Although summer is when most turfgrass stress occurs, fall is when golf course superintendents need to keep their guards up and think about managing next year’s problems now. Rapid blight, snow mold, dollar spot and pythium root dysfunction can cause problems in the spring if precautionary measures aren’t taken now.
“Guys get into trouble because they take a beating in the summer and are afraid to lose grass,” says Frank Wong, a plant pathologist at the University of California, Riverside. “There’s lot of stress in summer, but it’s still an issue in the fall.”
Rapid blight
Rapid blight is appearing on annual bluegrass or Poa annua greens in Southern California this time of year, Wong says. Rapid blight also can be found in the low desert areas and Arizona on perennial ryegrass and rough bluegrass (Poa trivialis).
Rapid blight, which is common every year, is associated with high salt levels in soil when there’s a lack of rainfall or leaching. Salts are present in most irrigation water, and over time, they can accumulate in the soil profile.
The rapid blight organism is related to a marine lime mold that needs salt. In the fall, the disease often catches superintendents off guard. It’s suspected that with cooler weather, the combination of reduced irrigation and bluegrass being more biologically active can pull accumulated salts up through the soil profile, resulting in high salt levels in the upper soil surface, Wong says.
Aerification and sand topdressing, which are common fall practices, can make rapid blight worse if the pathogen is active. Research at Clemson University also suggests the pathogen grows best in the 75 to 80 degree range (Paul Peterson, Ph.D.). The combination of these factors is likely related to the increase of rapid blight in the fall.
As a preventative measure on greens, superintendents need to manage sodium levels, monitor salinity and flush appropriately, Wong says.
“According to Mary Olsen, Ph.D., at the University of Arizona, sodium is the main salt responsible for allowing rapid blight to develop, and anything you can do to reduce salinity in the soil profile will help,” he says.
Locations with poor water quality and/or greens with poor infiltration where salts can’t be leached have the most problems.
“If you already have rapid blight going into fall aerification, leach and apply fungicides before you aerify and topdress,” Wong says. “Going into the aerification period with all your ducks in a row is important.”
There are only three fungicides that control rapid blight, according to Wong: Compass (trifloxystrobin), Insignia (pyraclostrobin) and Fore (mancozeb).
“The problem is Fore is a contact fungicide and won’t cure the existing disease, but it will stop the spread of the next round,” he says. “Although Compass and Insignia have some systemic activity and have curative activity, they’re both QoI (Quinone outside inhibitor) fungicides. Since we’ve been using them over and over again for rapid blight control, I bet a doughnut and coffee that we’ll see resistance problems in the near future.”
Superintendents can see good results from fungicide applications as long as the salt levels are reduced. If salt isn’t managed, rapid blight will come back quickly as soon as the fungicides wear off, Wong says.
Brown ring patch
Superintendent and researchers in Southern California also are dealing with a new Rhizoctonia disease on annual bluegrass greens.
“We’re going to go with brown ring patch as common name,” Wong says. “We think it’s been around for a while, but it’s causing more damage recently.”
The disease thrives when temperatures are between 85 and 70 degrees, and more of it is coming back with cooler weather on annual bluegrass greens, Wong says. High moisture, a lot of organic matter and thatch accumulation, or other factors that cause a wet canopy, are environmental factors that contribute to brown ring patch. It’s most common in the fall, spring and early summer, and often recurs on the same greens. Anecdotally, greens high in thatch have more problems with the disease, Wong says.
Preventatively, management of canopy moisture is important, as is increasing sun exposure and air movement.
Curatively, many fungicides work well as long as they’re applied multiple times or watered down into the plant. Wong recommends an “HMO” approach in which ProStar (flutolanil) is applied first to see if that will control the disease. If not, then superintendents should move on to other materials such as Heritage (azoxystrobin), Insignia (pyraclostrobin), Endorse (polyoxin D), Medallion (fludioxonil), Chipco 26GT (iprodione) and Banner Maxx (propiconazole).
“It’s tough to knock out the disease entirely,” Wong says. “You can reduce the population down, but it will come back if the weather is right. The jury is still out on this one as far as best management practices.”
Snow mold
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Currently in the Midwest, there’s very low activity on bentgrass greens, says Joe Rimelspach, extension pathologist in the department of plant pathology at the Ohio State University. Temperatures are coming down and pythiums have passed. However, one thing superintendents want to gear up for is snow mold management, and several factors to be considered:
1. Applying fungicides.
2. Applying fertilizers to increase root growth, but not so much that it creates lush conditions that encourage snow-mold growth.
3. The duration of snow cover.
4. PCNB materials have been most effective against snow mold, but the EPA is going to restrict PCNB. It might be unavailable or completely lost.
“That will be a tremendous loss,” Rimelspach says. “PCNB is the standard for snow mold.”
Other products recommended in late fall include iprodione (Chipco 26GT, Iprodione Pro, 18 Plus) because they work well on pink snow mold, Rimelspach says.
