Q & A WITH

DR . GRADY MILLER

We have experienced high populations of annual bluegrass on our bermudagrass fields here in Oklahoma the last few years . I would like to use chemical control this year , but I am not sure of my options considering our long , cold winters . What are your thoughts ?

I believe annual bluegrass ( Poa annua ) has to be considered among the top five weeds on athletic fields . It withstands low mowing and cold conditions , and prefers wet , compacted soils . It produces huge numbers of seeds that begin germinating in late summer and may continue to germinate throughout the fall , winter and spring . Although classified as an annual , weed scientists have discovered perennial biotypes . Scientists have also documented annual bluegrass resistance to multiple herbicides .

It is hard to talk about weed control without first mentioning cultural practices . Although cultural practices may not provide adequate weed control , they can still impact weed density and your ability to use specific chemicals for weed control . Manage your cultural practices to grow the thickest , healthiest stand of turfgrass possible . Consider if you must overseed in the fall , as this will have a significant influence on available chemical control options . There are significantly more pre- and post-emergence control programs available for non-overseeded fields .

When overseeding , timing of establishment will come into play when considering your options . For example , commonly used pre-emergence products such as pendimethalin , prodiamine , dithiopyr , and oxadiazon ( granular formulation ) applied in the fall may effectively control annual bluegrass , but they must be applied two to four months before overseeding ( depending on product and rate ); otherwise , the overseeding grass can be heavily damaged . Super early pre-emergence applications may also miss a substantial amount of late-germinating bluegrass .

Post-emergence programs have the same issue in that many annual bluegrass post-emergence products cannot be applied to ryegrass , and some can only be applied to totally dormant bermudagrass . Some products can be applied days to a few weeks before overseeding without any injury to ryegrass , whereas others cannot . For example , in the sulphonyl herbicide family , foramsulfuron , rimsulfuron and sulfosulfuron can be used to control annual bluegrass

close to overseeding , but trifloxysulfuron needs be applied at least three weeks before seeding .

The last chemical control strategy that is often used with non-overseeded fields is the use of non-selective herbicides . In Oklahoma , as with many other areas that grow bermudagrass , total dormancy of the turfgrass is expected . Once the bermudagrass is dormant , non-selective products such as glyphosate , glufosinate or diquat may be used . There are also benefits to mixing products with a different mode of action in the tank to increase activity while also managing to prevent herbicide resistance . Some managers may also mix pre-emergence products in with post-emergence products to get longer-lasting control .

Cold winters , as you suggested , have implications with picking a chemical control program . In the transition zone of the United States , or in regions north of the transition zone that are using bermudagrass , winterkill or winter injury is a reality . For example , the pre-emergence herbicide indaziflam provides very good and long-lasting control of annual bluegrass . However , it has up to a 12-month overseeding or sprigging interval , and a six- to eight-month sodding interval . In an area that experiences winter bermudagrass damage , waiting that long before re-establishing a turfgrass can be a huge issue . Product , application rate and timing , as well as residual activity , must be given strong consideration in your environment .

There are far more products and use-options available than those mentioned in this article . With all the factors , products and scenarios to consider , I encourage you to speak with your state ’ s turfgrass specialist or weed scientists to help you figure out the best plan to use in your situation . This is also another great reason to attend local SFMA meetings and learn more about the experiences of other field managers in your area . SFM

Grady Miller , Ph . D . Professor and Extension Turf Specialist North Carolina State University

Questions ? Send them to Grady Miller at North Carolina State University , Box 7620 , Raleigh , NC 27695-7620 , or e-mail grady _ miller @ ncsu . edu

Or , send your question to Pamela Sherratt at 202 Kottman Hall , 2001 Coffey Road , Columbus , OH 43210 or sherratt . 1 @ osu . edu

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