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Interrelationships Between Fertility and Red Thread Fungal Disease of Turfgrass. J. V. Cahill, Graduate Assistant, Department of Agronomy, University of Maryland, College Park 20742. J. J. Murray, Research Agronomist, and N. R. O’Neill, Research Plant Pathologist, USDA, ARS, Beltsville, MD 20705; and P. H. Dernoeden, Assistant Professor, Department of Agronomy, University of Maryland, College Park 20742. Plant Dis. 67:1080-1083. Accepted for publication 31 March 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1983. DOI: 10.1094/PD-67-1080.

In field plots treated with nitrogen (N), potash (K), and phosphorus (P), only 291 kg N/ha (highest rate of ammonium nitrate) in both 1980 and 1981 showed a significant (P = 0.05) reduction in severity of red thread foliar disease of perennial ryegrass (Lolium perenne) caused by Laetisaria fuciformis. Data in 1981 showed a significant (P=0.05) N × K interaction whereby disease severity was reduced using intermediate levels of nitrogen (194 kg N/ha) and potassium (135 kg K/ha). Significantly (P=0.05) lower disease severity ratings were observed in plots fertilized with 291 kg N/ha. Red thread disease severity was highest in plots treated with 98 kg N/ha (lowest rate used), regardless of the potassium level. Applications of phosphorus did not appear to affect disease severity. Tissue analysis showed a decrease in disease severity as potassium and nitrogen content increased in leaf tissue. Disease incidence and severity was higher in plots fertilized with the lowest level of nitrogen (98 kg N/ha) when foliar calcium content was low. At higher nitrogen levels (291 kg N/ha), disease severity increased with foliar calcium content. There was no apparent effect of phosphorus or potassium nutrition on turf quality. Best turf quality was achieved in plots receiving 291 kg N/ha; however, 194 kg N/ha produced acceptable turf quality for home lawns. Small amounts of nitrogen (24 and 49 kg N/ha) as single applications effectively reduced the severity of naturally occurring red thread disease within 1 mo of application, but turf treated with only hydrated lime and potassium showed no significant reduction in red thread disease.