Bipolaris sorokiniana and Drechslera poae (Helminthosporium spp.)
Leaf spot and melting-out are two fungal diseases of turf grass within the “Helminthosporium” leaf, crown, and root disease complex. Leaf spot and melting-out are the most common and serious cool season turf grass diseases in N. America. Affected turf of both diseases show thinning of turf, irregular distribution across turf stand, and leaf spotting. When disease is severe, entire plants die.
Early symptoms of leaf spot are small, dark purple to black spots on the leaf blade. Oder lesions are round to oval spots with buff-colored centers surrounded by a dark brown to dark purple margin. The leaf spotting symptoms of melting-out on KBG are very similar to those of leaf spor; small dark lesions that develop into oval spots with buff centers and dark purplish-black margins on infected leaf blades. Colonization of the leaf sheath causes the leaf to turn yellow, then tan, and eventually drop from the plant. This stage is known as ‘melting-out’.
Leaf spot disease appears during cool, moist weather, in either spring or fall. The pathogen survives in leaf litter and debris and in infected plant tissue. A wet leaf surface is needed for the pathogen to germinate and infect. It is then spread by wind, rain, irrigation, and equipment. Infection can take place at any time that the soil is not frozen.
Melting-out disease is active during warmer weather. Under these conditions, severe turf loss occurs within 3 weeks. Cyclical periods of wetting and drying stimulate spore production. The pathogen is transported on infected leaf fragments that cling to shoes, mowers, and other equipment.
IPM METHODS :
- Balanced fertility—avoid over fertilization
- Water turf grass early in the morning and water deeply.
- Avoid frequent, short irrigation.
- Reduce thatch and remove clippings
- Use resistant cultivars in new plantings
- Apply broad spectrum fungicides every 14-21 days (or based on product label for targeting this pest).