Leaf Spot

Disease Background

Drechslera spp.

Leaf spot diseases in the UK are primarily caused by Dreschelera spp. Leaf spot is a fungal disease, which affects cool season grasses, including perennial ryegrass (Lolium perenne) and brown- top bent (Agrostis capillaris). Leaf spot is most prevalent during warm, humid conditions. The spores are dispersed through rainfall/ irrigation and the extent of the severity of infection will depend upon the virulence of the fungus and the susceptibility of the grass plant. Leaf Spot in the UK must not be confused with Gray Leaf Spot (Pyricularia grisea), a disease which is found on both warm and cool season grasses in the USA.


The significance of disease tolerance in grass breeding

There are significant differences in tolerance to leaf spot between individual cultivars within a species. Cultivar selections from the breeding programme are inoculated with leaf spot, both in the laboratory climate rooms and in field trials. In addition, leaf spot is allowed to occur naturally in field trials in order to achieve a comprehensive picture of a particular cultivar’s tolerance. Graph 1 shows the tolerance of cultivars of perennial ryegrass in a combined shade and wear stress situation. The severity of leaf spot attack was amplified in these conditions in comparison with identical trials outside the shade and wear trial tent.