Most weed plants have endurance and high reproductive activity. Weeds on the field are amazing with their vital energy and it's not for nothing that the healers and herbalists turned and pay so much attention to them. They study, make up medical treatment and are used with great benefit in folk medicine. Medicinal preparations from plants based on their biologically active substances have a wide spectrum of action and are of great value in the treatment of many diseases. However, the use of wild-growing raw materials is complicated by the reduction or complete disappearance of populations of valuable medicinal species. Weed plants represent a significant reserve for use in medical practice. As a result of investigations of the Mari scientific research institute of agriculture located on soddy-podzolic soil, the stationary section of the experimental field, the species composition of weed plants in fields of crop rotations with medicinal properties is determined. Weediness of field agrocenoses was determined in the phase of dairy ripeness of cereals and leguminous crops, in the phase of closing the potato tops, at the beginning of flowering of clover and annual grasses. The biomorphological spectrum of weed species indicates that there are 27 species of perennial weeds and 10 species of perennial weeds. The smallest number of weeds in crops was recorded in arid 2010 to 9 pcs/m2, the largest in wet year 2017 – over 400 pcs/m2. Of the 37 weed plants that are found in 21 years of observations, 34 have medicinal properties. However, these plants lead to clogging of agricultural crops and, as a result, to a significant decrease in yield and deterioration in the quality of products.