The bacteria from Arthrobacter genus isolated from sugar beet rhizosphere were found to produce gallic, protocatechuic, p-hydroxybenzoic, syryngic, vanillic, veratric acids, p-quinone and two unidentified phenolic compounds. The mixture of the bacterial phenolic compounds increased the phytotoxicity of Roneet, inhibiting the germination of wheat. Model experiments showed that the phenolic acids used with the herbicide Roneet increased its phytotoxicity and p-hydroxybenzoic acid was found to be the most active. It was found that in the presence of the phenolic acids, particularly of p-hydroxybenzoic acid, the herbicide content in the seeds of wheat was reduced. The UV and IR spectra of equimolar amounts of p-hydroxybenzoic acid and Roneet showed the hydrogen bond between H of carboxylic group of acid and O of C=O group of the Roneet molecule. It could be concluded that Roneet conjugated with p-hydroxybenzoic acid was more phytotoxic than the initial compounds.