Our Newest #1 Turf Weed
Actually, it's not new, because it's been around for at least 12 years, but it's growing in it's ability to ruin the perfect sward. It's called "European bluegrass", or "roughstalk bluegrass", which are polite names for Poa trivialis. Most of us just call it, "triv." It is a bona fide cultivated bluegrass variety, often found in "shady mixtures" (not ours!), and it's a frequent contaminant in Kentucky bluegrass seed, and even turf-type fescue seed. Because of it's floppy habit and lime green color, it looks particularly offensive in a nice sward of dark green Kentucky bluegrass. It's not quite as noticeable in turf-type fescue because the fescues are a medium shade of green. The picture below shows a small patch of triv in Jeff's front yard. The dark green, low growing species is Kentucky bluegrass (Poa pratensis).
Poa trivialis
In the "good ole days" yellow nutsedge enjoyed the distinction of being the "worst weed in St. Louis." But nutsedge can be controlled very effectively with halosulfuron (Sedgehammer
®+). Unfortunately, there are no selective herbicides that remove triv from cool season turf species. Jeff has tried three different herbicides, with reputed efficacy against this bugger, but the triv just laughed them all off. Botanically, Kentucky bluegrass and triv are closely related (kissin' cousins), and thus, no herbicide can eliminate one without harming the other. Roundup
® will kill both, though.
This nasty weed grows very rapidly in cool, cloudy weather. It commences it's growth earlier in the spring than either Kentucky bluegrass or turf-type fescue. It will usually go dormant after just 3 weeks of stressful hot and humid weather, thus it ensures its survival as soon as cooler, wetter weather returns (September and October here in STL). It spreads very rapidly by rhizomes, and can make very large patches in short order. When that large patch goes dormant in July and August it'll leave a huge bare spot in your sward. UGLY, UGLY, UGLY! This grass tolerates short mowing, too, and you may notice that it looks really crappy after you've mowed at your normal mowing height. It's a "floppy" grass...not capable of standing erect like our bluegrass and fescues, at our mowing heights (>2 inches).
There's another bluegrass weed, Poa annua, referred to as "Poa" or "annual bluegrass." Golfers in particular hate this weed because it's a serious problem on putting greens. It'll actually interfere with the path of the putt, thus decreasing the golfer's accuracy on the green, increasing their score...and we all know that golfers tend to take their frustrations out on the greenskeeper! This weed isn't the same as triv, but it's just as much of a pain in the ass. Annual bluegrass tolerates compacted soils and spreads itself very effectively via seed production. It'll grow in those areas that you frequently scalp with your mower or string trimmer. It can grow in compacted soil, such as along a driveway, where your wife repeatedly runs her front tire along the grass (despite your best effort to provide remedial instruction...aka, "training"). It's not as ugly in Kentucky bluegrass as triv, but when it dies in August it can leave brown patches. There are chemical solutions for controlling Poa annua, but only for professional applicators and groundskeepers, not the homeowner.
The shot below (again, Jeff's yard) shows the visible difference between these two Poa weeds. Triv is distinct in it's filthy lime green coloration, and it's ability to spread rapidly. Annual bluegrass is distinct because it grows in small patches (at first) and produces its seed heads before any other turf species (past two weeks or so). It has a dark green color.
Poa trivialis (foreground) and Poa annua (background)
If you want to do something about triv, your ONLY OPTION IS THE NUCLEAR OPTION. You have to press that big red button NOW, before the triv starts going dormant. You have to spray your entire yard with Roundup. Wait about 4 weeks, and spray it again. Three weeks after that you can reseed, but be sure to use a certified seed blend. Reseed at a light rate, as seeding in the heat of summer usually doesn't work too well. You'll kill off your "temporary" turf with Roundup again, in late August. Finally, around Labor Day, you can reseed with a quality seed blend. If you don't start now, you'll miss some of it, because it will start going dormant with the summer heat, escaping your nuclear warfare (Roundup).
A true story: Jeff went nuclear 4 years ago, in an attempt to rid his front and side swards of triv. He made the mistake of timing his first spray in mid-July, because the triv appeared to be growing vigorously. (BTW, his wife was very pissed, thinking him an moron for killing what appeared to be a decent lawn--at least to her untrained eye). Jeff reseeded in early September with some very expensive bluegrass, and went through the fall thinking he defeated this villain. However, just as the new bluegrass started to thicken the next spring, the triv roared though the new sward, and consumed his yard, stronger and thicker than before.
Moral of the story: Go nuclear, ASAP. Be sure your wife is on board, first!
The Reseeding Bible
Controlling Nutsedge
Moles & Their Control
Irrigation Tips
Our Newest #1 Turf Weed
Controlling Crabgrass
Controlling Adult Japanese Beetles
Know Your Sward Size
Soil Science Basics
