Disease in a new decade

For many golf courses, 2019 was an interesting year for disease pressure. Continued changes to weather, further restrictions on chemicals and seemingly no lessening of golfer playability expectations made disease control an even bigger issue for golf course superintendents this past year.

Despite technological advances allowing turfgrass managers to control traditional diseases better and more efficiently, those other factors mentioned above have continued to keep disease pressure at the forefront of most superintendents’ radar.

We talked with researchers across the country about what they saw.

2019: A review

Lee Butler is an extension coordinator in entomology and plant pathology at NC State University and his lab receives samples from across the country.

“Overall, the total number of samples we received in 2019 was about 3.25 percent above the 12-year average for our lab,” Butler says. “So, actually a pretty typical year. 73 percent of the samples we receive are from golf course superintendents.

“As far as bentgrass samples sent in, it was a typical year where incoming samples spiked rapidly in May and declined sharply by late August. The top three diagnosed diseases were Pythium root rot, anthracnose and Pythium root dysfunction. Pythium root dysfunction bumped summer patch from the podium.

“With Bermudagrass,” he adds, “the top three were take-all root rot, leaf and sheath blight (aka mini ring), and a tie for third between spring dead spot and Pythium blight/leaf spot complex. Mini ring was the biggest surprise this year since it hasn’t been common in recent years.”

We also spoke with Dr. Brandon Horvath, an assistant professor at the University of Tennessee, about 2019 disease pressure in his region.

“I’d have to say the biggest thing I’m noticing out there – and it’s really across the board in this region – is realizing the importance of the Pythium species that cause damage on turf,” Horvath says. “Whether we’re talking about foliar blight on bentgrass or Bermudagrass, or Pythium root rot, or root dysfunction … all of these different species of Pythium that cause damage to turf. Either in the roots or on the foliage, I think we’re getting a better handle on how to manage those things.

“And,” he adds, “I think superintendents are starting to recognize that’s it’s just not the kind of thing where you can wait until you see a little bit of damage and then go after it. You really have to think ahead of time about what your management plan is going to be.”

Horvath also considers the real problem that nematodes are presenting in correlation with disease pressure.

“We know that nematode activity increases the potential for Pythium species to invade root tissue,” he says. “The threshold numbers that are published now are really nothing more than a rule of thumb. We don’t have a good understanding of the biology and why nematodes feed when they do, and then stop feeding when they do. At this time, we only have a very rough idea, and that’s because there’s just not that many nematologists studying the problem in depth. But that is starting to change. A number of pathologists, myself included, are starting to recognize how important this nematode problem is in relation to disease.”

Joe Rimelspach and Todd Hicks are from the Turfgrass Pathology Program at Ohio State University. Both agreed that the environment was the leading force for serious disease pressure in 2019.

“The spring and early summer were very wet in Ohio,” Rimelspach says, “and then the temperatures became very hot in July and many areas were dry. What we saw as a result was the emergence of two diseases: common leaf spots and dollar spot.”

Although these diseases are far from unusual in this part of the country, the conditions of the wet spring and hot summer contributed to even higher disease pressure than normal.

“Leaf spots – the common types (Bipolaris, Drechslera and Curvularia) – were prevalent on many turf situations,” Rimelspach says. “Often these leaf spots started in the spring and continued throughout the summer and into the fall. Perennial ryegrasses were especially infected and damaged by these types of leaf spots (though not gray leaf spot).

“Dollar spot,” he adds, “was set up by nearly ideal environmental conditions early in the season and persisted over a long period. On high-cut turf like roughs and some fairways, it was the worst I have seen it in years.”

Hicks agrees with his partner. “Turf managers in the northeast section of Ohio, who generally do not have a significant battle with dollar spot, found themselves suffering the same long and drawn out battle as the rest of the state,” he says.

Rimelspach and Hicks point out that after a terrible 2018 outbreak of gray leaf spot (on perennial ryegrass), 2019 was markedly better. “After the worst year ever in Ohio in 2018, it was very limited in 2019,” he says. “In fact, no confirmed cases on golf courses in Ohio.”

For an Upper Midwest perspective, we went to Dr. Paul Koch, an assistant professor at the University of Wisconsin. Koch also lists dollar spot as the main culprit this past year.

“Dollar spot pressure was our major disease in the Great Lakes region in 2019,” he says. “Pressure was moderate for the first part of the summer, but very high in August and September. Fall dollar spot has been increasingly problematic for superintendents. It was quite severe into the fall until cold temps in October finally shut it down.”

Gray leaf spot also started causing problems in Koch’s region. “Warmer summer temperatures in recent years have allowed this disease to move further north,” he says, “and for the first time we detected gray leaf spot in Wisconsin. The farthest north we had observed it prior to this year was Chicago.”

Dr. David McCall is an assistant professor at Virginia Tech. He considers 2019 a relatively calm disease year in the mountains of Virginia.

“Temperatures were above average in general,” he says, “but we had fairly mild rainfall and it was well-timed when we did receive it. This resulted in lower disease pressure on cool-season grasses during the summer months. However, it was much warmer than normal later into the fall, so we saw a lot of typical summer diseases in September and October. Our peak dollar spot flush is typically in August, but we didn’t see a peak until mid-September. This ultimately goes back to not being able to rely on a calendar to make applications.”

Finally, we spoke with a sales representative in the Pacific Northwest to get a feel for what disease pressure was like in that part of the country. Eric Thompson, who works for Simplot, is a former superintendent.

“Unusual, for us in western Washington, was the prevalence of dollar spot,” Thompson says. “Summer patch outbreaks were also higher than usual. The difficult thing with both of these pathogens is the fact that both develop in the spring with true symptoms showing in the summer.”

2020: A preview

What advice can experts offer in anticipation of disease in 2020?

In the Midwest, Koch warned about the emergence of gray leaf spot becoming a factor. “While this disease is not yet widespread in Wisconsin and other Great Lake states, continued warmer and more humid summers may cause it to become more severe and difficult to manage.”

McCall wasn’t too excited about looking into the crystal ball for disease pressure in the new year. “I don’t think we can make too many predictions for 2020 based on what we saw in 2019 alone,” he says. “The disease we will see in the upcoming year will ultimately boil down to what the weather is like at the time. Have a good plan in place going into the season but be open for modifications.”

In the Pacific Northwest, Thompson believes that superintendents, with the relatively new emergence of dollar spot and summer patch, need to now be prepared to deal with these possible visitors. “Careful monitoring of both weather conditions and soil temps can help with the severity of both pathogens,” he says.

Horvath had some advice for all superintendents as we move into the new year: “Ask yourself, What are the bits of information you have to access that tell you about what’s going on at your facility?” he says. “Are you monitoring moisture and recording it in some way? Are you monitoring soil and air temperatures? Be aware of how much precip you’re getting, and how much irrigation you’re putting down. And then look at all of those things to make an assessment about your environment and how conducive it is for a particular disease.

“Try to make your decisions before you see something happen,” he adds. “And be willing, even if you have a fungicide program in place, to make adjustments as you see changes to your environment occur.”

Butler agrees with Horvath. “The best thing any superintendent can do is to be aware of the diseases they are most likely to encounter, understand the weather parameters that promote those diseases, and plan their fungicide program for preventive applications instead of basing it on a calendar system,” he says. “Relying on a combination of historical data, current weather data and short-term forecast are the way to go.”