Seize the disease

Features - Lawn Care

All you need to know to deal with early spring surprises in the lawn.

January 19, 2016

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The grass may not be growing, but what lies beneath could be active and setting up turfgrass for a tough spring start.

Many lawn diseases you manage in late first quarter have been manifesting since the previous fall. When the snow melts or the daffodils bloom, that’s when the damage is revealed.

In many cases, early spring lawn diseases can be prevented in fall with cultural practices like proper mowing, dethatching, mindful fertilization and even application of some fungicides. But since fall is over, and spring is on the way, now is the time to study up on common diseases you can expect to see this year and devise a plan for fast lawn recovery.

Lawn & Landscape spoke with turfgrass pathologists and diagnosticians who shared advice for identifying, preventing and treating diseases your clients’ lawns may suffer from this spring.

Spring dead spot
Photo courtesy of Nathan Walker

Prime conditions: This fungal disease actually “takes root” in fall as a soil-borne disease that impacts the roots, rhizomes and stolons of turfgrass. While it doesn’t spread as vigorously as some wind-borne diseases, a bout of spring dead spot can become an annual problem if it isn’t identified, mapped for preventive fungal treatment and managed by promoting healthy turfgrass growth during the warm season.

Because damage to turfgrass roots compromises its health, it’s more prone to cold damage, says Megan Kennelly, associate professor of plant pathology at Kansas State University.

Identify it: It leaves dead areas of grass about the diameter of a 5-gallon bucket, says Clint Waltz, professor and turfgrass extension specialist at University of Georgia. Bermudagrass is most impacted by the disease, but zoysiagrass is also affected.

Prevent it: Once you see spring dead spot, “the damage is done,” Kennelly says. And in Kansas, fungicides have been relatively ineffective in preventing this turfgrass disease.

However, other transition zone states (where this disease is common) find success with a preventive fungicide treatment.

Use the prior year’s spring dead spot damage as a guide for preventive fungicide applications. “Identify the area, map it and be prepared to treat in early fall,” Waltz says.

As for cultural practices, the best prevention is to select the proper cultivar and ensure good root health, Kennelly says.

“Choose a cultivar that is cold-hardy and has some disease resistance,” she says, adding that the dead spot occurs because fungus knocks down turf’s ability to stand up to cold temperatures in winter, resulting in dead spots in spring.

Turf can also benefit from aeration and verticutting to stimulate root growth, Kennelly adds.

Treat it: Fungicides with a number of active ingridients can be applied to prevent the spread of spring dead spot.

Contact your local/state resources to learn what has performed well in your area.

Large patch
Photo courtesy of Trugreen

Prime conditions: Large patch is a perennial problem on warm-season grasses before spring green-up, Waltz says. In fact, he says it’s the No. 1 early spring lawn concern in the southeast. Primary species impacted are zoysiagrass and centipede grass. “But that doesn’t mean that St. Augustine grass and Bermudagrass can’t get it, too,” he says.

In fact, spring 2015 was the first time in 15 years Waltz has seen large patch on Bermudagrass because of favorable environmental conditions. What triggers the disease? Excessive nitrogen in fall, poor soil drainage, over-irrigation, thatch accumulation and low mowing heights.

Identify it: You’ll notice circular patches that are yellow, tan or straw-brown. The patches range from 2 to 3 feet in diameter to as large as 8 feet across. Patches can grow together, forming diseased areas that are up to 20 feet large, Kennelly says.

Prevent it: “Large patch is active in spring and fall, and in this part of the transition zone (Kansas) we most commonly see it in springtime as turf is greening up,” Kennelly says.

Because this region tends to be drier than the southeast, fungicides should be applied in September.

“But the farther east you get with wetter, longer, muddy springs, they tend to require a spring fungicide application to get through that season,” she says.

Last year, Waltz advised clients to apply a fungicide by October and again in early to mid-spring.

The early spring fungicide application “can keep you from losing ground on recovery,” Waltz says.

Treat it: There are multiple active ingridients in fungicides that make for effective treatments. Contact your local/state resources to find out which ingredients are most effective. Improving drainage so turf areas can dry also helps.

