When wet, humid weather persists for days, superintendents brace for Pythium root rot, a relentless soil-borne disease that appears in various climates and seasons and grows at an alarming rate.

Cool-season putting greens in the summer are particularly susceptible to Pythium root rot, says Dr. Jim Kerns, assistant professor and extension specialist of turfgrass pathology at North Carolina State University. Afternoon thunderstorms followed by several days of hot, dry weather provide perfect conditions for the disease, but it shows up in the event of limited rainfall if the air is humid enough.

“Typically, organic material favors the disease — any kind of wet, humid weather, most definitely,” Kerns says. “Typically, on creeping bentgrass and annual bluegrass, where it’s most prevalent, it’s usually associated with heat stress.”

When it comes to product applications to ward off Pythium root rot, Kerns says the PBI-Gordon fungicide Segway is “the king of the hill” because it has the broadest spectrum to fight against different Pythium root rot species, of which there are several. “It is what’s called a QII inhibitor, so it basically prevents the pathogen from developing energy,” he says. “It can’t make its own energy; the fungicide shuts that down.”

Once superintendents have performed soil tests and found that Pythium root rot is infecting their turf, they will want to make a preventative application of Segway in the spring and continue applications throughout the summer, says Jim Goodrich, PBI-Gordon product manager of fungicides, insecticides and plant growth regulators.

The hotbed for Pythium root rot is in the Transition Zone, Kerns says. In North ern areas, such as the Upper Great Lakes and New England, the disease is rare, but still an issue. And although the disease is most common on cool-season turf, it has been appearing lately on ultradwarf Bermudagrasses.

Warning signs include the formation of irregular dew patterns in the early morning, Kerns says. These signs indicate the disease has damaged the plant’s root, preventing the turf from taking up water. It leaves odd-shaped purple or purple-brown patches up to three inches in diameter, Kerns says. The diseased area can double the second day and triple the third. “It can move almost exponentially if those conditions are right, without some sort of protection there,” he says. “Then it can develop into large, irregular areas of essentially just dead turf.”

To culturally combat Pythium root rot, Kerns advises topdressing to increase infiltration rates and keep water out of the plant crowns. He recommends solid tining every two weeks in the summer and slightly increasing mowing heights and fertility rates.

Using a rotational program to control the disease, many superintendents prefer to make a Segway application first to ensure strong control; apply Segway as a preventative treatment at 0.9 fl. oz. per thousand square feet every 21 days, and rotate with other chemistries to control the disease to get it stopped before it has any chance to progress.

Segway not only treats Pythium root rot, but all Pythium diseases, Goodrich says. Pythium root rot can develop a resistance to Segway, so superintendents need to rotate, Kerns says. “This is an excellent chemistry, and we still do have to be very cognizant of preventing resistance development because we don’t really have anything as a viable alternative,” he says.

Segway is not approved for this use in all states. Contact your sales representative for more information.