Response of Annual Bluegrass to Zinc in Bermudagrass Turf.

Annual bluegrass (Poa annua L.) is one of the most problematic weeds in turfgrass. Integration of cultural control practices could lead to improved weed control. Initial research showed that zinc (Zn), which is commonly applied as a micronutrient, had a negative effect on annual bluegrass when applied at non-agronomic rates.  Field studies were conducted at the Auburn University Turfgrass Research Unit from 2009-2011. The study was a randomized complete block design with three replicates, conducted on a non-overseeded bermudagrass putting green. Treatments included four zinc rates (22, 45, 90, 179 kg ha^-1), single and multiple applications of fenarimol (2.2 kg ai ha^-1), fenarimol + Zn(22 and 90 kg Zn ha^-1), and prodiamine(1.1 kg ai ha^-1).  Zinc applied at 179 kg ha^-1 controlled annual bluegrass 80% throughout the season. Prodiamine, which is currently not labeled for putting greens, controlled annual bluegrass 90%, while applications of fenarimol controlled annual bluegrass only 40%. These data indicate that by applying 90-179 kg Zn ha^-1, it is possible to greatly reduce annual bluegrass populations. However, the environmental and long-term impact of such Zn applications requires further study.