The harmfulness of weeds in the herbage of perennial grasses in the north-west of the Russian Federation

Abstract

Relevance. In the structure of the acreage of the Northwestern region of the Russian Federation, a large proportion is occupied by perennial grasses, the herbage of which can potentially have severe weeds, and the harmfulness of weeds is high. Despite the current situation, the influence of weeds on the formation of an aboveground mass of grasses remains poorly understood.Methods. The purpose of the study is to assess the harmfulness of weed vegetation in the herbage of perennial grasses of the 1st and 2nd years of use in the north-west of the Russian Federation. The research was carried out in 2010–2018 in the fields of grain-grass-row crop rotation of the Menkovsky branch of the Agrophysical Research Institute located in the Leningrad region, in the structure of long-term experience with the application of mineral fertilizers and plant protection products.Results. Studies have shown that weeds cause significantly more harm (6.3 times) to perennial grasses of the 1st year of use than grasses of the 2nd year. Yield losses from the total value of the raw phytomass of weeds amounted to 15.75 c/ha (5.3%) and 2.51 c/ha (1%), including from 1 g/m2 at the time of mowing 0.150 c/ha (0.05%) and 0.07 c/ha (0.03%). The introduction of high doses of mineral fertilizers and the use of herbicides in the integrated crop protection system of grain-grass-row crop rotation led to a decrease in the harmfulness of weeds. In the perennial herbs of the 2nd year of use, the identified effects were significantly more pronounced than in the herbs of the 1st year. Under the influence of mineral fertilizers, the hazard coefficients decreased by 2.6 and 5.7 times, the protective measures systems — by 1.4 and 4.2 times, and the yield losses of green mass — by 2.6 and 10.7 times, 1.9 and 8.9 times, respectively, on grasses of the 1st and 2nd years of use.