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Scheduling Fungicide Applications for Pythium Root Rot in Cool-Season Turf // Background Pythium root rot (PRR) is a major problem on putting greens, and can be caused by over 20 different Pythium species that vary widely with host, geography, and optimum temperature for infection and pathogenicity. Pythium root rot is typically diagnosed as irregular chlorotic, yellow to orange patches or streaks, or thinned areas on cool-season turf in mid-summer, especially during periods of extended rainfall and high heat. It can also be a problem in water-logged soils in the spring or during periods of slower growth due to cooler temperatures. Pythium root rot is also problematic on slow-growing greens during overly wet months of winter and spring in the Pacific Northwest. // Preventative Control Once diagnosed on a specific turf area, PRR will likely be a perennial problem unless reconstruction, subsurface drainage installation, or other invasive measures are completed. University specialists agree that a preventative fungicide program designed for PRR is far more effective than occasional applications prior to forecasted wet weather. In areas where PRR is a chronic summer problem, preventative fungicide applications should start when 2” soil temperatures reach 60°F in the spring. Applications should be made in 1.5-2.0 gals water/1000 sq ft, watered-in with 0.1” of water, and made on 3 to 4 week intervals until summer heat increases. Then reduce application frequency to two-week intervals through the heat of the summer and return to 3 to 4 week intervals in the fall when soil temperatures cool. Preventative applications for PRR in the Pacific Northwest should start later in the fall when growth slows and rainy conditions persist. Spray schedules of PRR in the Pacific Northwest should be timed on 14 to 28 day intervals to coincide with applications for Microdochium patch. Bayer products for PRR include Signature ™ Xtra Stressgard ® and Banol ® , but it is important to rotate different modes of action like Segway ® in order to limit the development of fungicide resistance by Pythium spp. Table 1 lists recommended fungicide programs for preventative control of PRR. // Curative Control Though preventative control is always more effective than curative control, remedial control may be necessary during unusual weather conditions or the first time PRR is diagnosed on a golf course. Applications should begin immediately when symptoms are noticed, applied in 1.5-2.0 gals water/1000 sq ft, and watered-in with 0.1" of water. University specialists recommend the following strategy: // Terrazole ® 35WP (etridiazole) at 4 oz/1000 sq ft and watered in for the initial application // 3 to 5 days later an application of Segway ® at 0.9 oz/1000 sq ft. // 14 days later Banol at 2 fl oz/1000 sq ft plus Signature XTRA Stressgard at 4 oz/1000 sq ft // The preventative program in Table 1 can then be followed as guidance
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