December 09, 2025

S3 E64 Grey Leaf Spot, Mowing Height, and Nitrogen

53 minutes

In this video, I review and break down one of the most referenced articles in cool-season turfgrass pathology: “Severity of Gray Leaf Spot in Perennial Ryegrass as Influenced by Mowing Height and Nitrogen Level” by Williams, Burrus, and Vincelli (2001).

This study investigated how two major management practices—mowing height and nitrogen rate—affect the intensity of gray leaf spot (Pyricularia grisea) epidemics in perennial ryegrass managed under golf-course conditions.

I walk through the methods, results, and implications of the research, and I discuss how the findings align—or don’t align—with common industry assumptions twenty years later.

🔬 Topics I cover in the review:

The study design and why the researchers chose fairway- and rough-height mowing

How N rates (0, 36.6, and 73.2 kg N ha⁻¹ per month) influenced GLS severity

Why mowing height had less effect on disease than expected

Environmental conditions that shaped the epidemic

What turf managers can actually take away from this paper

How these results compare to modern GLS observations in perennial ryegrass

💡 Why this article matters today:

Gray leaf spot remains one of the most destructive diseases of perennial ryegrass on golf courses. Understanding how cultural practices influence disease severity is still essential for developing integrated, evidence-based management programs. This paper is a cornerstone in that conversation—and it still sparks debate.

👇 Join the discussion:

Do you agree with how the authors interpreted their data?

Have you observed different mowing-height effects in your region?

Should N programs be modified during GLS-prone months?

Share your thoughts in the comments. Critical evaluation of research—new and old—is how we advance turfgrass science and avoid assumptions that fail in the field.

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By Travis Shaddox

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