Tips From The Pros

POA ANNUA IN SPORTS FIELDS

Poa annua (aka Annual bluegrass) is considered a grassy weed in natural grass sports fields. You know what it is, so this isn’t a botanical description of this grass. Rather, I hope to offer here a few useful tips in consideration with overall sports field management in battling this potential (inevitable?) pest.

Why we don’t like Poa annua.

Poa annua seems to come into your natural grass field out of nowhere. It can blow up in a single season from a small amount to a problem. It is a tenacious organism and usually a profuse seeder. It’ll compete at the lower heights of cut favorably. Once established in a field, the surface will look blotchy and the ever-present seed-heads are also considered unattractive. You lose the consistency of your look. It tends to have a lighter green color than our commonly used sports field species and varieties, at least here in the US. More importantly, Poa annua tends to be a weak, shallow-rooted grass. It’ll blow out easily once it gets into a field. I can’t imagine a grass field playing consistently once Poa annua has established itself. The result may be reduced carrying capacity of the field, as it will wear out much quicker than bluegrasses, ryegrasses and bermudagrasses. It does not do well in the summer heat. It seems to be especially prone to disease and insect pest damage.

If you’ve ever been “overtaken” you know what I mean. The first football field I ever managed was a training field that was predominately inherited Poa annua. That thing tore up in pelts! Over the years I fought it. Then it followed me to a new set of sand based fields. We tried lots of control measures, even trying to burn it out with an acetylene torch. It takes a lot of heat to cook a Poa annua plant! We tried a couple of chemical controls available back in the early 90’s, but all we could accomplish was even weaker and uglier Poa annua.

Fast forward to 2017 and we have many more-effective chemical control choices in battling Poa annua. Here is a good review of chemical control strategies for Poa annua in SportsField Management magazine by Dr. David Gardner of The Ohio State University.

For this blog, I’ll focus on what my experiences tell me is the only way to keep Poa annua at bay in your natural grass playing surface. Mechanical control, to me, is the only thing that works.

Dig it out in an all-out, year-round assault on its very existence!

On my third field, I finally figured it out and won. We had a fiber-reinforced rootzone playing surface that meant we could not dig out a few inches and sod. If Poa annua took over, it was there to stay.

Here’s what I learned:

Don’t ever let it get a beachhead, or well established anywhere on the fields. This weed is a profuse seeder with great genetic variability and adaptability. Dig it out as soon as you see it, don’t wait a minute.

Do the Poa Wiggle. Learn to spot those seemingly ever-present seed-heads whenever you are on the field and teach your entire staff to do the same. The key is to pull the little plants out when they are still small. The technique I like is to get down on hands and knees and start “gathering” the Poa annua plant. Pull up all its shoots, realizing that they tend to weave into your desirable turf. Pull up all the shoots into a bunch pinched between thumb and forefinger, isolating a single plant or bunch of plants. Think of a tied-up Christmas tree in a tree lot. Get a good grip at the base and begin to strongly wiggle the whole plant, roots and all, out of the turf. The shallow-rooted buggers will usually just pop right out, leaving only a small depression opening in the turf that can be easily pressed out with your foot.

Once the small bunches grow into a patch (maybe > 1” dia.), the wiggle technique no longer works. Now you’ll have to dig out the patches and re-establish grass in the open soil spot left on your field. Using a template cutter and sod plugging from desirable turf off to the sides of the field is a common way to quick-repair patch spots of 3 inch diameter or larger. Make sure you cut the plugs deep enough so that your surface repair will hold up for the type and level of play on your fields. Smaller openings in the turf might be better if filled to grade with a good divot mix of soil and seed.

Once the small bunches of Poa annua have coalesced into large patches of a foot or more in diameter, or have populated the turfgrass to the point that digging and plugging are impractical, it’s probably time to start planning a re-sod or look into some of the chemical control measures. Sod is a comparatively expensive but effective control for annual bluegrass and many field are completely re-sodded just to eradicate it. Sod repair and scheduled full field re-sods every few years may be all it takes to keep annual bluegrass at bay. Targeted herbicides and other control methods will work better if you don’t wait to be overtaken.

