How to Identify, Fight & Prevent Lawn Diseases 

Are you doing everything you can to beautify your lawn but not quite seeing optimal results? Perhaps you’re scarifying, fertilising, aerating, and watering, but your lawn still looks lacklustre and patchy. Could there be an undiagnosed lawn disease preventing your turf from looking its best?

What are lawn diseases?

Fungi are the most common pathogens in the grass, although not all fungi are considered diseases. Fungi play a clear and beneficial role in breaking down organic material and are therefore always present in the grass.

The shift from a beneficial organism to a disease occurs under favourable conditions, such as a lack of soil life or a weakened lawn. Weather conditions also play a role, as unpredictable weather patterns make the effective control of fungi challenging.

Lawn disease: an overview

There is a range of lawn diseases in the UK, but the most commonly found are:

• Snow Mould
• Red Thread
• Fairy Rings
• Powdery mildew
• Dollar spot
• Rust disease
• Pythiu

We’re going to explore these lawn diseases, explaining how to identify them so you can equip yourself with the best possible defense.

Snow mould “Microdochium nivale” / Fusarium & Snow Mould lawn disease

Symptoms: White fluffy patches throughout the lawn, resembling a thin layer of snow (hence the name!). You’ll first notice patches of just a few centimetres in diameter, but eventually, they spread to around 30cm in size. The lawn above ground appears to die off. 

Causes: Too much nitrogen often causes snow mould, which is usually a sign of over-fertilisation from the previous autumn. Alternatively, snow mould occurs in poorly drained soil due to waterlogged turf. 

Occurrence: In cool, damp weather – especially in the winter. 

Lawn Disease Treatment: Prevention is the best treatment here, so loosen the soil surface by scarifying and aerating. 

Red thread / pink patch lawn disease

Symptoms: Reddish/pinkish spots of various shapes, resulting in root death. If you look closely, you can spot the fungi within the blades of grass. 

Causes: A lack of nitrogen, muggy/humid weather. 

Occurrence: Appears frequently in ornamental lawns but can also occur in heavy-use sports lawns. Usually triggered in temperatures from 5-30ºC. 

Lawn Disease Treatment: Apply a nitrogen-rich fertiliser and ensure the soil doesn’t dry out. Turn your sprinkler on in the morning so that the grass blades can dry out during the afternoon. You’ll be able to rake out the dead fungal remnants within a few days. 

Fairy rings lawn disease

Symptoms: Brown or dark green circles from 4.5m-9m in diameter. The fungus creates a waterproof (or hydrophobic) layer on the soil surface, resulting in starved roots, producing brown, dead grass rings. Alternatively, the nitrogen released when the fungi consume and decompose organic matter causes dark green circles. 

There are three classifications of fairy ring lawn disease:

• Type 1: Dead, brown, wilted grass rings
• Type 2: Dark green rings
• Type 3: Mushroom/toadstool rings

Causes: Drought conditions or mowing too short usually induces Types 1 and 2, while humid or soggy conditions often result in Type 3.  

Occurrence: Most notably between spring and autumn.

Lawn Disease Treatment: In all cases, dethatch your lawn and aerate. Remove nearby tree stumps or roots as these provide fungal stimulation. After dethatching, topdress the soil with a fine layer of high-quality lawn sand. For dark green rings, use a high-nitrogen fertiliser to mask the circles. For brown rings, aerate the soil, then drench the lawn with a wetting agent (a chemical to help the water spread and penetrate).   

Powdery/downy mildew

Symptoms: You’ll see powdery mildew at the top of your grass blades and downy mildew on the leaves at the soil surface. Mildew appears as white/grey fluff – if you look closely, you’ll see black dots within the fluff. Eventually, the grass will dehydrate and die. 

Causes: Mildew occurs as a result of high humidity. 

Occurrence: Spring and summer in high humidity. It most frequently appears on shaded parts of your lawn.

Lawn Disease Treatment: You could simply wait until the temperature drops, which deactivates the fungus. If you want to fight it manually, dust the grass with a sulphur-based fungicide. 

Dollar spot disease

Symptoms: Brown-coloured coin-sized spots, presenting as light brown circles, surrounded by a dark brown, almost red border. 

Causes: Dollar spot thrives in alternating humid, then warm weather (with cool nights). Fescue grasses are particularly susceptible.

Occurrence: Late spring and late autumn.

Lawn Disease Treatment: Feed your lawn with a high-nitrogen fertiliser or spread lime. If the fungus is stubborn, use an organic fungicide.

