Pithomyces chartarum spore counts in pasture

Abstract

Pithomyces chartarum spores in pasture leaf samples were counted by a wash method, and their numbers related to rainfall and grass minimum temperatures at the sampling site or to site topography. There was no evidence that factors other than humidity and heat input into pasture affected the growth of P. chartarum. There was some correlation between spore numbers and the rainfall and grass minimum temperatures of the previous 3 days, but the correlation was not good enough to make the meteorological observations alone a satisfactory basis for a facial eczema warning system. Spore numbers often did not rise during the warm moist periods indicated by rainfall and grass minimum temperatures, and sometimes reached their peak or remained at dangerous levels for some time after grass minimum temperatures had dropped after such periods. Site topography appeared to affect spore numbers principally in the way it affected heat input. There were more spores on pasture sheltered by hedges than at unsheltered sites, and more on north- and west-facing slopes than on those sloping to the east. There was no evidence that spore numbers differed between adjacent and similar paddocks, but there was too great a difference between those on two farms 8 km apart on a flood plain to make spore counts on the one more than generally useful on the other. As far as could be judged, farmer action taken on warnings based on counts made at scattered points in a district reduced the incidence of clinical facial eczema, but to eliminate the disease it would be necessary to make spore counts on each farm, particularly in areas of extensive farming on hill country.