Dollarspot Disease of Turf and Its Causal Organism, Sclerotinia Homoeocarpa N.SP.

SUMMARY The disease of fine turf known in America as “dollarspot” occurs in all parts of Great Britain but is less prevalent than some other turf diseases. The causal organism exists as several strains which maintain their respective characteristics under natural and cultural conditions. The strains differ in capacity for spore production; one yields ascospores and conidia, another ascospores only, and others reduced sporiferous structures only. The U.S.A. strain and an Australian strain, as also some British isolants, belong to the last‐mentioned group. The organism is characterized by well‐developed aerial mycelium, parts of which become reddish brown or cinnamon in colour; by sclerotial structures of parchment‐like thickness, in size from small flakes to expansive areas, olivaceous to black in colour; and by sporiferous structures arising from sclerotial sources. The ascigerous fructification is an apothecium which reaches full development with ascospores in spring; the conidiophore becomes cupulate and bears conidia toward autumn. The rate of growth of the strains and germination of spores is recorded for the range pH. 4–8. The optimum temperature for growth of British strains is 20–25° C, the minimum 0–1° C, and the maximum 35–37° C. The possible influence of temperature on the establishment of non‐sporing strains abroad is discussed. The organism is named Sclerotinia homoeocarpa, and a Latin diagnosis is given.