Ecology of the fungusPithomyces chartarum(Berk. & Curt.) M. B. Ellis in pasture in relation to facial eczema disease of sheep

Abstract

Pithomyces chartarum (Berk. & Curt.) M. B. Ellis (syn. Sporidesmium bakeri, Syd.) was found saprophytic on dead material of pasture plants. Optimum temperatures in the laboratory were mid-upper seventies °f (about 24°c), and main development of the fungus was in summer and autumn, usually when temperatures in earth at 4 in. were about 65°F (18°c), or higher. In the field, rain was necessary for infection periods. Sporulation occurred with rain, and less freely with dew. In the field, incubation periods, from infection of substrate till sporulation, were usually 4 or 5 days during summer and autumn, but could be 3 days. Development of P. chartarum in the field was related to seasonal pattern of growth of perennial ryegrass. Death of grass in midsummer, and after seed ripening, was a major source of debris for strong development of the fungus early in autumn. Another major debris source, death of leaves due to shading in tall swards, supported strong growth of the fungus in late autumn after autumn flush growth of grass. Other classes of debris, for example, those arising from mowing, or from attack of plants by insects or fungi, augmented development of the fungus. Significance to facial eczema is discussed. The correlation, found by other workers, of facial eczema with large numbers of P. chartarum spores in pasture, indicates that pasture containing a large amount of plant debris at those times in summer and autumn when rainfall and temperature are most suitable for development of the fungus will bring on the disease. It is suggested that risk of facial eczema will be diminished with reduction of the amount of plant debris by reducing grass flowering, increasing summer survival of grasses, preventing leaf death due to shading in tall swards, controlling pasture pests and diseases, avoiding mowing, and eliminating undesirable species such as Yorkshire fog.