Turf Tips 101: More Tips on Poa annua Control in Sports Turf.

Once this perennial-like annual grassy weed gets in your playing surface, the longer you wait-the tougher and more expensive getting it out will be. So don’t wait. Make early mechanical eradication an important part of your overall turf management program. Teach every turf team member to identify and wiggle-out Poa annua whenever they see it, while it’s small enough to wiggle out.

I’ve dug out Poa annua on national TV game days, I don’t care. If you were walking across the field talking with me, there was a good chance I would drop to a knee suddenly to get one Poa annua plant out. You might be mid-sentence, but I’d just drop and pop. Once you walk by a Poa weed, you may not be able to find it again later. We all know that mowing a grass sports field is also a great field inspection exercise. We used brand new (unkinked) sprinkler flags as “lawn darts”. Each mower had several on board. When mowers would notice any Poa annua plants, they would throw and stick a sprinkler-flag dart near it (after they had mowed that area of course). After mowing, go back and pop them out and collect the flags.

Two to three times a year, we would schedule a “Poa walk”. This involved the entire turf team each with two buckets and a sod knife. The first bucket had a good divot mix with seed and a cup for scooping and filling. The second bucket was for collecting and disposing of the Poa plugs you dig out. Start at one end of a field and slowly walk each mower swath, digging out every plant you find-either with a wiggle or cut, whatever it needs. It is a slow process, maybe several hours per field. But you don’t have to do the whole thing in one day. Get it an hour or two at a time, whenever you can, taking notice of where you finish each day so you know where to start the next.

Note that Kentucky bluegrass seed heads look somewhat similar to Poa annua seed heads. KB is usually a late spring seeder, and so doing your Poa walks at this time can prove difficult. Usually be early summer, KB is done seeding and you are back on your tenacious Poa control program.

In warm-season grasses and climates you have an advantage in that after your desirable grass (e.g. Bermudagrass) has gone dormant-brown for the winter, Poa annua will stay green and growing, making it very easy to spot and eradicate either mechanically or chemically.

A “Poa walk” is also a great way for turf team members to get to know each other. No loud equipment, few safety concerns. Just a slow walk, a time to talk, and pop-out some Poa annua. My experience is that 1-3 Poa walks per year will generally keep things at bay, but the work never ends and you have to be diligent-hitting anything you see between Poa walks right away.

Beachheads may form in the usual areas or may move around year to year, but they are often gained in any poorly draining areas of the field. Poa annua is shallow-rooted and likes wet feet. Good drainage, especially at the surface can keep thing too dry for Poa annua, but not the grasses you want. Many sports field turfgrass stands are drainage-challenged as the sports and events traffic tends to compact the surface first.

Poa annua likes an opening in your turfgrass to get established. Like any grass establishing from seed, it has a tough time competing with tough, well established adult turfgrass. Thick healthy grass is a great Poa annua control strategy. Again, this is often a challenge on trafficked sports turf.

You have to get most of the roots out when mechanically controlling Poa annua. Fraze mowing or otherwise scuffing the surface of your grass sports field solely to eliminate Poa annua works only for a growing season or so-in my experiences. You have to mechanically remove some of the roots and soil, in my opinion, even though Poa annua is not known for underground growing points like rhizomes. I believe you also have to get out viable annual bluegrass seeds that may have accumulated in the top ½ inch of the soil. The good news is you only have to go ½-1 inch deep in most cases.

Despite all the hate, Poa annua is a decent deep winter sports field grass. Not known for cold tolerance, it is a plant that does pretty well in December and January in my experiences, depending of course on the climactic details. Then it seems to be quite prone to late winter or early spring cold snaps. Strange plant.

Resources of the Month

How to identify Poa annua from NC State TurfFiles

Poa annua may be the most widely distributed grassy weed in the world.

Michigan State University Turfgrass has a good page on Poa annua. Click tabs at top for more info.

End Quote

“My years of experience have left me less confident that we will ever find an answer to the problem. It is likely that we will never see a completely effective “magic bullet” that will eliminate it.”

-Dr. Nick Christians in this 2015 issue of SportsTurf Magazine on Poa annua in sports turf.