Image courtesy of Brandon Horvath: As damage becomes severe, entire plants are killed, and putting surfaces become uneven.

Superintendents better have their antennas up as forecasters predict a hot summer for most of the United States. Northern courses are in line to experience above normal temperatures, conditions ripe for Pythium.

So how can superintendents prevent Pythium diseases this year? Being proactive is, of course, the most important weapon to thwart Pythium diseases before they take hold of your turf.

Pythium is a dreaded and troublesome turf disease. Pythium is actually a complex group of many species, and as a group they cause foliar blights, crown rots or root rots across a broad range of temperatures. What they all have in common is their need for water. In fact, “water mold” is a common name for these organisms.

Hot, humid weather conditions, coupled with high surface or root moisture, make turf ripe for a Pythium invasion, says Dr. Brandon Horvath, assistant professor in the University of Tennessee’s Department of Turf Sciences. “Hot summer conditions with thunderstorms are one of the greatest concerns,” he says. “Superintendents should pay close attention to the daily and weekly weather forecasts to determine if they should protect themselves from a potential outbreak.” Typical conditions for disease development are daytime temperatures of 85 to 100 degrees and nighttime temperatures above 68 degrees.

Excessive nitrogen fertility, poor soil drainage and poor air movement contribute to the problem, says Dr. Rob Golembiewski, a Bayer Green Solutions Specialist. In turf, Pythium symptoms appear as sunken, greasy black patches and streaks on turf that can take on a reddish-orange to dark gray color. Affected turf is often matted and has a water-soaked appearance. White, cottony mycelium may be present in the early morning on affected areas, or after incubation of samples overnight in a moist chamber or plastic bag.

Vigilance is important, says Cam Copley, golf national accounts manager for Nufarm Americas. “Pythium can move rapidly and damage can be severe,” he says. “Misdiagnosing or a lack of awareness in these situations can be catastrophic.”

Measures to prevent an outbreak should be swift and comprehensive. Controlling moisture is one commonality when dealing with the different species, says PBI-Gordon product sales specialist James Goodrich. “Since Pythium is a water mold it makes sense to reduce or remove the water,” he says. “The environment for the disease is then less desirable for growth.”

Besides high temperatures and high humidity, poor drainage, highly compacted soils and overwatering are turf management issues that increase the chance of a Pythium outbreak, Goodrich says. Pythium is usually present in all soils, but if superintendents do things culturally to minimize a growing environment they can stay a step ahead of the disease.

“I don’t want to preach to the choir, but one of the best ways to get ahead of these diseases is to improve surface and subsurface drainage and really monitor the amount of irrigation you’re putting out,” he says. “So if you can reduce the water, you can minimize your chances of an outbreak.”

Good core cultivation, effective water management, and minimal nitrogen fertility give turf the best chance to resist a Pythium outbreak, says Kyle Miller, senior technical specialist for BASF Professional Turf and Ornamentals. “This still may not protect your turf, thus the reason for a properly timed preventive Pythium fungicide program during peak disease periods,” he adds.

While cultural practices are often disruptive to a course and its members, they are vital to mitigating outbreaks, Copley says.

Cultivation is key for preventing Pythium diseases, says North Carolina State University assistant professor and extension specialist of turfgrass pathology Dr. Jim Kerns. Pythium species require water to grow and spread. Therefore, irrigation management is paramount. For putting greens, it is essential to use a TDR meter to measure soil moisture. Keeping the putting greens as dry as possible can help prevent Pythium diseases. Sand topdressing is also critical, as it improves the surface characteristics and dilutes organic matter that naturally builds up in the system. Maintaining fertility programs is also key. “Pythium diseases are thought to be high-nitrogen diseases, but there are many Pythium diseases,” Kerns says. “Furthermore, high nitrogen typically refers to rates that are not reasonable for golf courses. Many times I find a little boost in nitrogen helps with most Pythium diseases. I am not advocating a half or one pound of nitrogen, rather an increase from 1/10 to 1/8 of a pound.”

Typical conditions for disease development are daytime temperatures of 85 to 100 degrees and nighttime temperatures above 68 degrees.
© Dr. jim Kerns

Root rot and root dysfunction develop when turfgrass is under stress. The single biggest stress is mowing, therefore adopting an alternating mowing and rolling program will help manage Pythium.

Pythium blight can kill turf in 24 to 48 hours, says Golembiewski, so preventive measures are key for controlling this disease. While fungicides are commonly used preventatively as environmental conditions turn favorable for Pythium development, proper cultural practices should be implemented to deter disease. He advises avoiding excessive nitrogen fertility; aerating/needle-tining to improve soil drainage and enhance air exchange; selective pruning of trees and shrubs; using fans to enhance air movement; and limiting dew duration.

“In turf areas most prone to Pythium outbreaks, delay mowing and/or rolling until surfaces are dry so as to not spread inoculums,” Golembiewski says.

Superintendents may want renovate low lying areas associated with sitting water or contours that create a flow of water across the surface, both of which contribute to Pythium outbreaks and movement across the playing surfaces.

“As for cost effectiveness, cultural practices should already be implemented as part of a good agronomic program,” Golembiewski says. “The key is to adjust when or how you implement to maximize their effectiveness in preventing Pythium outbreaks.”

Goodrich stresses proper fertilization and plant health. “In these days, fast green speeds, lower fertilization inputs (especially nitrogen), and decreased mowing heights can be problematic as they lead to weakened turf,” he says. “If you can bump up the nitrogen a bit and raise the mowing height a bit, you can help stave off the possibility of an outbreak. The practices I’ve mentioned are all things supers are doing or thinking about and therefore there is minimal cost above what they already have budgeted, so they can be very easy to implement.”

In addition, Syngenta technical manager Dr. Lane Tredway urges superintendents to “get ahead” of Pythium with a sound preventative fungicide program. “Curative control is not very effective, as most of these diseases attack at a time of year when the turf is not growing most actively,” he says.”

In growing environments conducive to Pythium development, more fungicide applications will be required to provide adequate control, Tredway says. A superintendent may need to apply higher rates at shorter intervals, or sometimes even mix multiple chemistries together.

Start preventative Pythium applications before conditions become optimum for an outbreak, Copley says. “There is a lot of truth to the old saying ‘an ounce of prevention is worth a pound of cure.’ The turf won’t have to deal with trying to heal itself and it will also be easier on the budgets of superintendents,” he says. “The preventative rate on products is sometimes one-half the cost of the curative rate.”

John Torsiello is a writer based in Torrington, Conn., and a frequent GCI contributor.