How To Treat Ascochyta Leaf Blight On Lawns

 Ascochyta Leaf Blight

Ascochyta leaf blight can be a cause of concern for homeowners when they see their once lush and green lawn suddenly covered in unsightly dry patches. Although this fungal disease is minor and harmless, it can easily be mistaken for more serious turfgrass diseases. This comprehensive guide will discuss how to identify, control, and prevent Ascochyta leaf blight on your lawn, ensuring that your turf remains healthy and vibrant.

Signs of Ascochyta Leaf Blight

Identifying Ascochyta leaf blight can be challenging as its symptoms often resemble drought stress. However, there are some clear signals that can help you tell the difference. Keep an eye out for the following symptoms:

Sudden straw-colored patches

Ascochyta leaf blight causes large straw-colored patches to appear on the lawn seemingly overnight. These damaged areas have irregular shapes and can appear suddenly, even on a lawn that was perfectly green the previous day.

Stripe-like patterns

If you notice parallel stripes following your mower’s pattern across the turf instead of patches, it may indicate Ascochyta leaf blight. These straw-colored stripes result from fungi on your mower’s wheels.

Green blades interspersed with dry ones

Despite the appearance of complete dryness, closer inspection will reveal green blades of grass interspersed between the straw-colored ones.

Partly green, partly dry leaves

Damaged grass blades exhibit a dry, straw-colored tip that is often collapsed in half vertically, taking up to ⅓ of the blade’s length. Some grass may show a dry segment in the middle of the blade, with the top and bottom still green. In certain cases, a purple discoloration may spread across the green blade.

No crown or root damage

Unlike other diseases, Ascochyta leaf blight does not attack the crown and roots of your grass. If you observe damaged or rotted roots after pulling out some grass, it is likely a sign of a different disease.

Microscopic fungal signs

Ascochyta leaf blight produces tiny yellow to brown flask-shaped fungal fruiting bodies called pycnidia, which are visible under a hand lens or microscope. These pycnidia pepper the leaf tissue, indicating the presence of the fungus.

What Causes Ascochyta Leaf Blight?

Ascochyta leaf blight is caused by various fungi within the Ascochyta family. However, the precise environmental conditions that trigger the disease remain somewhat of a mystery. Outbreaks of Ascochyta leaf blight are often associated with sudden temperature increases following periods of high humidity. Faulty lawn care practices can also contribute to the disease’s activation. These practices include:

  • Faulty sprinkler systems result in uneven irrigation and create overly moist or dry areas in the lawn.
  • Frequent mowing provides more opportunities for the fungus to spread and infect healthy grass.
  • Dull lawn mower blades tear the grass instead of making clean cuts, leading to slower healing and increased susceptibility to infection.
  • Overfertilization with excessive nitrogen promotes rapid grass growth and more frequent mowing, making the blades more vulnerable to Ascochyta infection.
  • Compacted soil hinders proper water absorption and root development, making the grass more susceptible to diseases.
  • Thick thatch provides an ideal environment for the survival and spread of Ascochyta fungi.
  • Overwatering creates favorable conditions for fungal growth and prevents the development of deep root systems in the grass.

When is Your Lawn Exposed to Leaf Blight Disease?

Ascochyta leaf blight outbreaks typically occur during the transition from cool and wet conditions to hot and dry weather, which is usually in late spring and summer. It takes approximately 10 days for the disease to take hold after a sudden increase in temperature. The most severe outbreaks of Ascochyta leaf blight occur from June to August.

The fungus responsible for Ascochyta leaf blight survives winters as spores in thatch and grass clippings, protected in pycnidia structures that are resistant to extreme temperatures and drought. This means that the disease can return the following summer if not effectively eradicated.

How to Test for Ascochyta Leaf Blight

To confirm the presence of Ascochyta leaf blight, you can perform a simple test. Visit a damaged area of your lawn and look for blades of grass that exhibit specific signs of the disease, such as a dry segment in the middle of the blade or blades with the top ⅓ dried, tan-colored, and collapsed in half vertically. Although these visual cues may indicate Ascochyta leaf blight, for a definitive diagnosis, it is best to collect a sample of the damaged grass and send it to a plant pathology lab for testing.

While the test results may not be available by the time symptoms disappear, knowing whether Ascochyta leaf blight is present can help you take preventive measures for the following year.

Lawn Diseases That Can Be Confused With Leaf Blight

Ascochyta leaf blight symptoms can sometimes be mistaken for other common lawn diseases, such as dollar spot and brown patch. It’s important to differentiate between these diseases to apply the appropriate treatment. Here’s how to distinguish Ascochyta leaf blight from these similar conditions:

  • Dollar Spot: Dollar spot, another cool-season grass disease that occurs during summer, starts with small yellow or straw-colored circular spots. These spots can merge into larger, irregularly shaped patches, similar to those caused by leaf blight. However, dollar spot lesions on individual leaves are tan-colored with reddish-brown margins, while leaf blight affects the entire blade uniformly. Additionally, dollar spot produces a whitish mycelium visible on soil and grass.
  • Brown Patch: Brown patch affects turfgrass by causing circular and oblong lesions on the blades. These lesions have a straw-colored center and a brownish edge. Over time, the lesions can grow and cover the entire surface of the grass blades, creating a “frog-eye” or donut appearance. Unlike leaf blight, the brown patch also spreads whitish fungal threads across the soil and grass.

