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How to ID Pythium blight

August 2, 2021 -  By
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Pythium blight (Photo: PBI-Gordon Corp.)

Loss of turf Areas impacted by Pythium blight will exhibit major turf loss and a bronze color. (Photo: PBI-Gordon Corp.)

Knowing how to prevent, properly identify and manage
Pythium blight will determine how big of an issue this disease can become.

What to look for

While Pythium blight can occur on any type of turfgrass, it’s especially problematic on new stands of perennial ryegrass and annual bluegrass, says Brian Aynardi, Ph.D., northeast research scientist at PBI-Gordon Corp. It can affect cool- or warm-season turf, though tall fescue and Kentucky bluegrass are typically less affected.

Characteristics include yellowish or brownish spots about the size of a quarter that grow up to 6 inches in diameter, says Brent Radford, golf, turf, landscape and nursery agronomist with Wilbur-Ellis Agribusiness. If Pythium blight is allowed to persist, the disease will cause significant areas of turf loss, giving the dead turf a bronze appearance.

“When daytime temperatures are above 85 degrees Fahrenheit, nighttime temperatures are above 65 degrees F and 90 percent relative humidity persists, Pythium blight has a potential to develop,” Aynardi says. “Proper identification at the time symptoms and signs (mycelia) are present is critical since the disease spreads rapidly.”

The disease is often misidentified as brown patch or dollar spot. Symptoms may disappear by midday, making identification more difficult, says Ben Pease, turfgrass agronomist for The Andersons Plant Nutrient Group.

“Look for cottonlike, white mycelia that appear in the early morning around the edges of and within the disease patch,” Pease says.

Best course of action

Several cultural practices can help prevent the pathogen from causing infection: maintaining canopy height, increasing air movement in prone areas by pruning trees and shrubs, improving drainage, using a turf species that’s less affected and increasing sun exposure. Aerating also allows more oxygen to reach into the soil and creates a way for water to get to the roots — which pays dividends in preventing Pythium blight, Radford says.

“However, sometimes the use of a fungicide may be warranted, and there are products labeled for use on commercial and residential lawns, such as cyazofamid and azoxystrobin,” Aynardi says.

There’s often a reluctance to use a fungicide due to cost or lack of information about the products that may be used, especially in residential settings, Aynardi says, but once Pythium blight kills the turf, it won’t recover, and the area will need to be reseeded.

“If in doubt, consider contacting a distributor rep or chemical manufacturer about using fungicides and communicate to the client that reseeding will be a more expensive proposition,” Aynardi says.

Common mistakes to avoid

Applying the incorrect amount of fertilizer can cause thatch, which can hold moisture and lead to Pythium. Operators can ensure they don’t overfertilize by using a slow-release fertilizer, Radford says.

“The technology releases nitrogen over three to four months, versus releasing all of the nitrogen within a few weeks,” Radford says. “We see fewer disease problems because it meters out the nitrogen.”

Seeding during the summer also can cause Pythium blight because the heat and frequent watering during the establishment period are the perfect mixture for development.

“Since seedlings are much more susceptible to Pythium than mature turfgrass stands, we recommend seeding in September once temperatures have decreased,” Pease says.

The lower the mowing height, the higher the possibility is of having Pythium blight and other diseases, as well. Lawn care operators also should avoid watering during the hottest parts of the day.

Pythium is there all of the time,” Radford says. “It’s just a matter of creating a vector or wound that gets it started.”

Sarah Webb

About the Author:

Sarah Webb is Landscape Management's managing editor. She holds a bachelor’s degree from Wittenberg University, where she studied journalism and Spanish. Prior to her role at LM, Sarah was an intern for Cleveland Magazine and a writing tutor. She can be reached at swebb@northcoastmedia.net.

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