The Truth About Poa Annua: Golf's Most Controversial Grass

By Andrew Gyba, Golf Course Superintendent, Glen Abbey Golf Club

As a golfer, even if the ins and outs of course conditioning are not your primary concern. You have undoubtedly heard the term Poa annua before. Whether playing with a fellow member or watching last week’s PGA Tour event, as golfers we hear it all the time. But what is Poa annua, and how does it affect us.

Poa annua, is the Latin binomial name for Annual Bluegrass or Annual Meadow Grass, depending on where you are in North America. Simply it is a proliferous, omnipresent turf type that is found across North America. There is one undeniable fact when it comes to Poa annua or poa for short. Eventually, it will creep into your golf course, putting greens and you will have to deal with it.

Poa seed in full bloom on hole No.15 green Glen Abbey Golf Club (Oakville, ON)

How does it invade golf courses?

Unlike other turf types, Poa annua is a prolific seed producer and generates seed for the entirety of the growing season as opposed to one or two seed production cycles per year as with other turf types. This means that neighboring fields, golf courses, farms and subdivisions will undoubtedly have Poa annua growing within them waiting for the wind to carry its seeds to a new site all season long, day and night. Sometimes the seeds are carried in on golfer’s shoes, sometimes it comes in a roll of sod or in a bag of seed. Once deposited into the turf canopy, plants grow rapidly from seed and can mature, flower and seed within 6 weeks.

Image credit: GCM Online

What does it look like?

The best time for most people to identify Poa annua is early in spring while greens are still developing their mid-season color. Typically, the bent grasses most greens are constructed from a are little slower to green up in the spring. During this time, you may see little coin size patches of lime green grass. This is the typical appearance of newer Poa infestations. With more established infestations the lime green grass will turn into larger patches and produce a camouflage look on the greens. Poa is most identifiable when it is seeding as it will be the only turf type to do so, producing a cauliflower type appearance to the turf stand.

Cons

1. Poa annua grows rapidly, much faster than bent grass. When greens are mown in the morning, they remain true for anywhere from 4-6 hours. Inevitably as the day progresses the difference in the growth rate between the poa and bent grass becomes more noticeable, and by the afternoon the greens can become bumpy. This is exasperated when the poa is seeding as the seed heads will contribute to bumpier, slower greens speeds.

2. Poa annua is less tolerant to many stresses including heat stress, foot traffic, and drought. Because of this predominantly Poa greens require much more attention and can fair much worse through periods of extreme heat, continued drought, or constant foot traffic.

3. Poa annua has higher water requirements. Firmer greens are faster greens, but too dry Poa greens are dead greens.

4. Poa annua has a lower cold tolerance and is more prone to winter kill.

Pros

1. Poa annua survives better in the shade. Many superintendents will encourage Poa annua in difficult greens sites where increasing sunlight is impossible.

2. Poa annua can produce some of the best putting conditions in the world. Due to its inherent density, fine leaf texture, and resistance to grain development; when it is healthy, not seeding and not under stress; poa greens can be an absolute joy to play on. Some of the best greens in the world are famously constructed from Poa annua, most notably Oakmont, Pebble Beach Golf Links, Muirfield, Shinnecock, Riviera, Torrey Pines and Glen Abbey Golf Club to name a few.

What to do about it?

In Canada, control options are limited when it comes to Poa management. For newer infestations, when the Poa annua plants are small coin sized patches, manual removal is an option. Superintendents will routinely organize ‘Poa picking parties’ with staff and plug out the Poa and typically replace with bent grass. One can imagine how arduous this process could be and inevitably some will be missed.

Chemical control is restricted. Velocity is a product available to Canadian superintendents, however the product is not registered for use on putting greens, only for use on fairways. It is essentially a plant hormone that is sprayed on the entire playing surface. The Poa annua cannot process the excess hormone load when the bent grass can. Slowly the Poa should die out. The trouble with this method is that constant, repeat applications are necessary. The product can severely damage your rough surrounds as they are predominately seeded to various types of bluegrasses which Poa annua is a type of, and the formulation can severely weaken your bent grass for weeks as the plants process the hormone application.

There are other products that have been developed in South Korea and the United States which provide a gentler control including PoaCure and Xonerate to name a couple. However, none of these products have received approval for use in Canada by the Pest Management Regulatory Agency.

A more extreme approach is a complete rebuilding of putting greens for more established infestations. When completing this process, the greens surface is stripped off and disposed of. And at this point the soil is either fumigated to kill off any ungerminated seeds in the soil or the entire green cavity needs to be dug out and replaced to remove any ungerminated seeds. However, this process is just a ‘reset’ not a cure.

Growth regulators can be used to manage poa. Plant hormones are sprayed over the entire greens surface and once taken up slow the vertical growth of plants down in hopes of mitigating the bumpier afternoon greens. These products will also stunt seed head production. However, they can also increase the density of Poa plants by creating more plants causing this approach to be a bit of a double-edged sword.

Finally, some superintendents will attempt to use environmental stress to control newer infestations. Knowing that Poa is less tolerant of drought, superintendents will push their greens to the brink of drought damage, hoping to kill off the Poa before the bent grass is affected. This process can yield mixed results at best.

In closing, Poa annua is a fickle thing. It can give you some of the best putting greens in the world when everything goes right. Sometimes it is a necessity for shaded green sites. Likewise, it can become very troublesome for afternoon rounds and for superintendents managing it in the winter and summer. However, one thing is for certain, at some point Poa annua will creep into your golf course and it will have to be managed one way or the other.