Rust lawn disease

A slow-acting fungus that results in yellow or orange traces on the grass blade. Rust sits on the blade and is easily brushed off, which can help spread the infection. There are three principal types of rust disease: 

Crown rust:

A yellow/brown withering at the tips of the grass blades. Starts as tiny yellow spots and spreads across the tips of the leaf. Results in dusty spore deposits that look a little like pustules.  

Brown stain rust:

Brown dots that spread across the entire leaf.

Orange stripe rust:

Noticeably stark yellow/orange fungus that affects the entire leaf of the grass plant in a stripe. It quickly spreads across the whole lawn. 

Causes: Rust lawn diseases are often caused by poorly nourished soil and over-cutting of the leaves. The spores are easily transmitted by foot traffic from animals and humans and could be spread with standard gardening tools.  

Occurrence: Potentially year-round, but increased risk during a warm, wet summer, followed by a warm autumn. 

Lawn Disease Treatment: The best treatment is prevention, so avoid rust by ensuring your lawn remains in good condition. Provide the correct amount of fertiliser, and use a high-potassium fertiliser in the autumn to strengthen your turf over the winter. Use a high-nitrogen fertiliser in the spring to give the turf a growth burst and mow, but don’t mulch. Remove the clippings after cutting.  

Pythium lawn disease

Symptoms: Also known as Root Rot, pythium appears as sunken, brownish areas on your lawn, with a slimy film along the stalks of the blades. 

Causes: Drought stress, waterlogging, high soil pH.

Occurrence: Mainly in the summer or autumn, when it’s hot and soggy. 

Lawn Disease Treatment: Aerate the soil to loosen it and remove the thatch layer with a rake or scarifier – this improves your soil’s drainage. When watering your lawn, sprinkle in the morning to allow the turf to dry during the afternoon. Avoid watering in the evening, as night moisture encourages further spread.  

Could the disease actually be a pest infestation?

Many lawn diseases present in a similar way to pest infestations. For example, dollar spot looks similar to a chafer grub infestation.

Alternatively, dollar spot could be a leatherjacket infestation.

Your lawn patches could be a nutrient deficiency

Alternatively, the yellow patches in your turf could result from a nutrient deficiency.

Ultimately, the best way to prevent fungal lawn diseases is to maintain your soil, providing enough nutrients to support your lawn’s optimal growth. There’s an NPK fertiliser for every season, so make sure you use the correct fertiliser to help your lawn flourish throughout the year. 

Carrying out a soil test helps ascertain the acidity of your soil – too acid, and your grass plants will suffer (and weeds will thrive). Adding garden lime to your soil helps neutralise acidity.

Preventing lawn diseases

The occurrence of lawn diseases is not solely dependent on the time of year. Here’s what you can do to prevent lawn diseases:

Sufficient light
Direct access to sunlight helps minimise excessive moisture from the soil surface, helping prevent fungal growth.

Good airflow
Mow your lawn regularly to help improve the airflow over the soil surface, preventing soggy soil.

Minimal thatch
Thatch is the organic matter that collects over the soil surface. The more thatch around your grass plants, the more likely fungal infections will occur.

Minimal compaction
Hard soil around grass roots inhibits leaf growth, providing more space for fungal infections to develop. To achieve this, it’s crucial to fertilise, water, and aerate your lawn. Aeration involves creating holes in the ground to strengthen the roots of your lawn.

Regular mowing
Following the 1/3 rule to avoid cutting the grass too short, enhances grass resilience against diseases. Mulching after mowing returns nutrients to your lawn. Ensure the grass doesn’t suffocate by removing (fall) leaves and coarse organic matter, and perform scarifying if necessary.

FAQ‘s

Ready to treat your lawn disease? Or do you have more questions?

We hope you’ve got all the information you need to make an informed decision about how to identify, fight, and prevent lawn diseases that could be affected your lawn. But if you have any further questions, please don’t hesitate to get in touch. 

We love to hear from you, so send us an email, and we’ll get back to you as soon as possible. 

Happy gardening!

Louis Hooft

Founder & Lawn expert

Introducing Louis Hooft, the founder of MOOWY and your reliable expert. With a profound love for stunning lawns and extensive experience in garden maintenance, Louis is here to assist garden enthusiasts in achieving a greener and livelier outdoors than ever before. Count on Louis for invaluable tips, clever tricks, and top-notch products to make your garden flourish!