Environmental conditions for snow mold are abundant moisture and cool temperatures. Snow mold is more prevalent on push-up greens than sand-based greens, and Poa annua is more susceptible to snow mold than bentgrass, Rimelspach says. Because turf is not growing in winter, recovery can be slower. Snow mold can be more susceptible in drainage patterns or spread via rollers or mowers.
In the Southwest, fusarium patch (also known as pink snow mold) caused by Microdochium nivale and dollar spot caused by Sclerotinia homeocarpa cause problems in the fall and winter. Both of these diseases can be controlled curatively using a variety of fungicides. In either case, once the average temperature drops below 62 F, the turf is slow to recover from any damage, making prevention more important, according to Larry Stowell, Ph.D., of PACE Turfgrass Research Institute. No recovery occurs when freezing temperatures are reached.
“That’s why a preventive application before temperatures drop too low is essential if there’s a history of either of these diseases in the fall or winter,” Stowell says.
Dollar spot
With dollar spot, the speculation is that the fungus colonizes in stolons and other plant tissues, Stowell says. It’s hanging around the plant or inside leaf of the plant. To suppress dollar spot, fall and spring fungicide applications can provide extended control. An application of Bayleton at 1 ounce per 1,000 square feet in the spring has been reported to provide 100 days of control, he says.
“When a fall fungicide application is used to prevent fusarium patch and the product(s) also have activity on dollar spot, combined with early spring preventive application, dollar spot can be effectively managed for even longer periods into the spring with less fungicide compared to curative control alone,” Stowell says.
Fall and spring fungicide applications for dollar spot when there are no symptoms in fairways can greatly reduce and delay that disease from occurring. In the fall, superintendents should apply fungicides six weeks before the temperature dip consistently into the 30s, Rimelsbach says.
“The timing is tricky,” he says. “If you can afford two applications, do one in the fall and one in the spring; but if you can only afford one application, do it in the spring.”
To suppress dollar spot, Rimelsbach recommends using systemic fungicides such as Cleary’s 3336 (thiophanate-methyl) T methyl Pro or Eagle (myclobutanil) and Bayleton (triademefon), Banner Maxx (propiconazole) and Emerald (boscalid), which works only on dollar spot.
Pythium root dysfunction
A disease that effects bentgrass greens in the transition zone is pythium root dysfunction.
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“It’s not the most common, but it has to be controlled preventively because it attacks the roots when the bentgrass is actively growing, preventing the grass from developing a deep and dense root system in the fall and spring,” says Lane Tredway, a plant pathologist and extension specialist at North Carolina State University.
Pythium root dysfunction occurs when soil temperatures are between 50 and 70 degrees. It develops in fall and spring and appears in summer. It doesn’t kill the plant out right but makes it more susceptible to stress.
“We’re just now developing an understanding the disease,” Tredway says. “It’s been documented only in North Carolina, South Carolina and Virginia. We think it’s more widespread, however, but it seems to be a Southern problem because it takes a lot of summer stress to make it active. The fungus could be in the North, but there’s not enough stress to induce symptoms.”
Those symptoms are circular patches two inches to two feet in diameter. The foliage will wilt and turn orange or yellow and die. The disease is attacking newly built bentgrass greens six to eight years after construction. After that, the disease tails off.
“I can only think of one or two new golf courses in North Carolina that haven’t had this problem with new greens,” Tredway says.
Pathologists and researchers still are working on recommended remedies to manage the disease.
“Right now, we suggest a rotation of Insignia (0.9 ounce) with a tank mix of Signature (4 ounces) and Banol (2 ounces) at 28 day intervals when soil temperatures are in the 50 to 70 degree range,” Tredway says.
Sound practices
In California, warm-season turf is boring compared to cool-season turf because there isn’t as much disease, Wong says.
“We’re seeing some spring dead spot on Bermudagrass, but it depends on how cold the winter is,” he says.
In Southern California, Bermudagrass is commonly used on fairways, but only low desert courses in Palm Springs and the Coachella Valley use it on greens.
“Those guys are on easy street compared to the guys that manage cool-season turfgrass greens in other parts of the state,” Wong says. “But it’s still important to go into the fall and winter dormancy period with healthy Bermudagrass that will quickly transition in the spring and summer.
For courses with creeping bentgrass greens, Wong says superintendents need to have a good preventive fall program to protect bentgrass root systems from take-all patch.
“Damaged root systems are likely to cause more problems under heat stress in the spring and summer,” he says. “Protecting them now is an investment for next year.”
Regardless of the turfgrass type, Wong says core aerification and sand topdressing are critical because they improve soil structure and remove organic matter.
“Guys who skip aerification now pay for it later,” he says.
Getting ready for the winter with sound fall practices is even more important since an El Nino year has been forecast for the West Coast.
“If it’s going to be wet and cold, I’m not going to have much of a vacation,” Wong says. GCN
