Treating and preventing fungal diseases in my lawn

12 Minute(s) read

Noticed brown patches, discolouration or unusual growth in your lawn? These could be signs of a fungal disease.

Lawn diseases can develop when fungi have favourable conditions to grow, including excessive moisture, poor drainage and limited airflow. The good news is that many common fungal problems can be managed with the right lawn care.

This guide explains how to identify common lawn diseases, what causes them and how to treat and prevent fungus in your lawn.

What is fungal disease in lawns?

Fungal disease occurs when disease-causing fungi infect your grass and damage the turf. Different pathogens can affect the leaves, roots or other parts of the plant, producing different symptoms and patterns across your lawn.

Fungi are naturally present in soil and lawns. Problems are more likely to develop when conditions favour disease, such as prolonged moisture, poor drainage, excessive thatch or stressed grass.

The type of turf, season and growing conditions can also influence how susceptible a lawn is. That makes a correct diagnosis important before deciding on the best treatment.

Signs of lawn disease: what to look for

Fungal disease can look different depending on the pathogen and turf variety affected. Start by checking both individual grass leaves and the overall pattern across your lawn.

Common symptoms can include:

• Brown, yellow or dead patches of grass
• Circular patches or rings that gradually spread
• Yellow, grey, red or purple discolouration
• Spots or lesions appearing on individual grass leaves
• Thin, weak or dying turf
• Unusual fungal growth on or around the lawn

Some diseases may appear similar at first, so don't rely on colour alone. Consider the shape of the affected area, recent weather, moisture levels and how quickly the problem is spreading.

Identifying these signs early gives you a better chance of correcting the conditions contributing to the disease before extensive damage develops.

Common lawn diseases and how to identify them

Different turf diseases can produce similar symptoms, making identification tricky. The appearance, size and pattern of affected areas can help narrow down the issue.

Seasonal conditions matter too. Some diseases favour warm, wet conditions, while others are more likely during cooler winter weather.

Here are four common fungal diseases and how to identify them in your lawn.

Brown patch and fairy ring

Brown patch is a fungal disease commonly associated with Rhizoctonia species. It can appear as circular or irregular brown patches that spread across affected turf. Warm temperatures, high moisture and prolonged wet conditions can favour disease development.

Poor drainage, excessive watering and heavy thatch can increase moisture around the grass surface. Improving these conditions should form part of managing the problem.

Fairy ring has a different appearance. It typically develops as rings or arcs in the lawn, sometimes with darker green grass around the affected area. Mushrooms may also appear when conditions are favourable.

Fairy ring fungi can affect organic matter within the soil and may contribute to dry areas that become difficult to water evenly.

Dollar spot

Dollar spot usually starts as small, pale or straw-coloured spots that can join together as the disease develops. You may also notice lesions across individual grass leaves.

The disease has traditionally been associated with the fungal name Sclerotinia homoeocarpa, although its scientific classification has since changed. For homeowners, the important part is recognising their distinctive small patches and addressing the conditions encouraging disease.

Dollar spot can become an issue when turf is under stress, particularly when moisture remains on the leaf surface for extended periods. Appropriate watering and balanced lawn nutrition can help reduce favourable conditions.

Red thread

Red thread is one of the easier lawn diseases to recognise because affected grass can develop fine red or pink thread-like growth.

From a distance, the lawn may appear to have irregular red, pink or pale patches. Closer inspection of the leaves can help distinguish red thread from other diseases with a similar overall appearance.

The disease is more likely to become noticeable when conditions favour fungal growth and turf is under stress. Supporting healthy growth through appropriate lawn care can help the grass recover.

Winter Fusarium

Winter Fusarium is a fungal disease associated with cool, damp conditions. Unlike diseases that become more active in warmer months, this problem is more likely to appear in cooler weather.

Affected turf can develop yellow or brown patches that may enlarge. Under suitable conditions, fungal growth can sometimes become visible around affected grass.

Reducing prolonged surface moisture and maintaining good airflow can help make conditions less favourable. Avoid overwatering during winter when the lawn is already receiving plenty of natural moisture.

Here’s a quick overview:

These aren't the only turf diseases that can affect lawns. Anthracnose, leaf spot, Leptosphaerulina, Pythium and spring dead spot are other problems you may encounter depending on the turf variety and conditions.

Because different diseases can produce similar symptoms, avoid applying a fungicide simply because your lawn has changed colour. If the problem is severe, keeps spreading, or fails to improve, seek advice to confirm the cause and determine the appropriate treatment.

Common causes of fungal disease

Fungal disease usually develops when the pathogen, susceptible turf and favourable environmental conditions come together. While you can't control the weather, good lawn care can make conditions less favourable for disease.

Excess moisture, poor drainage, incorrect mowing, unbalanced fertilising, compacted soil and excessive thatch can all increase lawn stress. Identifying these contributing factors gives you a better chance of controlling the problem and preventing it from returning.

Excessive moisture and poor drainage

Fungi often thrive when moisture remains around the grass for extended periods. Overwatering, prolonged rainfall and poor drainage can leave the lawn surface wet and create favourable conditions for disease.

Watering late in the day can also leave the grass wet overnight. Where possible, water deeply in the morning so moisture reaches the root zone and the leaf surface has time to dry.

If water regularly pools after rain or irrigation, look beyond your watering schedule. Compacted soil, poor grading or an unhealthy soil profile can restrict drainage and reduce the lawn's ability to absorb water effectively.

Heavy shade can exacerbate the problem because affected areas may stay damp longer. These sections of lawn may require different watering and maintenance compared with turf growing in full sun.

Improper mowing and fertilising

How you mow and fertilise can influence how well your lawn handles disease pressure. Cutting grass too short can place the plant under stress and reduce the amount of healthy leaves available for growth.

