Turf diseases don’t take a break. They are always there, ready to wreak havoc, especially come green-up time. Being aware of what happened to turfgrass the previous year and keeping a close eye on weather patterns the following spring and summer can go a long way in helping superintendents keep the bad actors away and maintain playing surfaces as pristine as possible.

The diseases that afflicted turfgrass in 2020 were a mixed bag, from dollar spot and Pythium root rot to fairy ring and brown patch, among others in the cast of nasty characters that were problematic to varying degrees during 2020.

Late-season dollar spot was prevalent in the Mid-Atlantic, says Dr. Michael Fidanza, professor of plant and soil science and director of the Center for the Agricultural Sciences and a Sustainable Environment at Pennsylvania State University/Berks Campus. Longer nights and lower sunlight angles keeping turf in shade were contributing factors to producing extended periods of leaf wetness and dew: “This environment is most favorable for dollar spot incidence, coupled with undernourished turfgrass, results in plant collapse and pitting common with dollar spot affected turf in mid- to late fall.”

USGA Green Section director of education Adam Moeller cited the following as 2020 disease concerns:
Take-all patch was active in the Midwest during the 2020 growing season.
© dr. paul koch

Dollar spot. Always an issue.

Pythium. More prevalent on courses that received untimely rain during July and August.

Brown patch. Always an issue but, perhaps, more so in 2020 due to increased humidity and untimely rain in southern portions of the Northeast.

Fairy ring. More problematic when courses are dry because the rings become hydrophobic.

The University of Wisconsin’s Dr. Paul Koch says dollar spot was “a little worse than average” across the Midwest in 2020.
© dr. paul koch

Take-all root rot on newly established bentgrass.

According to Dr. Paul Koch, an associate professor in the Department of Plant Pathology at the Molecular and Environmental Toxicology Center at the University of Wisconsin-Madison, dollar spot was “a little worse than average” across most of the Midwest due to prolonged stretches of warm nighttime conditions. “Daytime highs weren’t overly brutal, but those warm and humid nights are highly conducive for dollar spot and other foliar diseases to develop,” he says. “Take-all patch was really active across much of the region. It’s always tough to tell exactly why a disease like take-all is more severe in certain years, but the most likely contributors were a very wet fall in 2019 that contributed to increased fungal activity and huge temperature swings in fall 2019 and spring 2020 that made properly timing take-all fungicides difficult.”

Dr. Joseph Roberts, an assistant professor with the Turfgrass Pathology Horticulture Program Team in the Plant and Environmental Sciences Department Office of Clemson University’s Pee Dee Research & Education Center, explains that dollar spot can be an issue on both cool- and warm-season turfgrass. “Depending on the height of cut, dollar spot can become a significant issue that reduces both aesthetics and playability of close-cut surfaces like greens, fairways, and tees,” Roberts says. “We observed dollar spot in Bermudagrass roughs throughout much of 2020, but this is less of a problem as more disease can be tolerated in these areas.” In most cases, severe dollar spot outbreaks were linked to poor fertilization practices with low nitrogen coupled with high rainfall events that extended leaf wetness periods.

In the Southeast, issues that proved more significant than past years, Roberts says, included fairy ring — one of the worst years he has seen — and take-all root rot “mainly due to environmental pressure,” observed in 2020. Pythium presented foliar and root issues throughout the year. Heavy rain events in spring and fall resulted in multiple outbreaks on warm-season greens. “We also observed issues with Pythium root rot on creeping bentgrass in July during periods of extended high temperatures,” Roberts adds.

Brown patch (mostly on tall fescue) and dollar spot were the two main diseases observed on research golf turf by Dr. Cale Bigelow of the Department of Horticulture and Landscape Architecture, Turf Science, Management and Ecology at Purdue University. “Surprisingly due to the weather this year (a very cool spring and hot/juicy July) brown patch was more damaging than dollar spot during the summer, but dollar spot eventually did blight turf in our plots late in the season,” Bigelow says. “In the Indianapolis area it may have been slightly different as that area of the state was very dry for much of the year which would lend itself possibly to more dollar spot.”

Richard J. Buckley, director of the Plant Diagnostic Lab and Nematode Detection Service at the Ralph Geiger Turfgrass Education Center at Rutgers University, reports, according to a state climatologist, New Jersey had the second-warmest summer on record and the warmest July, and that led to issues with brown patch and Pythium blight in Poa annua on sand-amended native soils.

Dollar spot (shown here on fairway height bentgrass in eastern Pennsylvania) was prevalent late in the Mid-Atlantic growing season.
© Dr. Michael Fidanza

What about this year?

As for 2021, “only the weather knows what is in store,” Buckley says. “Our top five to 10 problems diagnosed get shuffled from year to year but are almost always confined to the usual suspects. They move up and down the list depending on the prevailing weather condition.

