The effect of mesotrione applied with adjuvants on weed control efficacy and forage sorghum tolerance


Abstract: Field experiments were conducted over 2 years to determine the influence of timing, rate, and method of application of mesotrione on weed control, forage sorghum injury, and fresh weight biomass. Sucrosorgo 506 sorghum was treated with 120 and 80 g ha^{-1} of mesotrione with petroleum oil (PO) or methylated seed oil (MSO) plus 28% N urea-ammonium nitrate liquid fertilizer (UAN). Mesotrione was applied once between the 4- and 6-leaf stages of sorghum or split and applied between the 2- and 3-leaf and the 6- and 7-leaf stages in 2 equal applications, with or without adjuvants. Mesotrione at 120 g ha^{-1} effectively controlled all weed species, except Geranium pusillum. At 80 g ha^{-1} it effectively controlled Chenopodium album, Polygonum convolvulus, and Polygonum aviculare, and at the 80 g ha^{-1} split application (40 + 40 g ha^{-1}) it effectively controlled P. convolvulus and P. aviculare. Both PO and MSO, added to the spray liquid containing mesotrione at 80 g ha^{-1}, made it possible to effectively eliminate weeds; a split application with PO effectively reduced the occurrence of C. album, Brassica napus, Thlaspi arvense, P. convolvulus, and P. aviculare, and application with MSO reduced the occurrence of C. album, P. convolvulus, and P. aviculare. Mesotrione at 120 and 80 g ha^{-1} as a single application and at an 80 g ha^{-1} split application did not cause injury to sorghum plants. The addition of PO or MSO adjuvant to 80 g ha^{-1} of mesotrione applied at a single rate caused slight injury to sorghum plants, which quickly recovered. No injury or slight symptoms were found after a few weeks on sorghum plants treated with a mesotrione at 80 g ha^{-1} split with PO and MSO. The addition of UAN to the spray mixture, apart from mesotrione and PO and MSO, inhibited growth and chlorosis on the leaves. The rate of 80 g of mesotrione with adjuvants is recommended for forage sorghum.

Keywords: Mesotrione, forage sorghum, PO, MSO, UAN, reduced rate

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