Dynamics of Changes of Weed Infestation of Field Crops in the Conditions of Ulyanovsk Oblast

The paper is focused on assessing the dynamics of changes in weed infestation of agricultural crops (species and quantitative composition of agrophytocenoses) in the period from 1993 to 2022 based on the data of a continuous phytosanitary survey of the fields of OOO Agro-Invest Plus, Karsunsky raion, Ulyanovsk oblast, with the aim of further developing a system for protecting plants from weed infestation. Data analysis showed that the number of species and abundance of weeds over a 30-year period has decreased, and the structure of the weed component by agrobiological groups and life expectancy has changed. Species spread with organic fertilizers (manure) and resistant to herbicides based on 2,4-D have dropped out of the composition of agrophytocenoses, and more adaptive species have begun to appear instead: cereals—gray setaria, common broom; perennials—tuberous pea, creeping wheatgrass, and, in some fields, common yarrow, field horsetail, etc. The main factors in changing field weed infestation include fluctuations in weather conditions and transformation of the structure of crop areas: reduction of biodiversity in favor of sowing commercial crops (winter wheat, sunflower, and barley), change of agricultural technologies, primarily more intensive soil cultivation, and widespread use of herbicides and mineral fertilizers. Despite the improvement of agricultural technologies, primarily the use of more effective herbicides, the species composition of weeds in agrophytocenoses over 30 years has become more diverse. In 1993, the fields were mainly characterized by the suckering annual and biennial (mono- and dicotyledonous) type of weed infestation, which occupied 92.4% of the surveyed area and suckering rhizomatous annual and biennial (dicotyledonous) occupied 7.6%. In 2022, four complex types of weed infestation were identified: suckering annual and biennial (62.2% of the surveyed area) > rhizomatous annual and biennial (21.9%) > suckering rhizomatous annual and biennial (10.1%) > suckering rhizomatous (5.8%), while fields with very strong infestation of perennial species appeared.