Blunt mower blades can also tear rather than cleanly cut the leaf. Keep blades sharp and avoid removing too much grass in a single mow.

Nutrition matters too. A lawn needs appropriate nutrients to maintain healthy growth, but more fertiliser isn't always better. Avoid trying to fertilise your way out of a fungal problem without first identifying what the lawn needs.

Balanced lawn care helps maintain stronger turf that is better equipped to recover from stress and disease.

Compacted soil, excessive thatch and poor airflow

Healthy turf needs water, nutrients and oxygen to move through the soil profile. Compaction can restrict this movement and contribute to poor drainage, weak root growth and ongoing lawn stress.

Aeration can help relieve compacted soil by creating openings for air, water and nutrients to move into the root zone.

Thatch is the layer of organic material that develops between the green grass and soil surface. A small amount is normal, but excessive thatch can hold moisture and reduce airflow around the turf.

Poor airflow can also keep the lawn damp, particularly in heavily shaded or enclosed areas. Where practical, improving airflow and addressing excessive thatch can help create less favourable conditions for fungal disease.

How do you treat lawn fungus?

The best remedy for lawn fungus depends on the disease and its cause. Start by improving conditions that encourage fungal growth, then consider whether a fungicide is needed.

Removing dead material, improving aeration and adjusting your lawn care may be enough for a mild issue. More persistent disease may require an appropriate fungicide product.

Don't expect lawn fungus to go away immediately. Even after the disease is controlled, damaged turf needs time and healthy growing conditions to recover.

Remove dead grass and debris

Start by removing dead grass, excessive thatch and other debris from the affected area. This can improve airflow around the turf and make it easier to assess how much healthy grass remains.

Don't aggressively remove healthy turf in an attempt to kill the fungus. The aim is to clear excessive dead material while giving surviving grass the best opportunity to recover.

Dispose of diseased clippings and keep mowing equipment clean when working around affected areas. Once the disease is under control, appropriate watering and nutrition can support new growth.

Aerate and dethatch your lawn

If the soil is compacted, aeration can help improve the movement of air and water through the root zone. This can support healthier turf while addressing conditions that contribute to fungal disease.

A heavy thatch layer may also need attention. Dethatching removes excessive organic material sitting between the grass and soil surface, helping improve airflow and water movement.

Neither aeration nor dethatching is an instant cure for fungal disease. Instead, they improve the growing environment so your lawn has a better opportunity to recover and resist future problems.

Using a fungicide

If lawn care changes aren't enough, a fungicide may be an appropriate treatment option for some fungal diseases. Correct identification matters because products differ in the diseases they control, their active ingredients, and their application requirements.

Fungicides may work in different ways. Contact fungicides remain on treated plant surfaces, while systemic products are absorbed and move within plant tissue to varying degrees. Some products combine modes of action or provide both systemic and contact disease control.

Always choose a product registered for the disease and turf situation you are treating in Australia. Read the label before use and follow its directions for application rates, timing, protective equipment and whether the product should be applied as a liquid or spray.

Don't apply extra products in hopes of killing the disease faster. More isn't better, and incorrect application can fail to provide effective control.

If you can't confidently identify the disease or determine the appropriate treatment, we recommend seeking professional lawn care advice before applying a fungicide.

How to prevent fungus in your lawn

Preventing fungal disease starts with maintaining healthy turf and avoiding the conditions that allow disease to thrive. Correct watering, mowing, fertilising, aeration and thatch removal can all help reduce lawn stress.

Regular lawn care also makes unusual changes easier to spot. Whether you're dealing with fungal disease, a weed or another lawn issue, early identification can help you take the right action before the problem spreads.

Water correctly and improve drainage

Water your lawn when it needs it rather than following the same schedule year-round. Seasonal rainfall, temperature, soil type, shade and turf variety can all affect how quickly the lawn dries.

When watering is required, morning is generally preferable because the grass has time to dry during the day. Avoid repeatedly leaving the leaf surface wet overnight, as prolonged moisture can favour fungal disease.

Also, watch how water moves through your lawn. Pooling or persistently soggy areas may indicate drainage or soil compaction problems that need attention.

Maintain healthy mowing and fertilising practices

Regular mowing helps maintain healthy growth, but avoid cutting your lawn too short. Use an appropriate mowing height for your turf variety, and keep mower blades sharp to ensure clean cuts.

Try not to mow when the lawn is excessively wet. If you're mowing an area affected by disease, clean your equipment afterwards to reduce the risk of spreading contaminated material across the lawn.

Fertilising should also match your turf's needs and the season. Apply fertiliser according to product directions rather than using extra nutrients as a quick cure for discolouration.

Improve airflow and overall soil health

Healthy soil supports healthy turf. If your lawn is compacted, aeration can improve the movement of air, water and nutrients through the soil and into the root zone.

Keep an eye on thatch, too. Some organic material is normal, but excessive buildup can retain moisture near the grass. Thatch removal may be beneficial when this layer becomes too thick.

Airflow above the lawn matters as well. Heavily shaded or enclosed areas can remain damp for longer, so prune surrounding vegetation where appropriate and avoid unnecessary watering in areas that dry slowly.

These practices won't guarantee fungal disease never appears, but they can create healthier growing conditions and make your lawn less vulnerable to recurring problems.

Treat fungal disease in your lawn with confidence

Fungal disease can be frustrating, but early identification and the right lawn care can make a real difference. Start by identifying the symptoms, then address contributing factors such as excess moisture, poor drainage, thatch or compacted soil.

For more guidance on common lawn diseases and how to treat them, explore our lawn care advice or speak with the Lilydale Instant Lawn team. We can help you understand your lawn's needs and keep your turf in great shape throughout the seasons.