Pithomyces chartarum in pasture, and measures for prevention of facial eczema

Abstract

Spores of Pithomyces chartarum (Berk. & Curt.) M. B. Ellis, (Dematiaceae), contain ‘sporidesmin’, a liver-damaging chemical. The fungus grows saprophytically on pasture debris, and is ingested by grazing sheep and cattle. Outbreaks of ‘facial eczema’, caused by the poison, occur if spore numbers in the pasture are greater than about 10 5/g dry weight of pasture. P. chartarum is not prominent in pasture in winter, spring, or early summer, but is a major constituent of the saprophytic flora in late summer and autumn. During this period, spells of warm rainy weather encourage growth and sporulation of the fungus, at times to the levels which render pasture dangerous for grazing. A warning service to farmers is operated by the New Zealand Department of Agriculture in the warmer districts where facial eczema occurs. Information on P. chartarum spore numbers through summer and autumn is obtained by regular spore trapping in sample pastures. When spore numbers have risen to levels approaching those known to be dangerous, warnings are issued if rain falls and the weather remains warm. Farmers are recommended to remove sheep and cattle from pasture during danger periods, and either to feed the animals with hay, or to graze them on crops of chou moellier, rape, or turnips grown especially for this purpose. Growth of P. chartarum in pasture has been held down to a safe level experimentally by combining irrigation with close grazing to reduce the amount of substrate available to the fungus. In other experimental work, thiabendazole sprayed on pasture has prevented the fungus from developing to a dangerous level.