In the transition zone, bermudagrass [Cynodon dactylon (L.) Pers.] is often grown in close proximity to Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.). Inevitably, bermudagrass often becomes an invasive weed in neighboring cool-season grasses. Common bermudagrass is also a naturalized weed that is abundant in this area. Lack of selective herbicides makes it difficult to suppress or control this aggressive perennial weed in cool-season grasses. Field studies were conducted in Blacksburg, VA to evaluate several herbicides for selective bermudagrass control or suppression in Kentucky bluegrass and perennial ryegrass. Our objectives were to determine methods to suppress or selectively control bermudagrass without injuring cool-season turf and to investigate methods to increase effectiveness of mesotrione for bermudagrass control.
Treatments were applied at 280 L/ha and included the following: ethofumesate at 1.68 kg ai/ha, flurprimidol at 0.84 kg ai/ha, ethofumesate + flurprimidol, siduron at 13.44 kg ai/ha, fenoxaprop at 0.04, 0.06, and 0.08 kg ai/ha, fluazifop at 0.04, 0.07, and 0.1 kg ai/ha, mesotrione at 0.28 kg ai/ha, isoxaflutole at 0.28 kg ai/ha, triclopyr at 1.1 kg ai/ha, fenoxaprop at 0.06 kg/ha + ethofumesate, and fenoxaprop at 0.06 kg/ha + flurprimidol. Bermudagrass was green and growing when treated. In Kentucky bluegrass, the two higher rates of fenoxaprop, fenoxaprop + triclopyr, all rates of fluazifop, and isoxaflutole controlled bermudagrass greater than 90% at 18 weeks after initial treatment (WAIT). Ethofumesate + flurprimidol and the two higher rates of fluazifop caused unacceptable injury to Kentucky bluegrass. These studies concluded that mesotrione controlled bermudagrass greater than 80% 18 WAIT without significantly injuring Kentucky blulegrass or perennial ryegrass.
In an attempt to increase efficacy of mesotrione for bermudagrass control, another trial was conducted to determine any possible synergistic effects that carfentrazone and siduron could have on control of bermudagrass with mesotrione. This study compared mesotrione rates (0.11 and 0.22 kg ai/ha), intervals of application (1 and 2 week intervals) over a 6 week period, and tank mixes of potential synergist (none, siduron at 6.72 kg ai/ha, or carfentrazone at 0.03 kg ai/ha). While treatments applied weekly controlled bermudagrass greater than 70%, there was unacceptable injury to Kentucky bluegrass. Tank mixtures with siduron and carfentrazone did improve bermudagrass control by mesotrione. However, as bermudagrass control increased Kentucky bluegrass injury typically increased. Severe injury to Kentucky bluegrass caused a cover reduction of greater than 60% in several cases. Our data suggests that although bermudagrass control can be improved or quickened by mixing siduron or carfentrazone with mesotrione, such mixtures are not viable treatments where Kentucky bluegrass injury is unacceptable.
Willis, J. B., D. B. *Ricker, S. D. Askew, and R. J. Keese. 2005. Bermudagrass control with mesotrione and potential synergists. Proc. Northeast. Weed Sci. Soc. 59:89.