Effects of nitrogen and potassium fertilizer application on Drechslera spp. and Puccinia coronata on perennial ryegrass (Lolium perenne) foliage

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Abstract
In a field experiment nitrogen (N) fertilizer was applied to small plots of perennial ryegrass (Lolium perenne) at rates equivalent to 0, 200, 400 and 600 kg N/ha/yr at each of two levels of potassium (K) 0 and 200 kg K/ha/yr. Plots were cut at 6‐week intervals during 1977–79 and dry matter yield was determined. Water‐soluble carbohydrate and N content of the foliage were measured at three harvests in 1977. The incidence and severity of Drechslera spp. were assessed at and between harvests; attack by Puccinia coronata was assessed each autumn. Most foliar damage was caused by Drechslera spp. This was increased by N application which also altered the relative proportions of the Drechslera spp. present. K application had no apparent effect on disease incidence. Puccinia coronata was more prevalent on older leaves and on one occasion its incidence was increased by N application.