Optimizing Sulfosulfuron and Sulfosulfuron Plus Metsulfuron-methyl Activity when Tank-Mixed with Vegetable Oil to Control Wild Barley (Hordeum spontaneum Koch.)

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Wild barley has invaded wheat fields ever since flamprop-isopropyl was outdated in Iran. Newly developed herbicides such as sulfosulfuron or sulfosulfuron plus metsulfuron-methyl can control it at higher than recommended dosages, but causing significant wheat injury. Hence, two dose-response experiments were conducted to evaluate their efficacy when tank-mixed with thirteen different vegetable oils, at the Ferdowsi University of Mashhad, Iran, during 2013. Moreover, a wheat cultivar (Gaskogen) was also treated with effective dose of 90% (ED90) of both herbicides (21.44 grams active ingredient (g ai) of sulfosulfuron ha-1 and 41.95 g ai of sulfosulfuron plus metsulfuron-methyl ha-1) with and without each vegetable oil to check selectivity. Averaged over vegetable oils, the effective dose of 50% (ED50) was decreased 2.6- and 3.0-fold with sulfosulfuron and sulfosulfuron plus metsulfuron-methyl, respectively. Among the evaluated vegetable oils, cottonseed and coconut oil were the best ones to enhance the efficacy of both herbicides. The castor oil had the least effect. A negative correlation was observed between the efficiency of vegetable oils and its unsaturated/saturated fatty acids ratio. No phytotoxic effect on wheat was observed when these herbicides were applied with or without the vegetable oils.