Don't let it fall apart

Features - Disease Management

Summer might be over, but that doesn’t mean you should keep your guard down. We offer a region-by-region look at diseases that might surface this fall.

September 21, 2015
Rob Thomas

While the end of summer brings relief from oppressive heat to some and dread from the approaching snow to others, all superintendents must turn their focus to controlling potentially harmful fall diseases.

Based upon the summer we’ve had and the weather forecast, Dr. Jill Calabro, plant pathologist at Nufarm, says much of the country should know what to expect. Good news for most, but potentially mixed news out West.

“Most regions of the United States have had a mild summer overall, meaning that temperatures have not been as hot and oppressive as normal,” Calabro says. “The forecast for the remainder of the summer and in to fall, according to the National Oceanic and Atmospheric Administration, is for the drought in the West to continue, above average temperatures out West and along the Eastern seaboard and Gulf states, and slightly below average temperatures in the Midwest. That means it’s likely that the usual suspects of fall turf diseases will be out and about ... except out West.”

With relief on the horizon, other issues may present themselves to the parched West.

“Given the drought conditions, most diseases are not likely to be a concern,” Calabro says. “NOAA recently released a statement that an El Nino event is expected to continue into this fall and winter, and that this particular El Nino is predicted to be one of the strongest on record. This has the potential to impact the weather dramatically. During winter El Ninos, weather across the U.S. is historically milder, and the drought in California may be lessened. Milder conditions enable some fungal pathogens to persist throughout the winter, therefore, this fall it is especially important to be proactive in disease control programs.”

Patrick Gross, director of the West Region of the USGA Green Section, says rapid blight and summer patch are a concern during the late summer/early fall on Poa annua greens, especially in areas with saline soil and water conditions.

Courses that overseed their Bermudagrass with perennial ryegrass, such as those in Palm Springs, Phoenix, Tucson and Las Vegas, have to be wary of pythium blight. According to Gross, most courses already treat preventively in conjunction with their overseeding program.

Dr. Kathie Kalmowitz, technical specialist, BASF Turf and Ornamentals, looked at issues related to overseeding, as well.

“For the Far West Arizona and California, the drought may make for a difficult rapid blight overseeding season,” Kalmowitz says. “In areas of California where greater rainfall events occurred, the soil profile may have been flushed of salts and the Poa-bentgrass greens may not be as susceptible this season. However, for those courses in Southern California and Arizona that overseed, the extended drought means the rapid blight season will be difficult.”

The West’s diverse topography and myriad climates presents unique challenges, according to Gross. “Courses with Poa annua greens along the Pacific coast with a cool, moist climate are on the lookout for michrodochium patch/pink snow mold throughout the fall and winter,” he says. “Many treat preventively when daytime temperatures are consistently between 50-65 degrees Fahrenheit.” Courses in the high elevation mountains treat greens preventively for gray snow mold in the fall as they blow out their irrigation systems and prepare for winter, Gross adds.

Derek Settle, technical specialist on the Bayer Green Solutions Team, has his eye on large patch prevention, which begins as soon as soil temperatures cool. “This pathogen, R. solani AG LP, is driven by saturated soil conditions and cool temperatures in the fall and spring,” Settle says. “When cool, wet conditions prevail, this is an aggressive disease on most warm-season turf.”

“The weather-based model that is used relies on average soil temp at 2 inches depth,” he adds. “When we drop to between 72-75 Fahrenheit, the first app begins. Typically two fall apps are required for good control. A third spring app will provide near blemish-free control.”

Calabro echoed Settle’s concern over large patch and added spring dead spot and take-all patch to the watch list.

“For all of these diseases, a preventive approach to disease management is the best,” she says. “For spring dead spot (on Bermudagrass) and zoysia patch (on zoysiagrass), fall applications are far more effective than spring applications. Target applications for spring dead spot during wet weather with daily temperatures below 60 Fahrenheit. Large patch favors sites with a high level of thatch and becomes active when soil temperatures fall below 65 Fahrenheit.”

The Southeastern states see more rainfall than the Southwest in general, but late summer often ramps up precipitation, which will affect a superintendent’s approach.

“If there is a strong tropical season in the Southeast, many courses may see fairy ring problems again coming back for the fall if greens are low in fertility and if a greater thatch layer has developed,” Kalmowitz says. “Getting ahead of rings just as you observe the signs will help with quicker healing. If you see rings or mushrooms, check to determine where the infection is occurring – how deep and how extensive by taking some profile samples. This helps you make a better fungicide application with the spray volume that gets down into these hydrophobic areas.”

Extreme heat in July won’t help heading into fall, either. Kalmowitz says high temperatures were stressful to courses with bentgrass greens, fearing some turfgrass may have been lost. Rhizoctonia solani and large patch aren’t unique to the Southwest, according to Kalmowitz.

