Cool season grasses such as Kentucky bluegrass are particularly vulnerable to leaf spot and melting out disease. Leaf spot is present in virtually every lawn largely without consequence but extreme weather conditions with high moisture or improper lawn care practices may aggravate it and cause turf loss.
What to Look For:
Leaf spot first appears on grass blades as small brown or purplish spots and develops into larger spots with a dark colored border and tan center. As the fungus expands, it penetrates the leaf sheath and blades and causes multiple spots per blade which leads to leaf blight. If left untreated, the fungus can infect the crown and roots of the grass which causes them to rot. This stage is referred to as the “melting out” stage and may lead to large areas of damaged turf.
The spores of the casual fungus of leaf spot generally invade through mowing wounds and are the most active during cool, moist spring weather. The fungus survives through the winter and produces spores in the spring that cause spots on the newly growing grass. The fungus continues to produce spores through the spring that invade the crown and roots which contributes to melting out by the late spring or summer.
Spores only need to be exposed to moisture on a blade of grass for a few hours before it germinates and infects the blade. As the spores penetrate the leaf tissue, they kill cells and absorb nutrients and within a few days they can even produce more spores. Spores are especially present in lawn clippings.
Leaf Spot Control:
Scattered occurrences of leaf spot generally will not harm a lawn but the spreading of leaf spot caused by excessive moisture and improper mowing practices can lead to melting out and widespread turf loss. Using high nitrogen fertilizers in the spring also makes leaf spot worse. Following these practices should help keep leaf spot under control:
• Water early in the day and infrequently to avoid excess moisture
• Mow high and collect the clippings to avoid spreading spores
• Plant spore resistant cultivars in damaged spots
If you think leaf spot is infecting your lawn, don’t hesitate to contact us to assess your problem and provide a solution.
For more information about this and other lawn diseases, visit our disease prevention page.