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The use of plant growth regulators (PGRs) in suppressing seedheads has grown in popularity. The theory is seedhead suppression creates heartier plants due to the misdirection of energy away from seed production and into plant reserves.
There are other methods besides PGRs for suppressing seedheads, such as verticutting and topdressing. However, PGRs alone can be quite effective. The trick is application timing, which has to be precise.
According to a study conducted by Tim Murphy (University of Georgia), Ted Whitwell (Clemson University), L.B. McCarty (Clemson University) and Fred Yelverton (North Carolina State University) titled, “Plant Growth Regulators Used in Turfgrass Management,” PGRs, when used for seedhead suppression, must be applied before seedhead formation and emergence. Applications made after seedhead emergence will not be effective.
The study goes on to offer recommendations on timing for different turfgrasses. For Bahiagrass, for instance, mowing should occur as seedheads emerge – usually from May to mid-June. Then, PGRs should be applied about 10 to 14 days following mowing or just prior to new seedhead appearance. Additional applications six to eight weeks later may be required if new seedheads begin to emerge.
For creeping bentgrass golf greens, the study recommends applications be made during periods of active root growth – mid-fall and spring in the southern U.S. Applications should not be made during mid-summer and mid-winter months. On warm season turfgrasses, such as Bermudagrass, the appropriate PGR should be applied to actively-growing turfgrasses after full spring green-up and several mowings. Applications can be repeated during summer months if additional growth regulation is needed.
So what is the appropriate PGR to use? According to Todd Bunnell, golf market manager of SePRO, there are two types of PGRs: those that inhibit the overall growth of the plant, and those that are used predominantly for seedhead suppression or the “abortion of seedheads.”
“It comes down to the long-term objectives of the superintendent in certain areas, whether they be fairways or greens,” Bunnell says. “If they want to maintain Poa, they will likely use Primo and then Proxy or Embark to manage the seedheads as they go through the growing season. If they want to reduce the Poa population, then PGRs such as Cutlass are effective to do that over the long-term of one to three years.”
Many superintendents will apply Cutlass in a program over an entire year, Bunnell explains. At the onset of the Cutlass program on fairways, superintendents might have 50 percent Poa annua. If they apply Cutlass throughout the entire year, then they might only have 25 percent Poa the following spring. If they follow the same program the following year, they may go down to 10 percent Poa.
“If a superintendent can go from 50 percent Poa to 10 percent over two years in fairways, once they get to the 10 percent level they may not even need to apply Embark or Proxy. So a more long-term fix to reduce the Poa population eliminates having to use some of the Poa seedhead inhibitors.”
The cell division inhibitors are also called Type 1 PGRs and, according to the previously-referenced study, inhibit growth rapidly, within four to 10 days and lasting three to four weeks depending on the application rate. However, the study cites phytotoxicity or yellowing as a problem, which is why the PGRs are used primarily on low and medium-maintenance turfgrass areas. However, the yellowing is not a problem that can’t be overcome.
John Gallagher, superintendent of Race Brook Country Club in Orange, Conn., has begun experimenting with applications of PAR mixed in the tank with Embark or applied a few days after the application of Embark to mask the yellowing. He also uses more potassium sulfate to keep the turf green in colder weather without surges of growth.
“The biggest challenge I face regarding the suppression of seedheads is explaining to the golfing membership why the turf goes off color once the Embark takes effect,” Gallagher says. “I write articles to the membership and post photos and relevant magazine articles. I think I’ve been using Embark for so long that the membership doesn’t remember what it’s like to play or putt on turf that’s gone to seed.”
Another method to reduce the temporary yellowing is tank mixing Embark with Ferromec AC Liquid Iron, which contains nitrogen, iron and sulfur. When Ferromec is added, seedhead suppression has reportedly decreased by 10 to 15 percent.
For the past 15 years, Gallagher has pretty much followed the same routine to suppress seedheads. He applies Embark roughly the first week of April to greens, tees and fairways but in that application is also a fungicide for leaf spot prevention and liquid iron to keep the turf green. After about a week, he topdresses greens and lightly grooms over the next few weeks to help remove any seedheads that appear. He may verticut depending on the weather but he usually doesn’t that early in the season. He also may apply Embark again if the weather gets unusually warm about three weeks after the initial application in order to stay seedhead-free. About 10 to 14 days after that, he begins his Primo and Cutlass season-long applications to greens, tees and fairways.
The issue to be wary about with verticutting is potential damage to the turf. Verticutting can eliminate some of the seedheads on a putting green after emergence, but this tactic doesn’t prevent the formation of seedheads. The equipment must be properly adjusted to avoid damage to the turfgrass plants, and the mechanical removal of seedheads will need to continue until seedhead production ceases.
In Gallagher’s region, timing PGR application is very tricky because in the Northeast, the weather doesn’t cooperate a whole lot in April. He has found, however, that the timing isn’t as critical with Embark.
Jim Ryerson, superintendent of Two Oaks North Golf Club in Wautoma, Wis., agrees that timing can be a challenge.
“In Wisconsin, no spring is ever normal,” Ryerson says. “Last spring was very cold, very wet and very snowy. We verticut a couple of times, but couldn’t topdress very often with the wet weather.”
Ryerson was sort of a stranger to seedhead suppression as he had never had to do much about it because it had never been much of an issue. But that all changed during the last two to three years. He first used Primo Maxx, verticutting and topdressing. Last spring, however, he used Embark and, after calculating the GGD (growing degree days), applied 30 ounces per acre on May 12. He then made an additional application three weeks later on June 6 and says it worked pretty well.
“I think you need to verticut and topdress along with applying PGRs as the plants are quite aggressive at that time,” he says.
Gallagher, however, says that PGRs alone seem to be his solution to seedhead suppression.
“I experimented with other PGRs for two years to test new theories and products, but found that success was too dependent on perfect timing and cooperative weather,” says Gallagher, who counts Embark, Trimmit, Primo and Cutlass in his PGR arsenal. “With the right one, however, it could be all you need.”
Gallagher had also cited cost as an issue at one time, but the cost of PGRs is now about half what it was a few years ago due to the active ingredient Trinexapac-ethyl, the main component of Primo Maxx, recently coming off patent.
To get the timing just right, superintendents are encouraged to seek advice from their local product representatives and extension agents to figure out application dates based on degree days, historical data and physical observation.
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