Many folks have noticed their lawn has suddenly turned green, and the grass is not coarse and ugly. However, this species of annual grass is the most difficult to control and most obnoxious weed in golf courses.
The culprit is called annual bluegrass (Poa annua). It grows voraciously in cool weather. Around here it is rarely a problem in summer, but it can take over desirable turf and squeeze it out, allowing other weeds to establish when warm weather begins.
Annual bluegrass produces tremendous quantities of seed, and it does so at any cutting height. Even on golf greens cut at less than a quarter inch annual bluegrass can produce seed. On your average home lawn, it’s not a problem, because most folks aren’t as discerning. Eventually it will blend in with the rest of your turf environment.
My dad always said that if his lawn was green it was fine. Golf course superintendents take a different view. Annual bluegrass can greatly influence how a green will play, to say nothing about how it looks. Golfers don’t pay huge country club membership fees to play on substandard turf.
Frequent irrigation will make annual bluegrass flourish. That’s why it’s such a problem on golf courses. It’s also why it springs up around here in late winter and early spring. Soils are usually wet, and this year is no exception.
Killing Poa annua with herbicides is difficult for multiple reasons. First, its seeds are everywhere and killing a patch of this weedy grass only creates a bare patch for new seeds to germinate. Annual bluegrass seeds can lay dormant and viable for six or more years.
Also, many herbicides that will kill annual bluegrass also injure other grasses, particularly cool season ones like fescues and bentgrasses. Creeping and velvet bentgrass are common species for greens in cooler regions. At high application rates these herbicides could do more than injure the desired turf. Additionally, most effective herbicides are restricted use and must be applied by professionals.
Fortunately, bermudagrass is more commonly used here for golf greens and sports fields. It’s dormant now, making spot treatments for annual bluegrass more effective. Still, the biggest problem is the high natural supply of seed coming from adjacent places.
Using pre-emergent chemicals like those used to prevent crabgrass can be effective to control annual bluegrass. However, that should be done in fall, not now. Now is the time to prevent crabgrass, a warm-season grass.
One non-chemical method for controlling annual bluegrass long-term is to establish a higher cutting height for your lawn. If cutting height is maintained at three to four inches there will be less light penetration. This will mean weed seeds will have a tougher time germinating and competing for light. Complete control will take a few years.
For those like my dad who only care about a lawn being green, the only real problem with this weed is that you will have to start mowing your lawn sooner than you want to. I’ve already mowed mine and it’s only early March.
Ted Manzer teaches agriculture at Northeastern High School (firstname.lastname@example.org).