Purpose. To study the features of weed infestation of Miscanthus × giganteus stands and to estimate the level of its productivity at different duration of joint vegetation with weeds.Methods. Field, laboratory.Results. The competitiveness in Miscanthus × giganteus in the first year of vegetation was investigated. The plants of miscanthus form a branched root system, so they feel great on degraded, sandy soils. However, in the first year, miscanthus grows slowly and requires intensive protection from weeds. It was established that in the period from 10 June to 10 July the maximum growth of biomass per unit area was formed by plants of such species as Chenopodium quinoa (151.0 g/m2) and Persicaria maculosa (126.0 g/m2), with variation of the index of increase in mass of 107.4%, which is a very large variation. In the period from 10.07 to 10.08, the maximum intensity of growth was observed in the following species: Echinochloa crus-galli (347.0 g/m2), Amaranthus retroflexus L. (257.0 g/m2), Setaria glauca L. (199.0 g/m2), Chenopodium quinoa (172.0 g/m2), and Persicaria maculosa (172,0 g/m2). The increase in the duration of the period of joint vegetation of crops with weeds until 10 June resulted in formation of weed mass on average up to 331 g/m2 and the average yield of Miscanthus × giganteus of 288.9 g/m2 that was lower by 29% compared to the yield on the control sites, where the plants were vegetated without weed influence. There is a very strong correlation between the accumulation of vegetative mass of weeds and the duration of their combined vegetation with miscanthus: r = 0.94. It is logical from the point of view of changes in the level of productivity of plants and there is a change in the accumulation of vegetative mass of miscanthus depending on the duration of the joint vegetation with weeds. Under these conditions, the equation has a strong inverse correlation relationship: r = -0.86.Conclusions. Under optimal conditions for growing Miscanthus × giganteus in the first year, 1.82 t/ha of dry biomass can be obtained that corresponds to solid biofuel production of 2.00 t/ha and energy output of 33.9 GJ/ha. At the 60-day weediness of crops, the yield of solid biofuels is significantly reduced to 1.43 t/ha, which corresponds to energy yield of 24.3 GJ/ha.