As the South prepares itself for another peak season, golf course superintendents need to be aware of potential disease pressures they may face. While factors such as topography, climate and turfgrass variety play roles in a particular disease’s tenacity, turf experts provide their best forecast.
Superintendents maintaining Bermudagrass putting greens should be vigilant this fall, says Dr. Jim Kerns, assistant professor and extension specialist of turfgrass pathology at North Carolina State University. “The Bermudagrass guys, they’ll be starting to see things like leaf spot, Pythium blight, take-all root rot, and even potentially some nematode issues,” he says.
When it comes to warm-season grasses, Dr. Bruce Martin, Clemson University professor of entomology, soils, and plant sciences, is particularly concerned about Pythium.
“We are recognizing an increase in the visual symptoms of patches in Bermudagrass greens that appear to be caused by Pythium,” he says. “This is in addition to occasional outbreaks of bonafide Pythium blight. Symptoms of Pythium root rot are difficult to distinguish from some other patch diseases or even root knot nematode infestations. Also, with abundant rains and cloudy weather in the past in fall months, we likely see more severe spring dead spot the following spring but also have seen a big increase in take all root rot.”
Take-all root rot is another pest for superintendents’ disease radars. It’s troublesome in southern climates because its initial impact occurs below the surface.
“Last fall, Hurricane Matthew came through and really swamped the Carolinas and, of course, Florida,” says Dr. Derek Settle, a technical specialist for Bayer who is based in the South. “We got to see some of that this year with these tropical storms that are moving up through the Gulf and along the coast. That changes things because suddenly you’ve got saturated root zones and then you’ve got problems.
“But it’s never really readily apparent, and that means by the time we see symptoms above ground it’s probably been weeks to a month of activity,” he adds. “In this case, by the (fungal) pathogen Gaeumannomyces (take-all patch) and it’s a very common disease that attacks all the warm-season turfs.”
The introduction of ultradwarf putting greens has made take-all root rot a more pressing concern, says Syngenta senior technical representative Dr. Lane Tredway. “Take-all root rot has historically been a problem only in the Deep South,” he says, “But it has become a chronic issue on ultradwarf greens in the transition zone.”
Take-all root rot causes patchy symptoms from fall through spring when cool and/or cloudy weather suppress Bermudagrass growth, Tredway says. But this is not necessarily the best time for preventive fungicide applications because the pathogen is most active from late summer through early fall.
Cool-season grasses in the transition zone generally aren’t as susceptible to disease pressure as strains of Bermudagrass, Kerns says.
“On bentgrass, we do see residual problems from the summer that still may need control,” Kerns says. “But bentgrass down here, their biggest months are July and August. If they can get through that, they’re pretty solid.”
Superintendents caring for cool-season grasses must remain vigilant. The combination of high heat and high moisture drives epidemics of Pythium root rot in summer months, Martin says, which can be a major limiting factor regarding survival of bentgrass greens in the South. These factors may also provide conditions which limit fungicide efficacy, so a breakthrough of diseases such as summer patch or fairy rings can occur. So, the major chronic diseases on cool-season grasses to plan for year in/year out would include dollar spot, fair ring, anthracnose (especially in Poa), rhizoctonia-induced diseases and especially Pythium root rots.”
Kerns advises that superintendents should make their stand against the pathogen when their courses are busy. “I would kind of not worry as much about dollar spot in July and August as I would in September and October,” he says. “Golfers are coming back to the resorts and even down in Florida it’s been an issue on grasses like Seashore paspalum.”
Dollar spot can be severe in the spring and fall when there is a lot of golf being played at southern latitudes. Kerns suggests superintendents facing budgetary issues focus their efforts against dollar spot during those times and cut back if need be during the heat of the summer. “(Dollar spot) is rarely as severe down south during the summer,” he says.
Tredway says hot, humid weather has become a more pronounced superintendent concern in recent years. “Absolutely, without question,” he says. “Turfgrasses are most susceptible to disease when they are stressed, so weather extremes, which seem to occur now with more frequency, lead to aggressive disease outbreaks. Hot and humid summers cause creeping bentgrass to become very susceptible; conversely warm and wet winters create ideal conditions for Bermudagrass diseases.”
When Settle first started working for Bayer in 2013, the winters in his territory featured cold periods and significant amounts of snow. But the weather trends have changed the past few years.
“It’s been all about heat,” he says. “So, we aren’t really having winters and that has impacted us.”
Settle says warmer winter temperatures have led to increased diseased pressure from take-all root rot and Pythium, among other things. Sustained cloud cover also contributes to the problem.
Superintendents shouldn’t be afraid to call an audible if the weather dictates. “If you see the weather forecast bringing in a big storm or we have a winter where there are warmer temperatures, you’re going to have to change up what you’re doing,” he says. “You might even (make) an application where you never have before in your career.”
All superintendents will face the risks of disease pressures as they head into their golf seasons. But how should they minimize those risks? Tredway says the best defense is employing sound year-round cultural practices.
“Good cultural practices are the most important part of a disease management program,” he says. “Turf that is constantly stressed from low fertility, drought, poor soil drainage or close mowing will be more prone to extreme weather conditions and the disease outbreaks that often follow. If the turf is properly conditioned to be healthier and stronger going into that stress period, it will perform better and recover quicker from the stress with better quality.”
When it comes to applying fungicides, Tredway advocates a proactive rather than reactive approach.