“The Transition Zone South – those courses with zoysia or seashore paspalum – will need to be thinking about their applications (two in the fall, possibly more for Florida and Texas if wet and warm) for large patch caused by Rhizoctonia solani,” she says. “If the weather remains warm and dry, then at least the first application into September should be planned, and additional application(s) later in the fall or in early spring right at green-up should be anticipated. For those areas of the South where the seashore paspalum will not be going dormant, then the late fall/winter applications will be necessary.”

With that said, the paramount concern for the Transition Zone this fall is spring dead spot. “Those who have converted in the last couple of years to the ultradwarfs Bermudagrass after this last winter should protect from spring dead spot, especially if they are in areas that are more susceptible to winterkill from the lower temperatures,” Kalmowitz says. “Greens are not the only areas that may need protection, since north-facing slope areas on fairways are highly susceptible and other history area on fairways/roughs where the course has had prior problems.”

“With the drop in evening temperatures, dollar spot will come back into some bentgrass greens,” she adds. “Dollar spot prevention in the fall for the Transition Zone bentgrass is essential. A couple of preventative applications with a broad spectrum product continues to control the brown patch but also controls the dollar spot.”

Settle says spring dead spot prevention parallels the timing for large patch prevention, but an exact temperature model isn’t needed. Instead, at fall’s start superintendents will put out two applications timed a month apart. The fungicides used are always at the high label rate and must be watered in to get contact into the root zone. A harsh winter and this disease can have devastating effects on Bermudagrass from tee to green.

“Two fungal pathogens responsible, Ophioshaerella korrae and O. herpotrica, are root rotters,” Settle says. “What’s interesting is that a cold winter is also needed. This is the primary disease of Bermudagrass in the Transition Zone where cold winters can occur. The disease gets really bad if a harsh winter occurs, equaling winterkill of Bermudagrass. We’ve had a string of those kinds of winters as of late in the Midwest and Southeast, so spring dead spot has been a big problem wherever Bermudagrass is grown in areas where turf dormancy occurs. For ultradwarf Bermudagrass greens, newer fungicides will offer good to excellent control.”

Zac Reicher, technical specialist on the Bayer Green Solutions Team, carefully monitors from Indianapolis to Seattle and is watching for dollar spot, which can be nasty if the northern part of the country has a prolonged warm fall. Snow mold also is a major concern.

“If left unchecked, it can kill 100 percent of the turf in the spring,” Reicher warns of snow mold, adding that many superintendents are currently repairing areas affected by summer stresses. “A lot of guys are installing new turf and new seedlings are much more vulnerable.”

To control snow mold, Reicher suggests superintendents continue mowing until the grass stops growing in the fall. If it gets too high, it “flops over” and creates humid spots where snow mold can thrive. He also recommends continued spoon feeding nitrogen or moderate nitrogen fertilization programs into the fall, but to avoid heavy rates of nitrogen mid-fall, as it may limit hardening off.

Limiting snow collection and improving drainage on susceptible areas also helps. Lastly, fungicides should be applied in the late fall. “Some will require multiple applications, especially if heavy rain occurs after application and/or extended snow cover is present,” Reicher says. “Combinations of active ingredients produce the best control of both pink and gray snow molds.”

Gary Myers, CGCS, BASF project leader at Pinehurst, also has dollar spot on his fall radar.

“The No. 1 concern for the Midwest and Northeast regions will be dollar spot control,” Myers says. “Dollar spot can be active late into the fall and damage from dollar spot can be evident throughout the winter if preventative applications are not applied. A couple of preventative long-lasting applications with a broad spectrum product will control dollar spot late into the fall. There are several products on the market that will give control of dollar spot for 21-28 days and these products are perfect since most superintendents are not spraying on a 14-day rotation anymore.”

For courses in the upper Midwest and Northeast, winter damage is always a concern, Myers adds.

“Proper timing of snow mold applications with several products that have different active ingredients and are from different classes of chemistry is very important,” he says. “Those courses that sustained considerable winter damage on fairways may consider a blanket application or at least target spraying where winter damage was most prolific. Golf courses in the Midwest have been experiencing excessive rainfall early in the summer with drier conditions that followed. This could lead to shallow root systems leading into the fall months. Agronomic practices will be essential this fall such as aerification, fertilization and topdressing.”

Rob Thomas is a Cleveland-based writer and frequent GCI contributor.

Weeding out problems
We aren’t forgetting about the other problems your turf might encounter this fall.

In addition to this disease guide, we are offering a region-by-region fall weed and pest breakdown. Tips and updates from multiple experts, including researchers, technical specialists and USGA Green Section agronomists, can be found by entering into your web browser.