Annual bluegrass (Poa annuaL.) is the most troublesome winter annual grass weed on golf courses. Its low-growth habit and unique ability to thrive in moist conditions and compacted areas make golf courses ideal candidates for invasion. This article focuses on postemergence control in established turfgrasses.

Non-overseeded fairways

Photo 1: Gradually, Poa encroaches into greens from untreated fairways.

A recent three-year study [Postemergent Annual Bluegrass Control in Dormant Nonoverseeded Bermudagrass Turf, HortScience 42(3):670-672] investigated various herbicides and timings for postemergencePoacontrol in dormant bermudagrass fairways. TranXit, Monument, Katana, Finale + Envoy, Finale alone, Kerb, Revolver, Finale + Roundup Pro, Roundup Pro + Reward, and Roundup Pro + Envoy treatments provided best control in April whether they were applied in late December or early February.

Roundup Pro alone provided better control when applied in February compared to December while Princep and Image were better when applied in December compared to February. This might explain why some "failures" have occurred with certain products as timing may make a difference. For example, since Roundup has very short residual activity, applying it as late in the season as feasible (bermudagrass is still dormant) normally works better than applying it earlier.

The opposite would be true for Princep since it works best on smallerPoaplants plus has some soil residual activity.

Overseeded fairways

Much interest has been created on the possibility of using Prograss 1.5EC for postemergencePoacontrol in overseeded ryegrass. The key to success is proper timing.

10-Step Plan for Golf Greens

In the Carolinas, two applications are necessary — the first during the third week in November followed by a sequential application three weeks later. It should not be applied after Jan. 15 asPoacontrol will suffer, and chances of injuring or delaying bermudagrass green-up increases. This is why Prograss should not be used where bermudagrass fails to experience complete dormancy.

Another twist we tried was applying a normal initial pre-emergence herbicide 60 days before overseeding followed by one early December postemergence application of Prograss at 1 pound active ingredient per acre (ai/a). We had excellentPoacontrol through spring of 2006 and good control in 2007.

Finally, bispyribac-sodium (Velocity) allowsPoacontrol when treated just prior to seedhead expression. It typically is applied twice, the first in mid to late February followed by a sequential three weeks later. However, temperatures during and immediately following application largely dictate success. Temperatures during the application window should be 70 degrees Fahrenheit daytime and 50 F nighttime (21 degrees Celsius and 10 C, respectively), which is whenPoais most actively growing. If applied outside this temperature window,Poais not as actively growing, and the herbicide can dissipate before control occurs.

In 2008, a 17.6 SG formulation of Velocity will be introduced. Rates will range for overseeded fairways from 6 ounces per acre (oz/a) — or 420 grams per hectare (g/ha) — for two applications or 12 oz/acre (840 g/ha) for a single application. Use the higher rate if maturePoais present. Short term (about five days) yellowing to the treated ryegrass may follow application.