Control of annual broadleaf weeds by combinations of herbicides in sugar beet

Sugar beet is a poor competitor to weeds. Weeds are a major constraint to sugar beet productivity. Field experiments were conducted at Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry (55o23′ N, 23o51′ E) during the period 2010–2012 on a loamy Endocalcari-Epihypogleyic Cambisol (CMg-p-w-can) to determine the influence of tank-mixed herbicides phenmedipham + desmedipham + ethofumesate (136.5 + 106.5 + 168 g ha-1 a.i.) with chloridazon (624 g ha-1 a.i.), metamitron (700 g ha-1 a.i.) and triflusulfuron (3.75 g ha-1 a.i.) on broad leaf weeds. Phenmedipham + desmedipham + ethofumesate was applied at three doses, 1/1, 2/3 and 1/2 of the recommended dose. Metamitron was applied at two doses, 1/1 and 1/2 of the recommended dose. All herbicide combinations acted similarly in reducing these weed species: Chenopodium album, Thlaspi arvense, Tripleurospermum perforatum, Polygonum aviculare, Viola arvensis, Veronica arvensis, Lamium purpureum, Capsella bursa-pastoris and Euphorbia helioscopia. The efficacy of phenmedipham + desmedipham + ethofumesate at full (1/1) dose was similar to that applied in a tank mix with chloridazon, metamitron and triflusulfuron at full dose. There were no significant differences in weed weight. Having reduced the dose of phenmedipham + desmedipham + ethofumesate by 33% and 50% in a tank mix, the dry weight of C. album, T. perforatum and P. aviculare increased not significantly. The addition of chloridazon, metamitron and triflusulfuron at full dose had a similar impact on weeds. The action of triflusulfuron was longer because the weight of dominant weeds (C. album and T. perforatum) decreased (6–37%) during all crop growing period. Reducing the dose of metamitron from 525 to 350 g ha-1 a.i. (33%) in a tank mix with phenmedipfam + desmedipham + ethofumesate at 1/2 dose, the dry weight of C. album, T. perforatum, P. aviculare, V. arvensis and C. bursa-pastoris increased not significantly. By reducing the dose of herbicides in a tank mix, the number of active ingredients (a.i.) should be increased.