You can also remedy large patch by avoiding early-season nitrogen applications in spring, Waltz says.

Also, maintain an appropriate mowing height (not too short) based on turfgrass variety. And for the first spring mowing, avoid a temptation to mow too low.

Winter desiccation
Photo courtesy of Peter Landschoot

Prime conditions: Brutally cold winters are tough on plants. Snow actually protects turfgrass, acting as an insulating blanket. So when you get frigid temperatures without the white stuff, winter desiccation is a real possibility. “If we lack snow cover, we’ll see more winter desiccation problems in the spring,” says Angela Madeiras, a diagnostician for turf, vegetables and ornamentals at UMass Plant Diagnostic Laboratory.

Identify it: You’ll spot large areas of dead grass, Madeiras says. “When patches of grass are exposed to cold wind with no snow cover, it’s more likely that turf can get killed by winter conditions,” she says.

Prevent it: Select a turfgrass that can stand up to bitter cold. “Bentgrass generally survives the winter better than bluegrass,” Madeiras says of some typical Northeast turfgrass varieties.

Beware of mowing too low in late fall before plants go dormant. A scalped lawn is more exposed and vulnerable during below-freezing temperatures.

Treat it: Reseeding in spring and a light nitrogen application will aid in recovery, Madeiras says.

Pink snow mold
Photo courtesy of Umass Turf Program

Prime conditions: Contrary to the disease name, you don’t need snow to get pink snow mold. Prolonged periods of cool, wet weather can trigger this disease, otherwise known as Microdochium patch.

“Pink snow mold can occur under snow cover, but really it just needs cool, wet weather, and in the Northeast while snow is melting we can have those conditions through March and April,” says Paul Koch, assistant professor in the department of plant pathology at University of Wisconsin – Madison.

Identify it: You’ll notice patches that are 2 inches to 1 foot in diameter, and brownish in color. On the outer edges, you might see fuzzy mycelium (the fungus) that is pinkish. Infected turf is generally matted down.

Prevent it: Avoid excessive fall fertilization, and mow into the fall. “Fungi like all that dead matter in thatch and will feed on that, so the more dead plant material there is, the happier fungus is in general,” Madieras says.

Treat it: Once the weather dries out turfgrass, this disease tends to fade as grass repairs itself. “You can use a fungicide to stop diseased areas from spreading in the spring,” Koch says.

Gray snow mold
Photo courtesy of Nathan Walker

Prime conditions: It requires at least 60 consecutive days of snow cover to develop. Koch says this disease is common in the Chicago area, northern Michigan, northern Ohio, lower New England and regions with similar winter conditions.

Identify it: Look for semi-circular gray or straw-colored patches that are a few inches to 3 feet in diameter. “Some patches can coalesce and cause big patches of dead grass,” Madieras says.

Longer grass looks matted down in diseased areas. “You may also see sclerotia, which are the nesting structures that the fungus forms,” Madieras says of the tiny, pea-like brown structures that are tightly packed fungal material.

Prevent it: Continue mowing into fall and avoid excessive fertilization.

Treat it: Treating gray snow mold is similar to pink snow mold – after the spring thaw and temperatures start to rise, turfgrass dries out and the disease may cure itself. You may use a fungicide to control disease spread. And dead areas can be repaired with reseeding and a light nitrogen application to promote new growth.

Koch says products with the active ingridients triticonazole plus pyraclostrobin, and azoxystrobin will provide control of snow mold.

Leaf spot
Photo courtesy of Nathan Walker

Prime conditions: On St. Augustine grass and Bermudagrass, the cool and wet weather in early spring can trigger leaf spot, Waltz says.

The disease strikes when weather is warmer but grass isn’t growing. It tends to fester in areas with heavy thatch, and in mismanaged turf.

Identify it: Leaf spot appears as small brown or black spots or flecks on turfgrass foliage.

Prevent it: “Avoid early-season nitrogen (in spring),” Waltz says, adding that dethatching the lawn in fall can also be helpful.

Treat it: “Many of the fungicides landscapers use are effective on leaf spot disease,” Waltz says.