What, Weed Worry?

The autumn season is no time to fall down when it comes to controlling and pre-treating weed pressure. And for southern golf courses, the turn toward Labor Day provides little respite for course management, with fickle weather patterns requiring a studied game plan as soil temps approach 70 degrees.

“Going into this time of year, prior to winter, people should be looking at anything they can do to reduce the weed population,” says Dean Mosdell, technical manager of the Western U.S for Syngenta. “Some of these perennial broadleaf weeds, the best time to control them is heading into fall rather than waiting until spring because you’ll get better translocation of the active ingredient down into the roots. Come spring, they’re putting out a lot of growth and not translocating material down into the root system.”

Prepping for autumn isn’t predicated on herbicides alone. Rather, your preemergence plan should combine applications with a review of spring data, along with study of irrigation systems, shaded areas and mowing heights.

With Poa annua at the forefront, here are five weeds to ready for as summer turns toward fall on southern courses.

Poa annua

Annual bluegrass is a burden, to be sure, appearing from tee-to-green and proving especially pesky on putting surfaces.

“The number one weed is Poa annua,” says Dr. Shawn Askew, associate professor of turfgrass weed science at Virginia Tech. “There are many different ways that Poa can cause problems on a golf course, and now, in the southern states, there’s also a massive problem with herbicide resistance in annual bluegrass.”

Evidencing the adaptation of Poa, Askew says if you’ve had success with Prograss for about three or four years in a row, then you’re probably not having success with Prograss anymore, because annual bluegrass becomes resistant quite rapidly to that product. “And the further south you go, the more difficult it is because Prograss relies on winter temperatures to help; so it can fall short if you have a mild winter,” he says.

Mutation makes annual bluegrass even more of a nuisance. “The weed has developed biotypes that tolerate low mowing heights,” says Kathie E. Kalmowitz, Ph.D., technical specialist, turf and ornamentals Southern Region for BASF. “However, the bunch type is a prolific seeder and plants can germinate over several weeks if the weather conditions in the fall are favorable.”

To best control winter germination of Poa, superintendents need to have a plan in hand and the best bet for management is putting out a preemergence herbicide prior to seed emergence. The plan may also be well-served by rotating applications to avoid resistance.

“Application timing varies widely depending upon soil temperature and available moisture, but typically superintendents apply between September and October,” says Dr. Jay McCurdy, assistant extension professor of turfgrass sciences at Mississippi State. “There’s limited options on greens, but the best prevention is to keep the remainder of the course clean. After that, winter time postemergence applications to control escapes are almost always warranted.”

“Pendulum, Pendulum + Tower, or Freehand G have activity on annual bluegrass,” says Kalmowitz. “Pendulum and Freehand are WSSA herbicide groups 3 or 3 + 15 herbicides, and it’s the DNA’s or Group 3 herbicides that have, over the long years of their use, lost some sensitivity to controlling this weed. Timing is very important and if the golf course has practiced a good rotation of herbicides at the property for several years, the DNA’s and Pendulum or Freehand can be very effective.”

Bermudagrass

From fairways to rough areas to green encroachment, Bermudagrass is a prevalent pest. For non-green areas, Bermudagrass removal is typically a multi-year autumn project.

“In the southern transition zone, normally it will take two years of the fall schedule to remove the Bermudagrass, or, reapplication to Bermudagrass again in the spring when the grass emerges from dormancy and the cool season turfgrass is growing vigorously,” Kalmowitz says. “Reseeding the cool-season turfgrass in the fall allows for inter-turf and weed competition and removal of Bermudagrass can be greater with this technique.”

From the Atlanta, Georgia region and upward, Bermudagrass (and Wiregrass) encroachment in tall fescue is often a problem.

For cost-efficiency, Askew advises using Tenacity turflawn when Bermudagrass gets 50 percent green in early summer to pre-treat, followed by combining an ounce of Pylex and 32 ounces of Turf Line applied in three-week intervals come fall.

“But if you have severe infestation of Bermudagrass and you need to seed tall fescue, it’s important to know that Turf Line carries a three-week seeding restriction,” Askew adds. “Our solution to that is, on your last application, do not use the Turf Line and you’re actually able to seed and spray on the same day.”

A review of mowing heights can also help “Raise the mowing height,” Askew says. “You will never control Bermudagrass in tall fescue at 2 – 2.5 inches; you’ve got to get that mowing height up to 3.5 – 4 inches before you’re going to be successful with these chemical programs. And, I understand, that golfers will then complain about losing their ball, but at lower moving height the weed is just going to be too tough to control.”

Goosegrass

After the spring emergence of crabgrass, goosegrass generally appears in bunch-growth a month or two later and is seen on course areas receiving frequent irrigation.

“Goosegrass is starting to develop more and more as a summer annual, which results in application of a preemergence herbicide sometime in the spring to control both goosegrass and crabgrass,” Mosdell says.

While goosegrass treatment on greens is particularly-delicate business, a thorough review of mowing strategy (“Goosegrass competes better at low mowing heights,” adds Mosdell), combined with herbicides can help superintendents get a grip on the goose.

For goosegrass on greens, Anderson’s Goosegrass/Crabgrass Control is a recommended option.

“And if you’re prone to goosegrass on fairways, then indaziflam may be useful,” McCurdy says. “Postemergence options during the summer requires some funds, so don’t blow all your cash up front. Cheap products are out there, but they rarely are a cure all.”

Pylex controls goosegrass and is the newest class of chemistry that has been shown to be highly effective for control, Kalmowitz says. “Because Pylex can also be sensitive to the desirable turfgrass in which goosegrass is found, controlling strategy and rate must be followed for the specific location of the golf courses,” Kalmowitz adds

Dallisgrass

Known for escaping mowing, perennial dallisgrass, often bunched in Bermudagrass rough areas in the southern region, is among the toughest weeds to best. Dallisgrass is most effectively attacked when in transition from fall into winter dormancy.

Getting the weed at its weakest is key. “Where available, MSMA is the most realistic and practical application,” McCurdy says. “Tribute Total applied twice in the fall and again in the spring works well on dallisgrass, and is also effective on sedges, and even young goosegrass.”

Doveweed

Generally seen in high-cut turf areas and found with increasing regularity in the sub-tropical Southeast, the unseemly, blue and purple flowers of doveweed can proliferate when the plant goes to seed in the fall or through cuttings that are the result of mowing.

If the weed isn’t controlled heading into August, the population can worsen the following spring.

“Most broadleaf herbicides work well when it’s very young, but it is hard to scout for under turf canopy,” McCurdy says. “Unlike many other weeds, doveweed doesn’t care how dense the turf canopy is, or if you’re following all the right cultural practices, it just jumps up and smothers all the turf competition. Celsius, Tribute Total, even MSM-Turf, all work well, but it comes back. Include a preemergence herbicide in spot treatment applications, but beware that they may inhibit recovery of Bermudagrass into treated areas.”

Superintendents can further dovetail the doveweed by attacking prior to germination.

“Then use a post emergence product containing 2, 4-D,” Kalmowitz details. “And if you are using Tower, you can tank mix the two or you can use the Post herbicide and then follow this with the application of Freehand – if granular spreadable product is preferred – or use a spray application of Tower.”

Judd Spicer is a golf writer based in Palm Desert, Calif.