Wherever your golf course is located, the wacky winter weather this year will affect how you manage the risk of dollar spot infestation (Sclerotinia homoeocarpa).
Along the Eastern seaboard, 2016/17 was a warm winter. The usual January snows did not show up until mid-March, and then Mother Nature did a 180-degree turn and things warmed up again. Temperatures in Atlanta dove to 20 degrees just before St. Patrick’s Day, only to rebound.
The result is that warm-season grasses in several areas showed signs of cold injury. In most cases, the grass will grow out of the damage. However, green-up could come early to those areas where it got very warm very quickly. That will put extraordinary pressure on the turf and its ability to resist disease.
“With this winter’s weather, we might see some dollar spot earlier than usual,” said Brandon Horvath, turfgrass pathologist at the University of Tennessee.
Several new fungicides are available to help superintendents fight dollar spot. Pinpoint, from Valent USA Corp. and Nufarm, is one product that shows solid promise. Registered in October 2016, Pinpoint is mandestrobin, a strobilurin (QoI) fungicide that specifically controls dollar spot. QoIs in FRAC group 11 are best used preventively in rotation with other classes of chemistry, such as spectrum succinate dehydrogenase inhibitor (SDHI) fungicides.
Another possibility is Kabuto, a new molecule that can be alternated with DMI-class materials. Distributed in the United States by PBI-Gordon, isofetamid offers both preventive and curative benefits.
Exteris Stressgard from Bayer also is on its way to market. It is SDHI-class chemistry. In addition to dollar spot, it also is effective against brown patch and leaf spot. Limit use to one back-to-back application before using another chemistry.
“We have more dollar spot fungicides on the market for superintendents to choose from. Understand the chemistry and understand its properties,” said Steve McDonald, consulting plant pathologist with Turfgrass Disease Solutions, Spring City, Pennsylvania. Of the three newest materials, he has tested Exteris and found it worked well in his trials.
Many of the new materials are broad spectrum. However, because they have such nice activity, McDonald cautions superintendents not to overuse a specific material just because it is effective against many disease pests.
Chemicals are not always the answer to dollar spot challenges. “If you are dealing with Bermuda grass or Zoysia grass, look at your moisture management,” said Clint Waltz, extension turfgrass specialist at the University of Georgia experiment station in Griffin. Most greens and fairways are fairly well managed for water. Where dollar spot can get a foothold is in the marginal areas: roughs, the out-of-play areas, and even on the driving range.
“A bit of malnutrition will favor dollar spot,” Waltz said. He recommends applying between a half-pound and three-quarters of a pound of Nitrogen per 1,000 square feet to “see if that squares things up.”
McDonald said he expects dollar spot in the mid-Atlantic to behave normally this year, with superintendents spraying from mid-April to mid- to late-May. While diseases appeared to be well ahead of schedule early in March, the cold snap in mid-month got turf back to more normal conditions.
“Anything you can do to displace dew is worth doing,” McDonald says. “Rolling or dragging will move moisture from grass and help minimize dollar spot.”
Tennessee has seen dramatic increases in dollar spot when fertilizer levels drop from the typical 5 or 6 pounds per 1,000 square feet down to 3.5 pounds or less. “Be sure your fertility levels are optimal. Weak fertility makes dollar spot more damaging,” Horvath said. Serious dollar spot, with pitting of the grass, is often the result of weak fertility. Well-fed grass can grow out of minor damage on the leaf surface.
Last year, Georgia was fairly dry. As a result, there was not much dollar spot on golf courses.
Ironically, that turned into a big problem for those studying the disease.It was so dry that University of Georgia scientists could not get dollar spot to materialize in their research plots. They even inoculated the plots, but they simply could not get dollar spot to challenge the turf.
It was so hot and dry that the warm-season grasses in several areas went into drought-induced dormancy very early. “That means they will be a bit weaker than we’d like this year,” said Waltz, adding that aerification is one possible remedy. “Open the soil and stimulate growth,” he advised.
Meanwhile, Horvath’s advice is to cut fertility on the plots and then add inoculum. Low fertility favors dollar spots. Where dollar spot is unwanted, “Superintendents should be sure their fertility levels are moderate but not lean,” he said.
There may be a true predictive model for dollar spot available soon. The North Carolina State University program has not yet been published but it has been subjected to field trials in several areas of the country with good results. Some models severely underestimate outbreaks, leading to turf disasters. Others overestimate dollar spot, which is a safe but expensive strategy in areas where infestation can occur one year but not the next.
“It’s nice if you can save a spray or two,” Horvath acknowledged. However, missing an application on putting surfaces probably is probably more risk than most superintendents are willing to accept.
In the North, where there is some tolerance for minor infestation in fairways, there is an economic incentive to save a few thousand dollars on a spray and put up with a few stray spots as a result.
“Models can be useful,” McDonald said, but he cautions that their success will vary by location. “They are a good tool to time and justify applications. Nothing will replace the superintendent’s on-site observations and experience.”