Impacts of herbicide sequences and vertical tuber distribution on the chemical control of yellow nutsedge (Cyperus esculentus L.)

Cyperus esculentus is an invasive perennial sedge threatening agricultural production. In Belgium, best in-crop control options involve, amongst other methods, growing maize in monoculture which allows the sequential use of selective herbicides with activity against C. esculentus. Two pot experiments were carried out to investigate the effect of genetically different clones and chemical control strategy on C. esculentus control. Additionally, the effect of two vertical tuber distributions (uniform in the 0-26 cm layer or non-uniform with 60% of the tubers in the 6 cm top-layer) was studied. Strategies were based on S-metolachlor, dimethenamid-P, mesotrione, bentazon, pyridate, nicosulfuron, glyphosate, halosulfuron-methyl, foramsulfuron and thiencarbazon-methyl used in mixture and/or sequence and applied at different crop stages. Control efficacy was measured by analysing tuber number, dry tuber biomass and above-ground dry biomass. Tuber number of clones treated by chemical control strategies was up to 100% lower and up to 41% higher relative to the untreated control. Clones showed up to 74% percentage point difference in control of tuber number. In both experiments, strategies with pre-plant incorporated dimethenamid-P followed by two post-emergence applications of mesotrione and pyridate, in 5-6 leaf and 8-9 leaf stage of maize, was most effective and consistent across C. esculentus clones. In general, C. esculentus control was up to 27% better in plots with high proportion of superficially buried mother tubers than in plots with more uniform vertical mother tuber distribution. Hence, the vertical tuber distribution may significantly affect the performance of C. esculentus herbicidal strategies. Overall, chemical control strategies should be complemented with alternative methods (e.g. competitive cropping systems and non-inversion tillage) to achieve satisfactory control.