Leaf Spot Diseases
Red leaf spot of bentgrass.
These diseases are extremely common and in fact, occur on all turfgrasses. They are, however, generally not so severe as to warrant control and many will go unnoticed.
They are caused by any of a number of fungi which generally fall in to one of the following genera: Drechslera, Bipolaris, Curvularia or Exserohilum. In the UK and Ireland, leaf spot diseases caused by Drechslera spp. are the most common and red leaf spot of bentgrass (caused by D. erythrospila) is arguably the most damaging of fine turf.
Diseases caused by Drechslera spp. are some of the turf diseases which used to be grouped together as Helminthosporium leaf, crown and root diseases. This term is no longer commonly used but we refer now to the specific fungus that causes leaf spot symptoms on specific turfgrass plants.
The leaf spot diseases with which we are likely to be affected on cool-season grasses, are most prevalent under warm, humid conditions. The spores of these fungi are disseminated by rainfall / irrigation and regular rewetting of a dry thatch will encourage spore production by these fungi.
All leaf spot fungi will cause some type of leaf spot on the affected plants. The extent and severity of the leaf spot will depend on the virulence* of the fungus and the relative susceptibility of the plant.
Some of these leaf spot fungi can also damage the crown and roots of the turfgrass plants and may lead to symptoms of complete plant loss which are termed 'melting out'.
*Virulence The degree of pathogenicity of any given pathogen. An indication of its ability to cause disease.