The invasive weed yellow nutsedge (Cyperus esculentus ssp. aurea Ten) leads to important yield and quality losses in arable and vegetable farming in Switzerland. First infestations were reported in the 1990s and the plant has spread in the country since then. To tackle this issue, farmers and agronomists have jointly implemented and evaluated different control methods. We are presenting two research projects aiming to compare and validate different strategies for yellow nutsedge control on infested areas. To this aim, on-farm trials were carried out between 2016 and 2020. In a first project, 14 Swiss farmers implemented different control strategies over a four year period (2016-2019). In a second project the effect of a 3-year fallow (2018-2020), combining repeated soil cultivation with and without application of three different herbicides (S-Metolachlor; Foramsulfuron, Thiencarbazon and Iodosulfuron; Sulfosulfuron), on the nutsedge infestation level was evaluated. To assess the effect of the different control strategies, the number of tubers per litre soil was determined at the beginning of the trial period and at the end of each year. This allowed following the infestation level of each field. Yellow nutsedge was most effectively managed in rotations including late drilled crops, allowing repeated soil cultivation in spring (up to over 90% reduction after 4 years). As an example, repeated soil cultivation in spring, followed by incorporation of Dual Gold (S-metolachlor) and late maize drilling (after May 20th) lead to significant reductions in tuber density. Cultivation of cereals partly reduced tuber numbers or maintained tuber density constant. Furthermore, a key parameter identified for successful control of yellow nutsedge was the determination and motivation of the farmers. Indeed, omitting control measures for several months in an infested field was sufficient to annihilate all previously made efforts. In the fallow trials, applying herbicides did not show any additional effects as compared to repeated soil cultivation only. On average, the reduction in tuber numbers after 3 years of fallow was 75%. To conclude, so far none of the investigated strategies was able to eradicate this weed completely on farm, showing that controlling yellow nutsedge is a very complex, time-consuming and expensive undertaking. In spring 2022, we will start a follow-up project for further optimising the use of a fallow for several years, with the use of different cover crops and without herbicides. We also aim to gain a better understanding on tuber dormancy over time in controlled conditions.
