In recent weeks, many homeowners have begun to see straw-brown patches appearing in their lawns. These patches often appeared very quickly – almost overnight it seems. So what’s the problem? In many cases, it’s a disease called Ascochyta leaf blight.
Ascochyta leaf blight is a fungal foliage disease most commonly affecting Kentucky bluegrass, although perennial ryegrass and tall fescue can be affected. In years past, Ascochyta was thought to be a minor pathogen but is appearing more frequently in Nebraska lawns.
Fortunately, this disease only damages leaf blades while the crown or growing point of the plants and their roots are not affected. This allows plants to produce new leaves and grow out of the damage almost as quickly as it appeared.
Typical symptoms include irregular straw-colored patches that appear very quickly. Severely infected grass blades are killed from the tip all the way down to the crown, causing the grass to appear dead. But although the grass appears completely dead from a distance, closer inspection shows the leaf blades are only dead about one-third down the length of the blade. Leaves show a straw-colored tip dieback, an abrupt margin between dead and healthy tissue, and a reddish- brown border at the base of the dead section.
Infected leaves may also show red-brown leaf spots, a fish-hook tip on totally dead leaf blades, or a needle-point dead tip on partially dead leaf blades.
Large areas of uniformly blighted grass are common, although a scattered patchy appearance to the damage is also common. In some cases, homeowners find streaks of damage following their typical mowing or fertilization pattern leading them to believe they have some type of chemical damage.
Nebraska Extension turf specialist Bill Kreuser says, “It’s commonly thought that mowing spreads the disease, but that is not the case. Instead, the physical traffic and weight of the mower further weaken the turf. This (makes) it easier for the fungal pathogen to attack the foliage. “
What causes it?
Ascochyta is a stress-induced infection is favored by low fertility, poor turf management and/or weather conditions that weaken turfgrass plants. Damage can appear any time of year but is most common during late spring and early summer when weather conditions shift from cold and wet, to hot and dry.
This year weather conditions did shift very quickly around Memorial Day weekend, with record warm temperatures and relatively dry conditions following a long cool spring period.
Over watering and poor irrigation uniformity can also make your lawn more susceptible to Ascochyta.
Ascochyta fungi survive on dead leaves or clippings in the thatch layer. During spring wet periods, fungal structures ooze thousands of spores, which are spread to healthy leaves through splashing rain, irrigation, mowing, foot traffic and other lawn management activities.
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The good news is lawns affected by Ascochyta usually recover almost as quickly as they were damaged. This disease may appear severe and affect large areas of turf but seldom is the damage permanent. Since the plant crowns are not killed, they regenerate new foliage within about two weeks. During this time dead leaf tips are mowed off and the damage disappears.
Adjusting your cultural practices is the best way to manage Ascochyta, rather than using of fungicides. Kreuser tested several different classes of fungicides last year and had poor results controlling Ascochyta blight.
Good turf management practices to aid your lawn recovery include the following.
• Irrigate in the early morning hours
• Don’t overwater the turf; provide deep infrequent irrigation
• Manage thatch and promote water infiltration through soil aeration in spring and/or fall
• Don’t allow the turf to go into drought/moisture stress during the growing season
• Avoid excessive applications of nitrogen by using slow-release nitrogen fertilizers
• Mow on a regular schedule and make sure your mower blade is sharp
• Avoid mowing during wet weather
• Maintain your lawn at 2½ to 3 inches in height
For more information on managing your lawn this summer.
• Managing Your Lawn in Summer Heat, https://turf.unl.edu/turfinfo/managing_your_lawn_in_summer_heat.v2.pdf