Lawn Fungus and Disease: How to Identify and Treat Common Aussie Lawn Diseases

Few things are more frustrating than watching a healthy, green lawn suddenly break out in yellow rings, brown patches or thin, dying areas seemingly overnight. More often than not, the culprit is lawn fungus, a group of lawn diseases that can take hold fast, especially when the weather turns humid or the mowing and watering routine isn't quite right.

In this guide, we'll break down what causes lawn fungus, how to spot the most common lawn fungus and lawn disease in Australia, how to treat lawn fungus with the right fungicide, and the simple habits that stop lawn fungus coming back.

Lawn fungus spores are present in every lawn, all the time. They only become a problem when conditions swing in their favour, and then lawn fungus multiplies quickly. The most common triggers of lawn fungus are:

• Warm, humid weather or long periods of leaf wetness

• Watering late in the day, so the lawn stays wet overnight

• Poor airflow, heavy thatch or compacted soil

• Too much (or unbalanced) nitrogen fertiliser pushing soft, lush growth

• Mowing too low, which stresses the plant and lets lawn fungus in

The good news is that most of these are within your control. Fix the conditions and you fix the lawn fungus at its source, rather than just chasing symptoms.

It's easy to confuse lawn fungus with grub damage, dry patches or fertiliser burn. Lawn fungus tends to show a few tell-tale signs:

• Circular rings, patches or irregular blotches of discoloured grass

• Yellow, tan, grey or brown areas that spread over days, not weeks

• A thin, greasy or matted look to the leaf, sometimes with fine webbing early in the morning

• Spots or lesions on individual leaf blades

TIP: Head out early in the morning while the dew is still down. Lawn fungus is far easier to spot at that time, and it often shows visible mycelium (fine white webbing) before the sun dries the lawn off.

Most home lawn problems come down to a handful of usual suspects. Here's how to tell them apart and what to reach for.

• Brown Patch: Large circular brown patches, often with a darker smoke-ring edge, in warm humid weather. Treat with Chlortan or Tribeca.

• Dollar Spot: Small, silver-dollar-sized straw-coloured spots that can merge into larger areas. Treat with Tribeca or Impala.

• Fusarium: Pale rings or patches in cooler damp conditions; grass may look water-soaked. Treat with Impala or Chlortan.

• Leaf Spot: Dark spots or lesions on leaf blades, thinning the lawn over time. Treat with Chlortan.

Once you've identified the lawn fungus, act quickly, because lawn fungus spreads fastest when it's left untreated. A broad-spectrum contact fungicide like Chlortan is a great first line of defence against lawn fungus and knocks down a wide range of common lawn diseases. For tougher or recurring lawn fungus, a systemic fungicide such as Tribeca or Impala moves inside the plant for longer-lasting protection.

Getting the best result:

• Always read the label and apply at the correct rate for your lawn size

• Water the product in only if the label directs you to, since many need to stay on the leaf

• Rotate between a contact and a systemic fungicide to avoid resistance

• Follow up with a second application as directed, as lawn fungus can rebound

Treating lawn fungus is one thing, but keeping lawn fungus away is where the real wins are. Dial in these habits and you'll rarely see lawn fungus at all:

• Water early: Water deeply in the morning so the lawn dries through the day, not overnight.

• Mow smart: Keep the blades sharp and never remove more than a third of the leaf in one cut.

• Feed in balance: Avoid dumping heavy nitrogen; a balanced granular feed like Dominate keeps growth steady, not soft.

• Improve airflow: Dethatch and aerate compacted lawns so lawn fungus struggles to take hold.

Lawn fungus can look alarming, but it's very manageable once you know what you're dealing with. Identify the disease, treat it promptly with the right fungicide, and tighten up your watering, mowing and feeding and you'll clear the current outbreak while stopping the next one before it starts.

Want a simple plan that keeps your lawn healthy and disease-free all year? Download our Free Lawn Calendar. It tells you what to do and when, with products matched to the season.