Your lawn is more than just grass—it’s the backbone of your home’s curb appeal, the soft playground for your kids, and the foundation of your outdoor living space. It’s a point of pride for many New Zealanders, and seeing it turn patchy, brown, or speckled with strange colours can be genuinely frustrating.

The culprit is often not a pest, but a disease.

Lawn diseases are typically caused by fungi, and they can spread rapidly under the right (or rather, wrong) conditions. They thrive on stressed grass and are particularly active during periods of high humidity, excessive moisture, or sudden temperature changes. They are the silent assassins of the turf world.

As your local lawn care experts at Jim’s Mowing NZ, we know exactly what fungal foes Kiwi lawns face. This comprehensive guide will walk you through how to spot the signs, treat the infection, and, most importantly,prevent lawn diseases to keep your turf robust, healthy, and beautifully green all year round.

1. Understanding the Enemy—The Big Three Lawn Diseases in NZ

Diagnosing the problem is the first and most critical step. Fungal diseases often look similar, but their preferred conditions and appearance can help you tell them apart.

1. Red Thread (or Pink Patch)

This is perhaps the most common fungal disease in New Zealand and is often a sign of a struggling, nitrogen-deficient lawn.

When It Strikes – Most prevalent in cool, wet weather, typically in late autumn, spring, or during wet summers.
The Signs – You will see irregular patches of light-tan or straw-coloured grass, usually 7 to 25cm in diameter. Look closely at the tips of the grass blades, especially when they are wet. You might spot fine, reddish-pink thread-like growths (called stromata) extending from the tips of the leaves.
The Damage – Red Thread rarely kills the grass roots entirely, but it certainly ruins the uniform look of your lawn.

2. Dollar Spot

As the name suggests, this disease leaves distinct, small spots, which often cluster together to form larger, more widespread damage.

When It Strikes – Favourable conditions are warm days, cool nights, and high humidity, which means it’s most active in late spring, summer, and autumn. It especially targets stressed lawns suffering from low fertility or drought.
The Signs – Look for small, circular, sunken patches of discoloured grass, initially about the size of a 50-cent coin (or a silver dollar). The grass blades in the spot will appear bleached and may have a reddish-brown margin. In the early morning dew, you might see fine, white, cobweb-like threads (mycelium) covering the patches.
The Damage – If left untreated, the spots will merge, creating large, irregular patches of dead grass.

3. Fusarium Patch (or Snow Mould)

This disease can be one of the most destructive, particularly in areas of the lawn that remain damp and sheltered.

When It Strikes – It is a cool-weather disease, thriving in the cool, moist, and overcast conditions of late autumn, winter, and early spring. It’s often worse when the grass is lush due to a high nitrogen application in winter.
The Signs – Initial symptoms are small, yellowish, water-soaked patches that quickly turn a pulpy, reddish-brown. The patches can spread rapidly, sometimes reaching 30cm or more, and may look slimy or greasy. In dewy conditions, you might see a white or pinkish fungal growth around the margin of the patch.
The Damage – Fusarium patch can kill the grass blades down to the crown, resulting in significant bare patches that require reseeding.

2. The Golden Rule of Treatment—Cultural Practices First

Chemical fungicides can be effective, but they are expensive, targeted, and should always be a last resort. The best way to beat a fungal disease is to eliminate the environmental factors that allowed it to take hold. This is often called a “cultural control.”

1. Master Your Watering Schedule

Fungus needs moisture on the grass blade to germinate and spread.

The Change

Never water your lawn in the late afternoon or evening. This allows the grass blades to stay wet all night, creating an ideal breeding ground for fungus.

The Fix

Water only in the early morning (before 10 am). This allows the water to soak in while the grass blades have the entire day to dry out completely in the sun.

The Method

Water deeply and infrequently. Instead of light watering every day, give the lawn a deep soak once or twice a week.

2. Sharpen Your Mowing Routine

A stressed lawn is a susceptible lawn. Poor mowing habits are a leading cause of stress.

The Change

When disease is active, raise your mower height. Cutting the grass too short stresses the plant and leaves less leaf surface for photosynthesis.

The Fix

Mow frequently but never remove more than a third of the grass blade length at a time.

The Clean-Up

If you have active fungus, collect your clippings instead of mulching. This removes the fungal spores and prevents them from spreading across the rest of your lawn, especially when you mow a healthy section next. Make sure to wash your mower blades with a mild bleach solution after cutting an infected area.

3. Improve Airflow and Drainage

Fungi thrive in still, damp conditions. You need to get air moving and water draining.

The Change – Prune back any low-hanging branches from trees or shrubs that are creating excessive shade and reducing air circulation over the lawn.
The Fix – Aerate your lawn. Use a garden fork, or hire an aerator, to punch holes into the soil, especially in compacted or affected areas. This improves drainage and gets oxygen to the roots.
Thatch Management – Remove excessive thatch (the layer of dead grass and organic material sitting on the soil). Dethatching or scarifying with a sturdy rake or machine will remove this moisture-holding layer and greatly reduce the conditions favoured by diseases like Dollar Spot and Fusarium Patch.

4. Adjust Fertilisation

Feeding your lawn correctly is your number one defence.

