Abstract: To establish the weed thresholds of injury to seedlingless growing of tomatoes a field trial was carried out in the conditions of artificial weed infestation, and variants of particular types of weeds with particular density were tested. The trial recorded weed infestation, growth, development and productivity of tomatoes, content of soil humidity and soil nutrients. It was established that at equal number of weeds per area unit, most nitrogen was consumed by Chenopodium album L. and Solanum nigrum L., phosphorus – Datura stramonium L., and potassium – Solanum nigrum L., Chenopodium album L. and Echinochloa crus-galli L. The strongest tomato competitor for water was Solanum nigrum L., and the weakest – Setaria veridis P.B. The highest injury levels were manifested by Datura stramonium L. and Solanum nigrum L. and the biological threshold of injury levels for these weeds was 1 per m2. Echinochloa crus-galli L., Amaranthus retroflexus L. and Chenopodium album L. had lower injury levels, and the biological threshold of injury for them was 2 per m2. Setaria veridis P.B. manifested the lowest injury level. Its biological threshold was 4 per m2.