Yellow Patches: How To Deal With Lawn Disease?

Nothing ruins a beautiful lawn faster than those stubborn yellow patches popping up out of nowhere. And right before your big backyard BBQ, too! One day, your grass is lush green, and the next, it looks like it’s throwing in the towel. What gives?

Lawn yellowing can be caused by all sorts of things—fungal infections, nutrient shortages, or even Fido’s favourite bathroom spot.

But don’t worry, we’ve got your back! Today, we’ll help you figure out what’s causing those annoying patches and, more importantly, how to get your lawn back to looking its very best.

What Causes Yellow Patches On Lawns?

1. Fungal Infections: When Your Lawn Catches A Cold

Fungal diseases thrive in warm, humid conditions and can quickly turn your green lawn into a patchy mess. Here are some of the most common fungal infections that cause yellowing:

• Dollar Spot: Small, round, yellow, or straw-coloured patches about the size of a dollar coin. Often occurs in humid weather and spreads when grass is cut too short.
• Rust Disease: A powdery, orange-yellow coating on grass blades that rubs off on your shoes. It’s common in undernourished lawns and spreads easily in wet conditions.
• Fusarium Patch (Snow Mould): Circular, yellowish patches that appear in cool, wet conditions, often after snow melts.

Here’s how you can tell if it’s a fungal infection:

• Yellow patches have distinct, circular patterns
• Grass blades may have a powdery or slimy coating
• It spreads over time, worsening in humid or damp conditions

2. Nutrient Deficiencies: When Your Lawn Needs a Balanced Diet

Grass needs a balanced diet to stay healthy. If your lawn isn’t getting enough of the right nutrients, it can develop yellow patches. The most common deficiencies include:

• Nitrogen Deficiency: Grass turns pale yellow-green and grows weakly. This is one of the most common causes of lawn yellowing.
• Iron Deficiency: Results in yellowing between leaf veins, creating a striped look. More common in alkaline or compacted soils.
• Potassium Deficiency: Causes yellow or brown leaf edges and weakens the grass’s resistance to disease and drought.

Here’s how to tell it’s a nutrient deficiency:

• Yellowing is uniform and spread across the lawn rather than in circular patches.
• Growth is slow, and grass appears thin or weak.

3. Overwatering or Underwatering: The Fine Line Between Too Much and Too Little

Watering habits play a big role in lawn health. Too much or too little water can both cause yellowing:

• Overwatering: Drowns the roots, leading to oxygen deprivation and fungal growth. Grass may feel spongy and weak.
• Underwatering: Causes dry, brittle grass that turns yellow or brown. This often happens during summer droughts.

You can identify if watering is the problem if:

• The soil feels soggy, or puddles form after watering; you may be overwatering.
• The grass doesn’t spring back when stepped on; it may be too dry.
• Yellowing appears in random patches and worsens during extreme weather.

4. Pet Urine Burns: When Your Dog is the Culprit

If you have a dog (or rabbit), those yellow patches might be from urine damage. Dog urine contains nitrogen, which in small amounts can act as fertilizer, but too much in one spot causes burns. Here’s how to be sure:

• Patches are small, round, and often surrounded by a ring of extra-green grass.
• More common in areas where your pet frequently relieves themselves.
• New patches continue appearing in the same spots.

Here are tips on how to fix dog spots on your lawn.

5. Soil Compaction: When Grass Suffocates

If your lawn gets a lot of foot traffic, the soil underneath can become compacted, making it difficult for grass roots to absorb water and nutrients. This often leads to patchy, yellowing grass. You can tell if:

• Grass in high-traffic areas looks weaker than the rest of the lawn.
• Water runs off instead of soaking into the soil.
• Trying to push a screwdriver into the soil is difficult due to hardness.

6. Mowing Mistakes: Cutting Too Short or Using Dull Blades

Believe it or not, how you mow your lawn can affect its health. If grass appears uneven, with frayed, yellowing edges, or the yellow patches are more prominent after mowing – your technique or equipment could be the problem. Common mistakes:

• Scalping the Lawn: Cutting grass too short weakens it, making it more susceptible to disease and yellowing.
• Dull Mower Blades: Tearing rather than cutting grass leads to frayed edges that dry out and turn yellow.
• Grass Too Long: Sometimes, grass that is overgrown can limit the amount of sunlight that reaches the soil, which can result in trapped moisture and loss of air exposure to the roots.

7. Pests: When Bugs Are to Blame

Certain insects, like grubs and chinch bugs, feed on grass roots, weakening the lawn and causing it to turn yellow. You can pinpoint a pest problem when:

• Patches of grass pull up easily, revealing white grubs underneath.
• Yellow areas seem to spread despite proper watering and care.

How to Treat Yellow Patches and Restore Your Lawn’s Health

Once you’ve identified the cause of yellow patches on your lawn, it’s time to take action.

• Apply a fungicide if you suspect a fungal infection like dollar spot, rust, or fusarium patch. Choose an appropriate treatment for your specific issue.
• Water in the morning to prevent moisture from sitting on the grass overnight, reducing the chances of fungal growth.
• Aerate compacted soil improves drainage, increases oxygen flow to roots, and promotes healthier grass growth.
• Use a nitrogen-rich fertilizer like our SoilBooster™, which contains over 70 different minerals and nutrients. If your grass looks pale or weak, SoilBooster™ will bring it back to life.
• Supplement with iron if the yellowing appears in streaks or between leaf veins, especially in alkaline or compacted soils.
• Avoid overwatering by ensuring the lawn receives about 1 to 1.5 inches of water per week. Let the soil dry out slightly between watering sessions to prevent root rot.
• Improve drainage in problem areas by adding compost or organic matter to the soil, helping water move through the root zone more effectively.
• Reseed damaged areas with a lawn repair mix if urine spots or other damage have killed the grass.
• Raise your mower height to avoid cutting grass too short, which weakens it and makes it more vulnerable to stress and disease.
• Keep mower blades sharp to ensure a clean cut, preventing jagged edges that can turn yellow and dry out.
• Overseed with disease-resistant grass varieties to create a thicker, healthier lawn that naturally resists pests and infections.
• Apply organic compost or topdressing to enrich the soil, improve moisture retention, and promote microbial activity that supports root health.
• Control lawn pests by checking for signs of grub or chinch bug infestations and applying treatment if necessary.

The Grass Can Be Greener on Your Side!

Restoring a yellowing lawn isn’t about quick fixes; it’s about getting to the “root” of the problem. Whether it’s adjusting your watering habits, feeding your lawn the right nutrients, or tackling a sneaky fungal issue, consistent care is key.

With a little effort (and some expert help), those unsightly yellow patches will be a thing of the past, and your lawn will be back to its lush, green glory.

If you want pro-level lawn care without the guesswork, our GreenKeepers are here to help! From fertilization to aeration and weed control, we have the tools and expertise to keep your lawn thriving year-round.

Check out our lawn care packages and reserve yours soon—we get booked pretty quickly.

If you’re looking for a specific service, get your free estimate here.

We’re in Winnipeg, Regina, Red Deer, Edmonton, Saskatoon, and Calgary.