Herbicidal Effects of Fungicides on Arable Weeds

In the present study, the herbicidal effects of two fungicides with the active ingredients expoxiconazole, fluxapyroxad, pyraclostrobin and fenpropimorph on the two arable weeds Lamium purpureum L. and Chenopodium album L. were investigated. The experiments were conducted in a climate chamber under defined conditions. Sowing pods were prepared and plants at the cotyledon leaf stage were pricked out in test pods. Fungicides were applied at six application rates: 0%, 12.5%, 25%, 50%, 100% and 200% of the maximum registered dose rate in Germany. Seven days after application, the first assessment was conducted, regarding growth stage, quantity of plants and visible plant damage. Fourteen days after application, the second and final assessment was conducted, regarding growth stage, quantity of plants, visible plant damage and the fresh weight of the plants. There were herbicidal effects of the fungicides, which were presumably due to the active ingredient epoxiconazole. Epoxiconazole has effects on enzymes that are dependent on cytochrome P-450 and inhibits sterol biosynthesis and probably gibberellin synthesis. By doing so, these fungicides have similar effects to plant growth regulators. Weed species showed differential sensitivities, contractions and growth inhibition and ED50-values were calculated. Notwithstanding the probably minor relevance of the present results in agricultural practice, some effects on arable weeds might result if fungicides are applied at an early growth stage in the field. In some cases, the crop-weed competition could be shifted to the benefit of the crop. Nevertheless, the results are interesting for the field of weed research and for the assessment of the ecotoxicology of fungicides.