Alternative Control Options for Annual Bluegrass: Response to Zinc

Abstract

Annual bluegrass (Poa annua L.) is the most problematic winter weed that turfgrass managers face in the southeast U.S. Herbicides are often used to control annual bluegrass, however this weed quickly invades most turf areas, and can become the dominant turf species over time. With the existence of both annual and perennial biotypes of annual bluegrass, as well as an increase in herbicide-resistant populations throughout the world, the incorporation of cultural control methods could be vital for controlling annual bluegrass. Objectives of this study were to: 1. determine the tolerance of different cool-season turfgrass seedlings to various zinc (Zn) rates at three soil pH levels, 2. evaluate annual bluegrass control following Zn applications in non-overseeded bermudagrass, and 3. evaluate the effects of Zn on annual bluegrass and bermudagrass in a bermudagrass putting green. The addition of Zn at any rate significantly reduced plant growth of turfgrass species in greenhouse studies. This reduction was observed in plant height, plant dry matter (shoot and root), and germination. Although the effect of soil pH was not as significant as Zn rate, there was a significant increase in plant height as soil pH increased for creeping bentgrass (Agrostis stolonifera L.) and perennial ryegrass (Lolium perenne L.). In field studies, when Zn was applied at a rate of 179 kg ha-1, annual bluegrass populations were significantly reduced. Although lower Zn rates did not provide adequate control of annual bluegrass, there was a linear increase in control as Zn rate increased. Zn reduced clipping yield, increased Zn content in leaf tissue, and increased Zn levels in the thatch layer of the bermudagrass-annual bluegrass putting green community. This research indicates that applications of Zn inhibit germination and significantly reduce the growth of annual bluegrass, as well as other cool-season turfgrasses. Based on this research, when applied in the fall, Zn applications could provide some annual bluegrass control in areas where it is considered a weed. However, further research is needed to better understand the long term effects of Zn applications on bermudagrass and the underlying soil. Additional research should also be conducted to further evaluate various application timings, as well as combining Zn applications with currently labeled herbicides to extend annual bluegrass control.