The Differential Response of Strains of Wild Carrot to 2,4-D and Related Herbicides

Studies were conducted on the effect of 2,4-D and some related herbicides on a susceptible and a resistant strain of wild carrot (Daucus corota L.). When treated with 2,4-D, 4-(2,4-DB) or 4-(MCPB), plants of the susceptible strain died within a few weeks while those of die resistant strain recovered after showing severe injury symptoms. Treatment with 2,4,5-T or silvex killed both the susceptible and resistant strains.Seeds of the two strains, placed in various concentrations of 2,4-D, showed no differences in germination or radicle growth after 7 days. However, sprays of 2,4-D on seedlings just after emergence produced the differential response. Resistance appeared to develop between germination and the cotyledon stage of growth.There were no differences in the effect of 2,4-D on the respiration of whole tissue of the susceptible and resistant wild carrots.