The Conspicuous but usually cosmetic – Ascochyta blight
This sporadic disease is commonly known to infect Kentucky bluegrass, tall fescue, and perennial ryegrass. The outbreaks generally appear when there is an influx of rain or irrigation around mid to late spring when drainage patterns change. If the lawn has been irrigated recently Ascochyta can be a sign of too much or over-irrigation. When these events happen, this provides a prime environment for this disease. In order to reduce the spread of the disease, wait to mow your lawn until the turf is dry, and try not to mow directly after excessive rain or storm. Additionally, making sure the mower blades are sharp and set to the appropriate height (3 to 3.5″ or taller), can help slow the spread of the disease. Ascochyta blight is a foliar disease and generally, your grass will recover in just a few weeks to a month without any fungicide treatments.
Ascochyta can be found in senescing or dead leaves of many turf/grass species, most commonly found in Kentucky Bluegrass. The disease survives as conidia in pycnidia on dead leaves and can also be found in the clippings that remain in the thatch. These pycnidia are resistant to breakdowns brought on by droughts or high temperatures. From a single pycnidium, thousands of conidia ooze from the wet weather and are then dispersed by rain, irrigation, or mowing. The disease occurs in late spring or summer during periods of warm weather, followed by wet soil conditions from rai, or excessive irrigation.
- Use good cultural practices that reduces grass stress
- Maintain a cut of 3″ or higher
- Sharp Mower Blades
- Avoid mowing in wet conditions
- Maintain balanced fertility – avoid to much nitrogen fertilizer
- Maintain uniform soil moisture
Ascochyta leaf is a blight that affects the leaf and not the root of the plant, so it generally does not kill or cause plant mortality. Your grass usually recovers on its own after a few weeks to a month.
Purdue Landscape Report: https://www.purduelandscapereport.org/article/ascochyta-blight-conspicuous-but-usually-cosmetic/
Author: Lee Miller, 5-22