The use of information about critical periods of harmfulness of weeds in forecasting weediness and possible crop losses can be considered an element of greening corn production. The purpose of the study is to determine the critical periods of harmfulness of the weed component in crops of corn hybrids of different maturity groups in the forest-steppe zone of the Chechen Republic. The study was conducted during the period 2016-2022. in the forest-steppe zone of the Chechen Republic, against the background of a complex type of weed infestation. With the increase in the number of weeds, their air-dry mass also increased in direct proportion, which confirms the fact of intraspecific and interspecific competition in sowing. The critical period of harmfulness of weeds in corn crops is determined graphically; the main parameter for its determination is the crop yield. The yield of the early ripening corn hybrid Krasnodarsky 291 AMB, free from weeds, is 9.77 t/ha; the yield of the crops weeded throughout the growing season is 5.15 t/ha. The longer the period of joint growth of the weed field and cultural components of the agrocenosis, the higher the harmfulness of the first and the lower the yield of the second. In the conditions of the forest-steppe zone of the Chechen Republic in the agrocenosis of the early ripening corn hybrid Krasnodarsky 291 AMB, the critical period for the harmfulness of weeds is the first 30 days from the moment of emergence; and for the mid-season corn hybrid Zernogradsky 354 MV – 25 days. During the established growing season, corn plants are characterized by weak competitiveness.