Ascochyta Leaf Blight: What Are Those Yellow Tire Tracks on My Lawn?

When hot, dry summer weather hits, your lawn is already under stress — and sometimes it shows. If you’ve noticed sudden straw-colored streaks or patches on your grass, especially after a stretch of heat and drought, you might be seeing Ascochyta leaf blight. It’s most often seen in Kentucky bluegrass, but tall fescue and perennial ryegrass can also be affected. The good news? It looks worse than it is.

What is Ascochyta Leaf Blight?

Ascochyta leaf blight is a foliar disease (meaning it only affects the blades of grass, not the roots).

You’ll usually see it throughout the summer when high heat, low rainfall, and inconsistent watering combine.

From a distance, it often looks like drought stress or dead turf — with straw-colored patches or stripes. Up close, you may see leaf tips pinched and discolored.

It also spreads easily through mowers, foot traffic, or rainfall, which is why it can appear in streaks or patterns.

Will It Kill My Lawn?

In most cases—ascochyta leaf blight is purely cosmetic, affecting only the leaf blades and not causing permanent damage to your lawn. The good news is that healthy grass typically grows out of it on its own with proper care in a few weeks.

However, in rare situations like the record-breaking drought and prolonged 95°F+ temperatures we experienced in 2024, some grass struggled to fully recover from the blight. During extreme heat stress, the damage can be more severe and recovery slower.

So while usually not a threat to your lawn’s survival, if harsh conditions persist, it’s important to stay vigilant and focus on good watering and maintenance to support your turf’s health.

How to Help Your Lawn Recover

Here are a few steps you can take to help your lawn bounce back:

✅ Water properly
Ascochyta is most often seen during hot, dry weather, when turf is already stressed. Proper watering not only helps your lawn recover but can also help prevent the disease from appearing. Aim for 1–1.5 inches per week, ideally between midnight and 6 a.m.

💡 Pro tip: if you can’t easily push a screwdriver at least 6 inches into the soil, your lawn probably isn’t getting enough water. (And watch out for those sprinkler lines!)

✅ Mow smart
During summer, mow higher — around 4 to 4½ inches — to help grass stay cooler and retain moisture. This is a general guideline and can vary slightly depending on your conditions. Avoid mowing when the grass is wet, and never remove more than ⅓ of the blade at a time.

✅ Aerate in fall
Core aeration in the fall relieves compaction, improves root health, and breaks up thatch — where disease can linger. Stronger roots and better air flow help your turf handle stress more easily. Pairing core aeration with seeding can also help introduce new varieties of seed that are better resistant against common threats like drought and disease.

✅ Fertilize appropriately
Healthy, vigorous grass recovers faster and is better able to outgrow leaf damage. Don’t overdo it, but regular, balanced slow release fertilization helps keep your lawn resilient.

Be Patient — It Will Grow Out

There’s no fungicide treatment for Ascochyta leaf blight — it just needs time and good care to grow out. If conditions stay hot and dry, it may linger for a few weeks, but it will rarely kill permanently damage your lawn.

Learn More

At Green Valley, we don’t treat lawn diseases, but we’re happy to help you understand what’s happening with your lawn and advise you on the best care practices.

Have questions about watering, mowing, or aeration? Contact us today or check out our other blog posts.