I like this photo because it sums up the strengths and opportunistic nature of Poa annua. This spot is on the 7th fairway, and is about to be solved by a substantial drainage project this winter. The thin area you see in the photo spent a majority of last season submerged in water. I refer to small depressions like this in fairways that hold water as “bird baths.” It seems like the common sense thing to do, would be to raise the sunken area to the level of the surrounding turf. Unfortunately, it’s not that easy because when that is attempted, the low spot is often pushed a new area, within feet of the original spot.
Regardless, you can that grass has begun to fill in the void. The turf you see just happens to be Poa annua, or Annual Bluegrass. The reason Poa annua is filling this void is because it is far more tolerant of poor growing conditions compared to other grass species. This could mean a very wet area like we see here or a heavily shaded area that we see in other areas of the golf course.
One reason Poa annua is so difficult to eradicate is because it is so adaptable. It can acclimate itself to all kinds of growing conditions. I often say that the best weed control is dense turf. If you look at the surrounding turf on #7 fairway, you’ll see a dense stand of Creeping Bentgrass. Poa annua seed has a difficult time germinating and developing into mature plants when it’s in constant competition for water and nutrients in an already established turf.
However, Creeping Bentgrass requires full sun exposure to be dense and healthy. Once that stand of Bentgrass becomes compromised because of shade for example, it will begin to thin. Once thinning occurs, Poa annua will take advantage of that opportunity and move right in. It will eventually out compete the desired Bentgrass. I have said for years, if Highlands CC ever had interest in regrassing its greens to a new variety of Bentgrass, the first thing that needs to happen is to develop an aggressive program that ensures every single putting green is receiving 10 hours or more sunlight each day. Until that happens, Poa annua will always be a challenge on our golf course.
You can also see by the photo that Poa annua has a “bunch type” growth habit. All bunch type grasses like Poa annua are established and spread by seed. Compare this to Creeping Bentgrass, which spreads by way of stolons. A stolon is sometimes referred to as a runner that creeps along the ground, producing new shoots. Warm season grasses like Bermudagrass are even more aggressive, spreading by both stolons and rhizomes, above and below ground runners, respectively. Anyone from the deep south can appreciate this when you think about your lawn service edging your walkways at your home. They can get covered, quickly!
Again, it’s an interesting photo that I thought would give you a better idea of the unique ability of Poa annua.