EN
The objective of this study was to evaluate of the activity of two herbicides – tribenuron methyl and 2,4-D + florasulam applied under various thermal conditions. The evaluation was based on free amino acids (valine, leucine and isoleucine) content in selected weed species and also on fresh weight reduction. Plants of Anthemis arvensis Linnaeus and Galium aparine Linnaeus grew in climatic chambers under two levels of temperature: 25/16°C and 8/2°C. Herbicide were applied at reccomended doses, when weeds were at 2–4 leaf or 1–2 whorls. Amino acids level was recorded using gas chromatography method. Both tested herbicides significantly reduced biomass of weeds, irrespectively of air temperature, although their efficacy was lower in case of application against A. arvensis in low temperature regime. Content of valine, leucine and isoleucine in A. arvensis tissue was reduced after tribenuron methyl application under high temperature conditions. In tissue of G. aparine low level of amino acids after appliaction mixture 2,4-D + florasulam was also observed. Amino acids content in plants, especially in G. aparine, subjected to low temperatures was significantly higher compare to those grown under warmer conditions.