An assessment of resistance of two plantain ( Plantago lanceolata ) cultivars to phenoxy herbicides

Plantain (Plantago lanceolata L.) is becoming widely adopted in New Zealand livestock systems due to its productivity, nutritional values and its role in reducing nitrate leaching from grazed pastures. Although sometimes grown alone, plantain is generally used in mixtures with grass and clover species; however, this makes it more difficult to selectively control weeds within these swards using herbicides. There has been some selection for phenoxy herbicide resistance in a cultivar of plantain, Agritonic, in New Zealand. Its level of resistance to MCPB, MCPA, an MCPB/MCPA mix, 2,4-D and 2,4-DB was compared to that of a more susceptible cultivar, Tonic, in dose-response experiments. The results showed that the resistance ranged between 1.3 and 3.5-fold compared to Tonic, and it was only significant for 2,4-D and MCPB/MCPA mix in the first and second experiments, respectively. Among all the tested herbicides, rates of MCPB and the MCPB/MCPA mix that are currently used in clover-based pastures were less damaging to Agritonic plants than the other herbicides tested. However, variability in resistance of the Agritonic plants resulted in some surviving the recommended rates of MCPA, 2,4-DB and 2,4-D, suggesting there is potential to select for higher levels of resistance to phenoxy herbicides.