engleski

Effect of low-rate herbicide treatments on weed biomass and yield of sugar beet

Herbicides are widely used to improve weed control in sugar beet (Beta vulgaris var. saccharifera Aleph.) which is poorly competitive against weeds. Nowadays, mostly due to environmental reasons, herbicides are usually used after sugar beet emergence. Mixture of post-emergence, broad spectrum herbicides have to be applied to control the wide range of weed species in sugar beet crops. Increase awareness of the enviromental damage caused by use of herbicide has aroused grate interest in reducing ther rates as much as possible. One of the way to diminish the herbicide input in sugar beet is to apply reduced herbicide doses at early growth (cotyledon) stage of weeds, when the first seed leaves start to appear. In order to low rates to be effective the first herbicide treatments have to be followed by additional application in relatively short intervals (7-15 days) when each new weed flush appear. This paper reports the results of a two year field study designed to determine the influence of different herbicide rates on fresh weed biomass and yield of sugar beet. All herbicide treatments, except standard (full dose) were used in low rates varying from 1/3 to 2/3 of standard rate and repeated three to five times during vegetation. Tank-mixed herbicide treatments consisted of herbicides desmedipham, phenmedipfam, ethofumesate, herbicidal oil and metamitron. Herbicide quizalofop-p was added to control annual grasses in all treatments. To improve Ambrosia artemisiifolia control herbicide clopyralid was added in some treatments. Treatments 1 and 2 were determined by the growth stage of the first emerged weeds and applied 23 days after sowing date in the first year of research and 30 days in the second year when sugar beet was in cotyledon stage. Treatment three was applied at stage of first true leaves of sugar beet with rates reduced by 1/3, and standard treatment (treat. 4) when sugar beet was at 4 leaves stages with full doses. Sprayings were applied at a water volume equivalent to 200 l/ha. Treatments were replicated four times in a randomised complete block design. Plots were 3, 3 m long with 10 rows of sugar beet (15 m2). Weed control was expressed as percent reduction in fresh weed biomass compared to the untreated control. Measuring was done in July when the weeds were in maximum growth stage. Sugar beet was hand harvested from the central six rows in each plot in October each year. The data were anylsed with ANOVA and LSD test. In both years there were similar weed density. The main weeds present in order of average density per m2 for both years were Echinochloa crus-galli (20), Solanum nigrum (10), Ambrosia artemisiifolia (7), Chenopodim album (6) and Ch. polyspermum (6). Compared with herbicide treatments significantly more fresh weed biomass (85%) and the lowest crop yield (93 %), in both years, occured on untreated check. All treatments gave acceptable weed control which ranged from 80-95 % reduction in weed flora. There was no significant difference in fresh weed biomass between herbicide treatments. Crop yield was not significantly different between herbicide treatments. Although there was no statistical difference between herbicide treatments the best average weed control (95 %) and the gratest average sugar beet yield (57 t/ha) were obtainted where herbicide combination desmedipham, phenmedipfam, ethofumesate, herbicide oil, and clopyralid were applied with residual metamitron reduced by half (treat. 2) compare with standard (full doses) treatment. Increasing the herbicide dose did not obtained better results in weed control and crop yield. This clearly indicate the financially benefit of weed control when appling repeated below-labeled herbicides rates after sugar beet emergence. This approuch should have particular positive effect on enviroment, although it was not the aim of our research.

sugar beet; weed; reduced rates; herbicide

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