Chemical and cultural control of ground ivy populations: Evidence of a 2,4-D-tolerant biotype and its mechanism of tolerance

Ground ivy (Glechoma hederacea L.) is a stoloniferous, perennial weed that persists in lawn turf. Variable ground ivy response to postemergence broadleaf herbicides is common. A recent survey found that 40% of lawn care service providers encountered ground ivy populations having a variable response to herbicides, and that 79% used 2,4-D either alone or in combination with another herbicide to control ground ivy. With the widespread use of 2,4-D on turf sites, the development of 2,4-D-tolerant ground ivy is a possibility. The objectives of this study were to investigate (1) the response of ground ivy populations to 2,4-D and triclopyr application, (2) 2,4-D absorption and translocation in 2,4-D-tolerant and -susceptible ecotypes, (3) whether differential 2,4-D absorption contributes to 2,4-D tolerance, and (4) nitrogen fertility programming, and preemergence and postemergence herbicide applications for ground ivy control. Ground ivy was sampled from eight U.S. states and one Canadian province. Ground ivy populations showed a highly variable response to foliar 2,4-D application, but less variable response to foliar triclopyr application. NE ground ivy was tolerant of 2,4-D whereas the OH ground ivy was susceptible. The 2,4-D-susceptible OH population absorbed more foliar-applied 14C-2,4-D than the 2,4-D-tolerant NE population. While total translocation of applied 14C was similar for both populations, the OH population translocated slightly more towards the apical meristem of the primary stolon. Neither the addition of a nonionic surfactant to foliar applications of 2,4-D nor exposure of the roots to 2,4-D could negate the variation in response to 2,4-D found between these two populations. Nitrogen fertilizer applications reduced ground ivy encroachment while encouraging high turf density. The preemergence herbicide, isoxaben, limited ground ivy spread. The postemergence herbicides, triclopyr or 2,4-D, when applied at the highest labeled rate, controlled ground ivy acceptably. Ground ivy populations vary in their response to 2,4-D. However, differential foliar absorption of 2,4-D apparently cannot explain this variation. Using the three approaches of proper nitrogen fertility programming, isoxaben application, and 2,4-D or triclopyr application, lawncare service providers could achieve improved ground ivy control