of seedling oats and wheat. Fluazifop, haloxyfop, and sethoxydim were applied postemergence at various rates to oats and wheat in the 1- to 2-leaf stage in controlled environment rooms and the field. In all cases where transpiration was reduced significantly, oats were affected more than wheat. Generally, haloxyfop and sethoxydim in both controlled environments and the field suppressed oat growth more than wheat. Fluazifop controlled both small grain species equally in the field, but oats were suppressed more under controlled environment conditions. Effects of the three herbicides were always greater in the controlled environments than in the field.
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