The Identification of a 2,4-D Resistant Population of Buckhorn Plantain (Plantago lanceolata) in Managed Turf.

The repeated application of a single herbicide mechanism of action provides selection pressure for the spread of resistant weed species. One such population of buckhorn plantain (Plantago lanceolata L.) was found in central Indiana to have developed a resistance to 2,4-D following 30 years of 2,4-D containing herbicide applications. Specific objectives of this study included (a) quantify the level of the resistance in the buckhorn plantain population to 2,4-D and triclopyr and (b) find alternative chemistries that could be used by the turf manager to control the buckhorn plantain at this location. Greenhouse experiments were conducted to quantify the dose response of a resistant (R) and susceptible (S) biotype of buckhorn plantain to both 2,4-D and triclopyr, two synthetic auxin herbicides from different chemical families. Aboveground measurements of fresh and dry tissue 4 weeks after application (WAA) revealed that the R population was 6.2 to 6.9 times more resistant to 2,4-D than the S population. Following the initial harvest 4WAA, plants were allowed to regrow. Analysis of regrowth data determined that the R population was 30 times more resistant to 2,4-D than the S population. The response of the R and S buckhorn plantain populations to triclopyr rates were similar with both populations being equally controlled by triclopyr. In a field experiment, clopyralid provided ≥ 96% control of the 2,4-D resistant population of buckhorn plantain when applied in October and rated the following June. Phenoxy herbicides 2,4-D; 2,4-DP; MCPP; and MCPA did not control buckhorn plantain in the resistant field plots. This is the first report of 2,4-D resistance in buckhorn plantain, and the resistance mechanism appeared to be limited to within chemical class (phenoxyacetic acid) and not across all synthetic auxin herbicides as the pyridinecarboxylic acid herbicides clopyralid and triclopyr provided control in a field or greenhouse experiment, respectively.