Many golf course superintendents have battled an unknown disease of new creeping bentgrass putting greens over the last few years. This disease has been referred to as “summer crown rot”. However, as many of you know, we have had a difficult time finding the pathogen that causes this disease.
Two golf courses in the Raleigh, NC area observed mild symptoms of this unknown disease in the fall and spring during relatively cool weather. One case occurred in November 2003 and another in March 2004. The symptoms seemed to be induced by stress – low nitrogen, close mowing, drought stress, etc. – much like in the summer.
When looking at samples from these fall and spring cases, we observed a Pythium species causing significant damage to the new root growth. Last fall, we identified the suspected pathogen as Pythium volutum. We have not yet identified the isolates collected this spring. Our current theory is that this disease is caused by a Pythium that does most of its damage in the fall and spring during cool temperatures. The symptoms do not appear until summer when stress from heat and drought overwhelms the infected turf.
If our theory is correct, then spring and fall will likely be the best time to control this disease. For superintendents in the Southeast who have had severe cases of this disease, I recommend initiating a preventative Pythium program immediately. Those in the Northeast and Mid-Atlantic can probably wait until bentgrass root growth begins this spring.
We have shown that the following fungicide treatments are effective for curative control of this disease:
- Subdue Maxx (1 fl oz, not watered in)
- Chipco Signature (4 oz, not watered in)
- Terrazole 35WP (3.25 oz, watered in with 1/8")
- Heritage 50WG + 3336 50WP (0.4 + 8 oz, watered in with 1/8")
Equivalent products containing the same active ingredients will perform similarly. Of these treatments, the true Pythium fungicides have proven most effective. Heritage + 3336 was only moderately effective on a curative basis, so I would not suggest using this mixture for preventative control.
After symptoms of this disease appear, we have found that the following program is most effective:
- Heritage 50WG + 3336 50WP (0.4 + 8 oz, watered in with 1/8")
- Terrazole 35WP (3.25 oz, watered in with 1/8")
- Subdue Maxx + Nitrogen (1 fl oz + 1/8 lb, not watered in)
These treatments are typically applied 3 to 5 days apart, and have been shown to provide up to 3 weeks of disease suppression.
Proper cultural practices appear to be very important for managing this disease. Low nitrogen fertility, close mowing, drought stress, and infrequent aerification seem to encourage this disease. Any other factors that reduce root growth in the fall and spring, or increase the amount of stress on the turf during the summer, will likely encourage the disease.
Source: North Carolina State University