How to Prevent the Ascochyta Leaf Blight

Contrary to some other lawn diseases, Ascochyta leaf blight does not require the use of fungicides for treatment. Instead, it is best controlled through cultural practices and proper lawn care techniques. Here are some essential preventive measures and treatments for Ascochyta leaf blight:

1. Keep Lawn Mower Blades Sharp

Regularly check your lawn mower blades, especially if the mower isn’t cutting as cleanly as it should. Sharp blades make clean cuts that heal faster, reducing the time for fungi to infect the grass.

2. Avoid Mowing Wet Grass

Mowing wet grass can lead to clumping and make it challenging for the mower blades to achieve a clean cut. When you mow in the mornings with heavy dew or just after rain or irrigation, you expose your lawn to more wounds, providing entry points for Ascochyta fungi.

3. Mow Infected Areas Last

Always leave the infected areas for the last part of your mowing session. Afterward, thoroughly clean your mower to prevent the spread of the fungi. Additionally, make sure to collect and dispose of grass clippings properly, ensuring they don’t spread to healthy parts of the lawn. Ascochyta can easily spread through lawn care tools and equipment.

4. Limit Nitrogen Fertilizer Applications in the Spring

Avoid excessive nitrogen fertilizer applications in the spring, as this can lead to accelerated grass growth and more frequent mowing. Overgrown grass is more susceptible to Ascochyta infection due to increased opportunities for fungi to penetrate the tender blade tissue. Instead, consider postponing fertilizer application until the turf greens up and reaches its normal growth rate for the season. To promote root development, you can amend the spring soil by topdressing with compost or using a balanced natural fertilizer containing equal nitrogen and potassium.

5. Periodically Check Sprinkler Heads

Regularly check your sprinkler heads to ensure they are functioning correctly. Clogged or poorly positioned sprinkler heads can result in uneven irrigation, creating areas of excessive moisture or drought stress in your lawn. Such conditions can make your grass susceptible to Ascochyta leaf blight. Conduct a sprinkler system audit in early spring before the turf green-up and whenever there are signs of improper water distribution. Adjust the sprinkler nozzles, clean clogged pipes or sprayers, and repair or replace broken sprinkler heads to ensure your grass receives proper irrigation.

6. Avoid Excessive Irrigation

Overwatering your lawn can create an environment favorable for fungal disease development, including Ascochyta leaf blight. Follow the correct lawn irrigation practices for your grass type, watering deeply and less frequently to encourage the development of robust roots instead of fungi. Consider installing a timer and automating your sprinkler system to maintain a consistent watering schedule.

7. Aerate the Lawn Yearly

Core aerate your lawn once or twice a year to alleviate soil compaction and improve water flow. This practice is especially crucial for lawns with heavy clay soils that are prone to compaction. If your turf experiences heavy foot traffic, more frequent aeration may be necessary. Core aeration loosens the soil, allowing for proper drainage and preventing moisture from accumulating near the soil surface.

8. Apply Humate Soil Conditioner on Clay Soil

If you have heavy clay soil that is prone to compaction despite regular aeration, applying a humate soil conditioner can be beneficial. Humate soil conditioners are rich in organic matter, humic acid, and fulvic acid. These products promote the development of beneficial microorganisms, improving soil structure, water absorption, and nutrient availability. Consider using products such as Live Earth Products’ Humate Soil Conditioner or Microlife Humates Plus 0-0-4 to enhance the health of your clay soil.

How to Repair the Lawn After Leaf Blight

The good news is that the damage caused by Ascochyta leaf blight is temporary and merely cosmetic. In most cases, turfgrass recovers without intervention within 2 to 3 weeks. To aid the recovery process, follow these steps:

  1. Mow and rake the affected patches to remove dry, straw-colored tips and expose more of the lower green blades.
  2. If the patches are still noticeable, you can temporarily cover them with grass paint until they fully recover and can be mowed.
  3. During summer, cool-season grasses naturally slow down their growth. Applying slow-release nitrogen fertilizer can support their development, but be cautious not to overstimulate growth, as it can make the grass more vulnerable to heat and drought stress, increasing the risk of other severe fungal diseases.


What’s the Best Fungicide for Leaf Blight?

Fungicides are usually unnecessary for treating Ascochyta leaf blight, as the disease is cosmetic and resolves on its own within a few weeks.

What Causes Lawn Blight?

Lawn blight, specifically Ascochyta leaf blight, occurs when environmental conditions transition from cool and wet to hot and dry. The disease is triggered by sudden increases in temperature following periods of high humidity.

What Does Blight Look Like on Grass?

Blight-on grass resembles drought stress, resulting in irregular patches of straw-like, blighted grass that appears dry and dead from a distance.

When to Call a Lawn Care Professional

If you suspect your lawn is affected by a disease, it is best to consult a lawn care professional for accurate diagnosis and treatment. They can help identify whether it is Ascochyta leaf blight or another more severe condition and provide guidance on proper lawn care practices to facilitate recovery and prevent future infestations. ECO Lawn Utah can connect you with the top lawn treatment experts in your area, ensuring that your lawn receives the best care possible.


In conclusion, by being vigilant and implementing proper lawn care practices, you can effectively identify, control, and prevent Ascochyta leaf blight in your lawn. With the information in this guide, you can maintain a healthy and vibrant turf free from the cosmetic concerns caused by this fungal disease. Remember to follow the recommended preventive measures, such as keeping your lawn mower blades sharp, avoiding mowing wet grass, and periodically checking your sprinkler system. By implementing these practices, you can ensure that your lawn remains resilient and beautiful throughout the year.