Killers in the cold

If an ounce of prevention equals a pound of cure, then lawn care operators would be well advised to try to prevent winter diseases rather than have to deal with the ugly aftermath when spring arrives. This is particularly true on high value turf like commercial and residential properties where a well-manicured lawn is desired.

It’s not always easy to treat a disease before it occurs, but if you’ve kept good mental and/or written record of your residential and commercial lawns, you should know what ailments might be on the way.

Pacific Northwest. The Pacific Northwest is a region of peaks and valleys and climatic differences that will keep an LCO on his toes. These differences can produce a variety of turfgrass diseases, according to Alec Kowalewski, assistant professor and turf specialist with the Department of Horticulture at Oregon State University.

Kowalewski says the LCO has somewhat of a balancing act between doing too little and doing too much when it comes to managing several diseases he sees in his region, which include snow mold, red thread, rust, dollar spot and leaf spot. Snow mold can be treated prior to the turf going dormant with demethylation inhibitors (DMI). Otherwise, he says not to exceed 1 pound of nitrogen per 1,000 square feet when doing late fall applications.

Too much nitrogen can stimulate growth and lead to instances of snow mold. He says snow mold develops in the Willamette Valley even in the absence of snow. He cautions against applying any fertilizer over the winter after the turf has gone dormant in areas where there is no snow cover.

Conversely, red thread, a disease that turns the leaf surface of perennial ryegrass red, can occur from a lack of nitrogen. If the LCO knows red thread may be a problem, they’re advised to fertilize with nitrogen in the late fall, before the turf goes dormant, at the rate of 1 pound per 1,000 square feet.

“You should have it in mind to do a fall fertilizer application to prevent rust and red thread and don’t fertilize over the winter to treat snow mold,” Kowalewski says.

Rust is a problem on Kentucky bluegrass in the region. The remedy for rust is to fertilize at the rate of 1 pound per 1,000 square feet.

“One of the most important cultural things a turf manager can do to decrease the severity of snow molds is to ensure the turf is completely hardened off going into the winter by avoiding excess fertility late into the fall.” John Inguagiato, assistant professor of turfgrass pathology at the University of Connecticut

“Nitrogen is a limiting factor in rust,” Kowalewski says.

Dollar spot, which is grouped into the category with red thread and rust, can also be controlled with a fall application of nitrogen.

On newer perennial ryegrass lawns, the occurrence of leaf spot can be an indication of lack of a fall application of nitrogen. Again, Kowalewski recommends an application of 1 pound of nitrogen per 1,000 square feet of turf. These applications can take place late into the fall in this region.

Southwest. As might be expected, turf and lawn diseases in the arid southwest are influenced by water, too much or the lack thereof.

Although Mother Nature is the culprit in a lot of winter turf diseases, LCOs in this region need to pay close attention to irrigation practices, according to Dr. David Kopec, extension specialist at the University of Arizona.

Winter brown blight occurs on overseeded bermudagrass that is seeded with perennial or annual ryegrass. Winter brown blight can occur on cold, wet soils that have been irrigated too much or drain poorly. Sometimes this is due to LCOs not switching from a germination schedule to maintenance schedule in their irrigation.

“Aerification at this time of the year is not advisable, rather, correct the irrigation clock,” suggests Kopec. Fungicides available that can be applied in the late fall include iprodione, vinclozalin, chlorothalonil, thiram and myclobutanil.

In the higher elevations in the west where Kentucky Bluegrass is the grass of choice, powdery mildew can actually cause death of the turf. It occurs in late fall in heavily shaded areas. Kopec says resistant cultivars are available. Fungicidal options include mancozeb and myclobutanil, myclobutanil, propiconazole, triadimefon and triticonazole.

Rapid blight, a relatively new disease, affects cool season grasses that are used to overseed bermudagrass in the early fall. It is most pronounced during periods of drought when salts don’t drain from soils.

“Turfs which use saline water or have saline soil with moderate soil sodium levels are most susceptible to this disease,” Kopec says.

Aerification can help only if it is done in conjunction with adequate rainfall or irrigation practices that will wash away salts during the summer months. Although rapid blight is not a fungus, there are two fungicides that can act as protectants: pyraclostrobin and mancozeb. These can be applied in late November.

Late fall might be a time when many LCOs are putting the tools and equipment away for the winter.

However, the season for fungal diseases on turf may be just getting underway. Making the right choices in cultural practices and chemical and fertilizer applications will ensure a nice greenup in the spring and a happy customer.

Midwest and Northeast. Lurking within the soil of lawns and turf are pathogens for different types of snow molds that will put an ugly face on a turf stand when spring arrives.

“Our primary concern in this region is snow mold,” says Loren Giesler, soybean and turf specialist at the University of Nebraska-Lincoln. “Once you’ve had it, you know it’s there. It has these great survival structures in the soil.”

He says snow mold is a particular problem where snow cover is very deep or it has been piled high and deep by snowplows and drifting. The freezing and thawing that occurs when the temperatures fluctuate between about 27 and 40 degrees is what really activates this fungal disease.

Some steps that can be taken that don’t require chemicals include erecting snow fences to contain snow drifts and spreading snow out during the course of plowing. Giesler also says there are fungicides that can be applied in late November in his region, before the turf goes dormant.

In the upper Midwest, near the Great Lakes, LCOs are likely to encounter three different types of snow mold: pink, gray and speckled. Planning to treat these fungal diseases is critical.

“The problem is it develops under snow cover, especially with speckled and pink snow mold,” says Paul Koch, assistant professor of plant pathology, at the University of Wisconsin-Madison.

“So if you don’t put down protection, it will be too late.”

He says snow mold will more likely be treated with fungicides if it is a high value lawn or turf, like golf courses, than home lawns.

The patchy spots you see in the spring as a result of snow mold will actually repair themselves with good cultural practices.

“Typically, most lawns don’t require snow mold protection because the grass species in lawns are a little more resistant to snow mold development, and when the disease does occur the turf usually recovers fairly quickly.”

Snow mold is also a persistent problem in the northeast, according to John Inguagiato, Assistant Professor, Turfgrass Pathology at the University of Connecticut. New Englanders also see occurrences of pink, speckled and gray snow mold.

Besides treatments with fungicides, there are several cultural practices that will help decrease the severity of snow mold.

“One of the most important cultural things a turf manager can do to decrease the severity of snow molds is to ensure the turf is completely hardened off going into the winter by avoiding excess fertility late into the fall,” Inguagiato says.

He adds that LCOs should also set the mower settings a little lower for that final cut of the season to remove leaf blades that can trap moisture, and to remove leaves and other debris before the snow flies.

South. Jim Kerns and his undergrads are busy at North Carolina State trialing fungicides to see which ones will be most effective on at least two maladies of lawns in the South: spring dead spot and large patch.

Kerns, a turf pathologist at NC State University, says LCOs need to monitor rainfall and soil temperatures this time of year.

A lot of rain and soil temperature hovering around 70 degrees is ideal breeding conditions for large patch, a fungus that colonizes in zoysia and bermudagrass.

“I always advocate for our LCOs to monitor soil temperature and rainfall in the fall,” Kerns says.

Spring dead spot is a more serious problem for the LCO as it kills the entire plant.

Unlike snow mold, which only kills the leaf blade and thus can repair itself in the spring, there is a sense of urgency in treating spring dead spot.

He adds it could be June or July before spring dead spot recovers, prompting fungicidal treatments, whereas large patch, especially on bermudagrass, may recover with the right aeration and fertility program. L&L