“It looks it could be a warmer and wetter winter for our area coming up, so I would expect to see a few samples of (pink snow mold), (yellow patch), and (brown ring patch) as we pass through the winter into spring,” Buckley adds. “We are always concerned with overwintering anthracnose infections in early spring and gray leaf spot (especially in tall fescue) in late-summer.”

Koch’s take on 2021 in the Midwest? “Dollar spot is always problematic, so I’m sure that will be again in 2021,” he says. “Take-all, fairy ring, summer patch and anthracnose are also common diseases throughout the Midwest and will likely cause problems across different parts of the region. Pythium root rot will likely be a problem in areas that experience heavy rainfall in the spring that saturate the soil.”

Dr. Brandon Horvath, a turf pathologist at the University of Tennessee’s Institute of Agriculture, urges superintendents maintaining warm-season turf to pay careful attention to spring weather so initial applications for take-all root rot, spring dead spot and large patch “get out at the right time, because there is inoculum being created this fall in areas that aren’t treated. That inoculum will increase disease pressure come spring.”

If Roberts “had to pick” diseases that will continue to be an issue in 2021, he believes take-all root rot certainly “has the potential” to continue its prevalence. “Some outbreaks can be linked to poor preventive maintenance practices, but I have also observed outbreaks at intensely managed areas with adequate preventive measures.”

Of course, Bigelow quips, “nobody has a crystal ball,” but due to the very prolonged dry conditions throughout much of the Midwest, any pathogen that might have a competitive edge on weakened turf would likely be a potential problem. “Especially pathogens that affect leaves which range from dollar spot, to red-thread to Microdochium patch,” Bigelow says. “Additionally, some (Kentucky bluegrass) areas may have symptoms associated with summer patch and that should be monitored.”

What can superintendents do to prepare for attacks on their course’s turf? “Always focus on agronomics and optimizing infrastructure and growing conditions first,” Buckley says. Cater inputs to the needs of your customers and individual course. There is a history of disease and insect pests, so plan a fungicide/insecticide program that reflects the historical record of your site.

“If one has a well-executed plan and the product in place (early order programs),” Buckley adds, “then it is easy to adjust if something comes up in mid-season.” Buckley recommends keeping an eye toward resistance management and remember “there are a bunch” of competent diagnostic that can help when things go wrong.

Koch says there are certain diseases like take-all patch and fairy ring where preventative fungicide applications are the only effective means for controlling them. For those who have seen take-all or fairy ring symptoms in the recent past, two or three preventative fungicide applications initiated when 2-inch soil temperatures reach 55 degrees for five consecutive days can be very effective at preventing symptoms. Predictive tools like the Smith-Kerns Dollar Spot Model can help superintendents time preventative dollar spot applications to effectively control disease without wasting product.

An accurate diagnosis to know what you are dealing with is the first step in developing a control measure, according to Roberts. “Many diseases cause similar symptoms,” he says. “A trained diagnostician can assist in identifying the cause of turfgrass loss, potentially saving money with proper control measures.”

Thatch management is important during the growing season as many of the pathogens we see thrive in excessive thatch. Regular cultivation and topdressing are critical to maintaining playing surfaces and also assist in reduce pathogen potential. And utilize resources from turfgrass research institutions when selecting products for a management program.

“Look closely at your fungicide program to make sure the most effective active ingredient is being used for a particularly troublesome disease,” Moeller says. “Combination products might have efficacy against a wide range of diseases, but the active ingredients might not be the most effective. The Chemical Control for Turfgrass Diseases 2020 edition developed by Rutgers, the University of Kentucky, and the University of Wisconsin is a fantastic resource that superintendents should review when building their control programs each year.”

Dr. Lee Miller, an extension turfgrass pathologist at the University of Missouri, says making prognostications with turfgrass — even in the immediate future — is difficult. “Forecasters often have trouble predicting weather patterns for the next week, much less six months ahead,” Miller adds. “This being said, even harsh winters don’t significantly alter the appearance of spring of summer disease outbreaks.”

While Miller said 2020 was a relatively uneventful year in terms of turf diseases, he saw scattered issues, such as Pythium root rot and fairy ring as well as the seemingly always present dollar spot. As for 2021, he says, spring showers bring May flowers and the same can be said for turf issues. This is especially true for soilborne diseases such as Pythium root rot, patch diseases and fairy ring. “Most spring-applied systemic fungicides should be watered in to target soilborne diseases, especially since they also do provide control of foliar diseases, like dollar spot, at the same time,” Miller says.

It’s also crucial to know soil conditions on greens. “Every once in a while, take a plug out and look and even smell what is going on in the soil,” Miller says. “You may find that in problematic areas water is not getting out of the soil profile, and there’s not a fungicide on Earth that can make bentgrass grow in a hot, waterlogged soil.”

John Torsiello is a Torrington, Connecticut-based writer and frequent Golf Course Industry contributor.