Tips to best manage Pythium blight

Early signs of Pythium blight include yellowish or brown spots ranging from the size of a quarter up to 6 inches in diameter. (Photo: PBI-Gordon)

Pythium blight is one of the most common diseases of turfgrass. To prevent it from establishing and spreading, experts say lawn care operators (LCOs) must manage the disease properly. Brian Aynardi, Ph.D., Northeast research scientist for PBI-Gordon, and James Lee, category manager for SiteOne, share chemical and cultural control techniques for LCOs to deploy to best manage Pythium blight.

Chemical control

“There are few effective control options that can provide satisfactory control of Pythium blight,” says Aynardi. “Products containing cyazofamid as the active ingredient are the most effective for controlling Pythium blight, and a good rotation partner to cyazofamid is the active ingredient mefenoxam or the strobilurin fungicide azoxystrobin.”

Lee says pros should be aware of the environmental conditions that Pythium blight favors to best deploy chemical control strategies. In addition, once an area has been infected by Pythium blight, turfgrass managers should develop an annual preventive maintenance program.

“Without a good preventative plan in place, Pythium blight can spread and cause damage to turfgrass within 24 to 48 hours and require an immense amount of costly repair work,” he says.

Experts say having a good preventive plan is the best approach. When the conditions are most conducive for Pythium blight to occur, pros should apply preventive fungicides. If the prevalent turfgrass is susceptible to Pythium blight — such as perennial ryegrass — and the environmental conditions are conducive, it is necessary to apply a preventive fungicide. Conditions such as high leaf moisture and relative humidity greater than 90 percent favor disease development.

“There is no such thing as an acceptable disease level with Pythium blight because once the pathogen infects turfgrass, the disease will spread rapidly, resulting in significant turfgrass loss,” Aynardi says.

Cultural controls

Experts say LCOs should have a good understanding of how Pythium blight infests to achieve good disease management with cultural practices.

“Pythium blight may develop if the pathogen is present in waterlogged soil, air circulation is poor and air temperatures are favorable for the disease,” says Lee.

Pruning nearby trees and bushes will increase the amount of sunlight and air movement, which will reduce the amount of moisture within the turfgrass and prevent disease development.

“Pros should reduce the use of quick-release nitrogen on newly seeded perennial ryegrass during periods when Pythium blight is prevalent,” Aynardi says.

Lee adds that in addition to improving air circulation, pros should deploy cultural methods such as ensuring proper drainage, amending soil and changing the grade of the ground’s slope.

What to avoid

Not recognizing the onset of Pythium blight and how it can be easily spread is a common mistake, says Lee.

“Pythium blight mycelium on top of turfgrass will look like loose cotton spread across the turf that can be confused with spider webbing,” he says.

When turfgrass managers mow wet Pythium blight-infected turf, tires can spread the disease to other turfgrass areas. LCOs should avoid spreading the pathogen through any form of movement, including water runoff, foot traffic or tire tracks before it is too late.

“Turfgrass managers should be aware that curative applications of fungicide will not provide much benefit when applied to symptomatic or dying turfgrass,” Aynardi says.