Red Thread – This is almost always a sign of nitrogen deficiency. A quick application of a nitrogen-rich fertiliser will often cause the grass to rapidly grow out of the infection.
Fusarium Patch – Conversely, avoid high-nitrogen feeds in late autumn or winter, as this encourages the lush, soft growth that this fungus loves. Switch to a lower-nitrogen, autumn/winter specific fertiliser.

3. When to Use Chemical Control (Fungicides)

If cultural controls aren’t working and the disease is severe or spreading aggressively, you may need to apply a fungicide.

Application – Look for a broad-spectrum lawn fungicide approved for use in New Zealand. Common products target a range of fungal issues like Red Thread, Dollar Spot, and Brown Patch.
Coverage – Follow the instructions precisely. You must apply to the entire affected area and usually to a wide border of the healthy lawn surrounding it to prevent further spread.
Timing – Fungicides are generally most effective when applied at the very first sign of an outbreak or as a preventative measure if your lawn is historically prone to a specific disease.

If you are unsure about using chemicals, or need a large area treated, the Jim’s Mowing team is equipped with the knowledge and certified commercial products to apply a professional, targeted treatment that is safe and effective.

Conclusion

A successful defence against lawn diseases in New Zealand starts with vigilance and good lawn care habits. By understanding the common fungal foes like Red Thread, Dollar Spot, and Fusarium Patch, you empower yourself to react quickly.

Remember, a healthy lawn is a resilient lawn. Your best defence is an offensive strategy built around excellent cultural practices: correct morning watering, disciplined mowing, aeration, dethatching, and a balanced feeding schedule. These simple steps create an environment where fungal spores cannot thrive, letting your turf grow thick, green, and vibrant.

If you are struggling with a persistent lawn disease or simply need expert advice and a professional treatment plan to restore your beautiful lawn, the local specialists at Jim’s Mowing NZ are here to help. We’re ready to put the health and beauty back into your piece of the Kiwi landscape!

Happy mowing!

Frequently Asked Questions (FAQ)

Diagnosing Lawn Diseases

Q1: My lawn has brown patches. How do I know if it’s a fungus or just a dry spot?

A: A fungal disease often has a distinct pattern and appearance. Look closely at the grass blades:

Fungus: You might see a ring of active discolouration (yellow/orange/pink), or small lesions/spots on the individual blades. Active diseases like Red Thread or Dollar Spot are usually visible early in the morning when dew is present.
Drought/Dry Spot: The grass will be uniformly brown and brittle, and there won’t be distinct rings or lesions. The soil underneath will be dry and hard.

Q2: What is the most common lawn disease in New Zealand?

A: The most commonly observed fungal diseases in New Zealand are Red Thread and Dollar Spot. They thrive in moist, cool, or humid conditions, especially when the grass is under-nourished or stressed.

Q3: When is the best time of year to look for active lawn diseases?

A: Fungal diseases are most active during periods of high humidity and mild temperatures.

Spring/Autumn: Ideal for diseases like Red Thread and Dollar Spot, as days are mild and nights can be cool and damp.
Summer: High heat combined with wet periods (e.g., thunderstorms or heavy irrigation) can trigger diseases like Brown Patch.

Treatment and Cultural Control

Q4: Should I use a catcher and remove clippings if I have a disease?

A: Yes, absolutely. If you have an active fungal disease, always use your catcher. Leaving clippings on the lawn acts like a blanket, trapping moisture and heat (perfect for fungus), and allows the fungal spores to be spread by the mower blades across healthy sections of the lawn.

Q5: How should I change my watering routine to prevent fungal diseases?

A: The key is to eliminate extended periods of leaf wetness:

Water Only in the Morning: Water deeply and thoroughly between 6:00 AM and 10:00 AM. This allows the sun and air circulation to completely dry the grass blades before evening.
Never Water at Night: Watering in the evening leaves the foliage wet all night, creating an ideal 8-12 hour window for fungal spores to germinate.

Q6: Does a diseased lawn need fertilising?

A: It depends on the disease.

Red Thread is often triggered by low nitrogen. A quick-acting, balanced fertiliser can help the grass outgrow the disease.
For aggressive diseases like Brown Patch, over-fertilising (especially with high nitrogen) can make the problem worse. Focus on balanced nutrients and soil health.

Long-Term Prevention

Q7: My lawn gets very spongy. Is this related to disease?

A: A spongy lawn usually indicates an excessive build-up of thatch (a layer of dead and living organic matter between the grass and soil). Thatch holds a lot of moisture, which is an incubator for fungal diseases. You should dethatch (scarify) or verti-mow the lawn, typically in late spring or early autumn.

Q8: What is aeration and how does it help prevent disease?

A: Aeration (poking holes in the soil) is a vital practice. It:

Relieves soil compaction, allowing roots to grow deeper and stronger.
Improves water and air penetration, reducing surface water pooling.
Encourages microbes that compete with disease-causing fungi. Aerating once or twice a year is a powerful preventative measure.

Q9: When should I consider using a fungicide?

A: Fungicides should be a last resort. Consider using one only if:

You have identified the disease and confirmed it is severe.
You have already adjusted all cultural practices (mowing, watering, fertilising) for at least two weeks with no improvement.
The disease is threatening the entire lawn or a high-value area. Always follow the manufacturer’s instructions precisely.