Seasonal changes in fungal spore numbers in ryegrass white clover pasture, and the effects of benomyl on pasture fungi

Abstract

Spore trapping and a herbage washing technique were used to follow seasonal changes of fungal spore numbers in ryegrass-white clover pasture from November (spring) 1968 to July (mid-winter) 1970. Spores of five parasitic fungi and of eight saprophytes were regularly counted. Numbers were highest in late summer and autumn, and were generally. similar in mown and grazed plots.

Numbers of crown rust (Puccinia coronata Corda) spores were greatest when pasture growth rate had fallen to its lowest summer level, and their peak preceded the peak numbers of spores of saprophytic fungi by about 2 weeks. It is concluded that ryegrass killed by crown rust is an important component of the pasture debris on which the saprophytes grew. The importance of clover pathogens in providing substrate for the saprophytes is less obvious.

In addition, the effects of benomyl on spore numbers were studied. The fungicide was sprayed on pasture according to recommendations for prevention of facial eczema disease of sheep. In benomyl plots spore populations of the fungi studied decreased, increased, or were unchanged as follows: Decreased: Cercospora zebrina Pass. Pithomyces chartarum (Berk. & Curt.) M. B. Ellis Cladosporium herbarum Link ex Fr. Cymadothea trifolii (Pers.) Wolf (1969) Increased: Alternaria tenuis Nees Stemphylium botryosum Wallr. Helminthosporium spp. (1969) No change: Puccinia coronata P. graminis Pers. Uromyces spp.Epicoccum purpurascens Ehrenb. ex Schlecht. Colletotrichum coccodes (Wallr.) HughesFusarium spp. Cymadothea trifolii (1970) Helminthosporium spp. (1970).

It is suggested that a fungicide that would control P. coronata and Pithomyces chartarum as effectively as benomyl controls P. chartarum would further reduce the risk of facial eczema disease of sheep.