Mesotrione Provides Postemergence Control of Poa Annua L.

Poa annua L. is the most troublesome weed in intensively managed turfs, and is a world-wide problem for which control strategies are limited. Mesotrione is a relatively new herbicide that controls a broad spectrum of grass and broadleaf weeds in several cool-season turfgrass species including Kentucky bluegrass (Poa pratensis L.). Current recommendations for mesotrione use call for 2-3 applications at a rate of 0.18 kg/ha with 2-3 week intervals between applications. This approach will control many weed species, including creeping bentgrass (Agrostis stolonifera L.), but will not control Poa annua. By applying five applications of mesotrione at rate of 0.11 kg/ha and with an application frequency of twice per week, we have demonstrated that mesotrione can provide a high (>95%) level of Poa annua control in Kentucky bluegrass. The more frequent applications increase the activity of mesotrione, which can cause severe injury to sensitive Kentucky bluegrass varieties.