Ascochyta Leaf Blight

A Fungus that Appears Quickly and Causes Large Bleached Patches

What Is Ascochyta Leaf Blight?

Ascochyta Leaf Blight is a stress-induced fungal disease found in lawns during the late Spring and Early Summer. Many grasses are susceptible, but Kentucky Bluegrass, Tall Fescue and Perennial Ryegrass are the among the most common victims. Ascochyta Leaf Blight causes bleached, dead, or straw-like irregular patches in the grass that come on very quickly, sometimes even overnight. From a distance, the straw-colored areas can resemble drought stress. While this disease looks very serious when outbreaks are widespread, it is actually quite harmless. Ascochyta Leaf Blight does not cause any permanent damage to the lawn.

Confirm your case by inspecting a few infected blades carefully. You will often notice grass blades that appear brown or dried out in the middle, but still remain green at the tips and near the base. Some will be two thirds bleached with a green third of the blade at the roots. You may also see very small, dark brown, flask-shaped fruiting bodies on your grass blades, often easiest to see with a magnifying glass. Roots are rarely affected and so the entire plant will not usually die off.

What Causes Ascochyta Leaf Blight?

First, the weather may just be the culprit! This fungal disease typically plagues lawns when the weather alternates between hot, dry periods and cool, rainy conditions. The disease most often affects turf that is stressed. This disease will spread very fast by foot traffic, rain, and improper lawn mowing practices. Commonly, lawn mowers pick up the fungus and spread the disease throughout the lawn, creating a stripe-like pattern in the lawn. Cultural practices are the only way to help get rid of this disease.

How To Get Rid Of Ascochyta Leaf Blight?

Proper Watering

Watering properly is key to controlling Ascochyta Leaf Blight. Lawns that are poorly watered are often more affected than those that are not. We always recommend deep, infrequent waterings. Shoot for one inch of water, once a week. Do not water so much that you have standing water and soggy soil hours later. Grass that is watered deeply will have deeper, stronger roots. Deep roots mean healthier grass overall. Also important to note, lawns that are very frequently watered and then suddenly not watered are more susceptible to the disease, which is like a quick weather change from cool and wet to hot and dry. So if you do need to change your watering habit, do so over a few weeks.

Proper Mowing

Smart mowing also helps prevent Ascochyta Leaf Blight. Avoid mowing in the morning when the lawn is still wet from dew or overnight watering. Wet grass allows disease to enter through fresh cuts and makes it easier for the fungus to spread. Instead, mow in the afternoon when the surface moisture has dried.

Sharpen your mower blades, dull blades tear the grass instead of cutting it cleanly, leaving it open to infection. Also, avoid cutting the grass too short; never remove more than one-third of the blade at a time. Grass needs time to recover from mowing, and maintaining a height of around 3.5 inches helps reduce stress, discourage weeds, and prevent browning.

Other Tips For Resolving Ascochyta Leaf Blight

A quality fertilizer program will help your lawn stay healthy and recover more quickly if it's affected by Ascochyta Leaf Blight. Regular feeding strengthens the root system and Improves the lawn’s natural resilience to stress and disease.

We do not recommend using a fungicide, as it can also kill off beneficial microorganisms in the soil. This can lead to long-term imbalances and make your lawn dependent on bi-weekly fungicide treatments for the rest of the season which we want to avoid.

Admittedly, the disease is also likely to resolve itself and go away on its own in a few weeks. Remember, it rarely affects the roots, and therefore, does not kill the entire plant. Once the weather conditions improve and with any proactive measures you choose to take, you will be able to mow off the damaged part of the grass blades in a matter of weeks.

How To Prevent Ascochyta Leaf Blight?

We recommend doing a Lawn Aeration twice annually (Fall and Spring), which adds oxygen to the soil, reduces thatch and encourages deeper root growth. This also alleviates soil compaction, allowing roots to stretch out more and grow stronger. We also recommend you dethatch your lawn each year in the Fall to increase water penetration and reduce hiding spots for fungal spores. 🔗 For more in-depth information, check out this article from Iowa State University Extension: https://yardandgarden.extension.iastate.edu/encyclopedia/ascochyta-leaf-blight