No abstract

In the last decade, the prevalence of Atriplex patula as a weed in the Belgian sugar beet area has increased. Possible reasons for its expansion in sugar beet fields, besides a poor implementation of the low-dose phenmedipham/activator/soil-acting herbicide (FAR) system, might be low sensitivity or evolved resistance to one or more herbicides used in sugar beet. Dose-response pot bioassays were conducted in the glasshouse to evaluate the effectiveness of five foliar-applied sugar beet herbicides (metamitron, phenmedipham, desmedipham, ethofumesate and triallate) and three preplant-incorporated herbicides (metamitron, lenacil, dimethenamid-P) for controlling five Belgian A. patula populations. Local metamitron-susceptible and metamitron-resistant populations of Chenopodium album were used as reference populations. Effective dosages and resistance indices were calculated. DNA sequence analysis of the photosystem II psbA gene was performed on putative resistant A. patula populations. Overall, A. patula exhibited large intraspecific variation in herbicide sensitivity. In general, A. patula populations were less susceptible to phenmedipham, desmedipham, ethofumesate and triallate relative to C. album populations. Two A. patula populations bear the leucine-218 to valine mutation on the chloroplast psbA gene conferring low level to high level crossresistance to the photosystem II inhibitors phenmedipham, desmedipham, metamitron and lenacil. In order to avoid insufficient A. patula control and further spread, seedlings should preferentially be treated with FAR mixtures containing higher-than-standard doses of metamitron and phenmedipham/desmedipham and no later than the cotyledon stage.

The aim of this research was to evaluate the potential of mechanical weeding for the cultivation of sugar beet by comparing four weed control programmes (one chemical, two mixed (chemical and mechanical) and one mechanical). Under the dry conditions of 2017, the mixed conditions displayed the best effectiveness (more than 97%), using less herbicide and costing €30/ha less than the chemical scheme, while producing a yield identical to that obtained with fully chemical protection. Conversely, the mechanical programme was ineffective (69%), especially on weeds in the crop row (23% effectiveness only); while its cost was lower (€180/ha), it led to a loss of sugar yield of 18.9% compared to chemical weed control.