Annual Bluegrass (Poa annua L.) Control and Turfgrass Response to Amicarbazone

Abstract

Amicarbazone is a photosystem II (PSII)-inhibiting herbicide being evaluated for annual bluegrass control in bermudagrass (Cynodon spp.) overseeded with perennial ryegrass (Lolium perenne L.). The objectives of this study were to: 1. evaluate the effects of soil versus foliar application of amicarbazone on annual bluegrass, 2. determine cool-season turfgrass response to amicarbazone as affected by temperature, 3. evaluate amicarbazone application timing on annual bluegrass control and perennial ryegrass response in overseeded bermudagrass, 4. evaluate triazine-resistant annual bluegrass populations for potential cross-resistance to amicarbazone, and 5. evaluate field applications of amicarbazone for annual bluegrass control and perennial ryegrass response in overseeded bermudagrass. Annual bluegrass foliage and/or root exposure to amicarbazone reduced annual bluegrass quantum yield (ΦPSII) causing plant death. However, soil exposure was more beneficial for annual bluegrass control. Data from temperature studies suggests as temperatures increased and amicarbazone rate increased, perennial ryegrass and annual bluegrass injury increased. Reduction in ΦPSII of both species suggests PSII of both species was sensitive to amicarbazone regardless of temperature. Amicarbazone application timing studies indicated applications 16 weeks after overseeding (WAO) result in the best combination of perennial ryegrass safety and annual bluegrass control. Amicarbazone/ethofumesate tank-mixes provided similar annual bluegrass control to sequential ethofumesate applications. Amicarbazone applied at 0.53 kg ha-1 in March resulted in the best combination of annual bluegrass control and perennial ryegrass safety; however, these applications were inferior to ethofumesate and sequentially-applied bispyribac. Amicarbazone did not control triazine-resistant annual bluegrass populations in the cross resistance study. Quantum yield data of triazine-susceptible populations suggests amicarbazone efficiently inhibited PSII immediately following treatment. These data suggest triazine-resistant annual bluegrass populations may possess cross-resistance to amicarbazone. This research indicates amicarbazone is a potent PSII inhibitor that potentially provides postemergence annual bluegrass control in bermudagrass overseeded with perennial ryegrass; however, currently registered herbicides may be more efficacious. These studies suggest amicarbazone applications in the spring result in greater annual bluegrass control with greater perennial ryegrass tolerance. Based on this research, factors such as herbicide placement, temperature, and application timing may affect amicarbazone efficacy.