Leaf Spot Diseases (Drechslera spp)

Diseases caused by Drechslera spp. were formerly classified as Helminthosporium leaf, crown, and root diseases. The fungus attacks cool season turfgrasses during the cool wet weather of spring and fall.

Drechslera leaf spot/melting-out symptoms initially appear as leaf spot lesions. The lesions initially appear as small purple colored dots. These lesions turn a gray to tan color with a dark purple to brown border. In the leaf spotting stage these diseases do not normally cause significant injury to the plant. However, as temperatures increase, infection may occur in the crown, stems, and roots where the plants eventually turn a straw colored and die. This is known as the melting-out phase of the disease.

The symptoms and conditions favorable for Drechslera spp are similar on all the turfgrass species listed below except for one – red leaf spot. Red leaf spot develops during hot dry weather of summer. This disease attacks primarily Agrostis capillaris (colonial bentgrass) but has been reported on some of the newer Agrostis stolonifera (creeping bentgrass) cultivars.

Cultural control

• Resistant cultivars, especially Poa pratensis (Kentucky bluegrass) cultivars are available that are resistant to Drechslera leaf spot/melting-out disease.

• Maintain adequate fertilization levels. Drechslera leaf spot/melting-out disease is associated with turf that is overly fertilized or not fertilized in the spring

• Mow at the higher end of the optimum cutting height for each turfgrass.

• Reduce the amount of thatch present.

 

Turfgrass Species                                   Drechslera species

Poa pratensis                                            Drechslera poae

Festuca spp.                                             Drechslera dictyoides

Lolium perenne                                         Drechslera siccans

Agrostis spp. (primarily A. capillaris)        Drechslera erythrospila