Management of Poa annua on Overseeded Fairways

March 16, 2005

Summary: Studies conducted in 1997/98 indicated that pre-emerge herbicides such as oxadiazon (Ronstar) and prodiamine (Barricade) provided effective control of annual bluegrass -with applications made as late in the year as four weeks prior to overseeding—without damage to ryegrass. However, ryegrass damage did develop if product rates were too high and/or if ryegrass was stressed due to weather conditions, poor irrigation coverage or other factors. In 1998/99, the best performing treatments from the previous year were tested again to confirm results, and to identify optimal rates and timing for oxadiazon. Key results include the following:

• Currently, the commercial standard for poa control on overseeded fairways is ethofumesate (Prograss). Our tests confirmed that when this product is used at the right time, at the right frequency, and at the right rate, long-term poa control at levels reaching 99% can be achieved without any damage to ryegrass. In our tests, 2 post-emerge applications (November and December) of 0.5 gallons Prograss per acre achieved this level of control.
• Good poa control also resulted from a single pre-emerge application of Barricade (1.5 lb/A, 8 weeks before overseeding).
• Moderately good control resulted from Ronstar (100 lb/A, 8 weeks before overseeding) or Barricade (2 applications at 0.75 lb/A: 8 wks before and 8 wks afteroverseeding).
• If pre-emerge herbicides such as Ronstar or Barricade are used, a single application at the full rate before overseeding appears to perform better than split applications divided between one pre- and one post-overseeding application.
• There was no damage to rye or bermudagrass from any of the treatments tested. However, under higher stress conditions (windy and/or dry conditions due to poor irrigation uniformity), we have seen damage to ryegrass with high rates of Ronstar and Barricade.
• In areas where ryegrass is under stress (due to poor irrigation uniformity, disease or other factors), Prograss may be the best option for good poa control, without the threat of phytotoxicity.
• Where stress to ryegrass is not an issue, use of other products, such as Barricade or Ronstar, in alternate years may help avoid development of poa resistance to Prograss.
• If Prograss is applied while bermudagrass is still actively growing, the spring/summer transition back to bermudagrass may be significantly slowed. For this reason, Prograss cannot be applied on a calendar schedule – air temperatures and bermudagrass growth and appearance must be closely monitored to determine the onset of dormancy, and therefore the optimal application timing.

Printable version of full report

Principal Investigators: Wendy Gelernter, Ph.D. and Larry J. Stowell, Ph.D., CPPP, CPAg

Cooperator: Nancy Dickens, Sun City West, Palm Desert, CA

Sponsors: Rhone-Poulenc, Hi-Lo GCSA