Common Lawn Diseases
Have you noticed any discolouration or bare patches in your lawn? Or maybe your grass blades have a powdery coating on them? This could be a sign of lawn disease.
Lawn diseases are mostly caused by fungi and can seriously affect the health and look of your grass. That’s why it’s important to be able to recognise different diseases, understand their causes, and know how to treat them.
What Causes Lawn Diseases?
Fungi are usually beneficial for the grass, helping it to break down organic matter. This contributes to the soil’s structure and fertility. However, sometimes they can cause lawn diseases. This often happens when the grass is stressed or weakened, making it more vulnerable. Some common causes include:
- Weather Changes: Sudden weather changes can stress the grass. The wet and cool conditions we often get in the UK also create the perfect environment for fungi to grow.
- Not Mowing Your Grass Correctly: Cutting your grass too short reduces its ability to photosynthesise. Using dull mower blades can also damage the grass by tearing it instead of cutting it cleanly, increasing the risk of lawn diseases
- Too Much Thatch: Thatch is a layer of dead grass and other organic matter that forms on top of your lawn. Too much thatch can block your turf from getting the air, water, and nutrients that it needs. This slows down its growth, providing a breeding ground for diseases.
- Compacted Soil: Compacted soil limits the grass’s root growth. This makes it harder for it to absorb water and nutrients, making it more likely to get a lawn disease. Check out our ‘Lawn Aeration and Scarification’ guide to learn how to prevent this.
- Not Fertilising Your Lawn Properly: Using too little fertiliser will not help your lawn grow strong, while too much can burn the grass and kill helpful bacteria. This often leaves behind a yellow, patchy lawn that is more likely to develop a disease.
Common Lawn Diseases in the UK
Fairy Ring
Fairy ring disease has 3 different types and often appears as full or partial rings of either dead or deeply green grass on the lawn. Toadstools can also appear, especially in late summer or autumn. The rings can reach up to 15 feet in diameter and grow at a rate of 75-150mm per year.
There are over a thousand types of fungi that can cause fairy rings. While the exact scientific reasons why they appear are unknown, they are often found in lawns with excessive thatch, compacted soil, or in the areas that were once woodlands.
While the dark green and mushroom rings are less damaging than the dead grass ones, all three types must be treated. Without treatment, the rings can create a water-repellent layer in the soil, preventing water from reaching the grass roots. Over time, this can cause the lawn to die.
To treat fairy rings, fertilise your lawn regularly to address any nutrient deficiencies and reduce their appearance. Toadstools can be raked or mowed away for the same reason. Scarifying and aerating your grass once or twice will also remove excess thatch and allow the water to reach the turf’s roots. Make sure to also overseed any dead areas with grass seed so that new grass can germinate. This process can take a few years before your lawn is ring-free.
Powdery Mildew
Powdery mildew often affects lawns that have low air circulation and light levels. Because of this, it is commonly found on lawns that grow in the shade or have not been maintained properly. It is often seen between spring and autumn.
Powdery mildew is easy to spot and recognise. According to Homes & Gardens, it looks ‘like someone dusted flour or talcum powder on the grass blades’. Over time, it can spread, causing large yellow patches in the grass, and even kill it.
To treat it, trim any shrubs or trees that may be blocking your lawn’s access to sunlight. Then, scarify your lawn so that it can get more air and sunlight. Additionally, aerating the lawn after scarifying will improve the overall soil health, preventing the disease from spreading. Make sure to avoid fertilisers during this time as nitrogen can contribute to fungus growth, but you can use fungicides to treat the disease. However, it is still important to make sure that the lawn gets enough sun and is properly cared for in the future so that powdery mildew does not come back.
Fusarium
Fusarium patch, also known as snow mould, often appears in mild, damp weather. At first it looks like small, yellow, circular patches that later turn brown. These patches can grow anywhere from around 5cm to 30cm across, often merging together and covering a big part of your lawn. Sometimes, the patches end up having white fluffy strands around the scar that look like candy floss. Over time, it can kill your grass and lead to bare spots.
It is likely to form if your turf has a heavy thatch layer, poor drainage, or if the weather has been cold or warm and damp. Over-fertilising your lawn can also cause this problem, especially if it was done in early spring or late autumn.
To treat it, reduce the amount of thatch and loosen the soil by scarifying and aerating your lawn. Additionally, avoid high-nitrogen fertilisers. Instead, use a fertiliser that is low in nitrogen but high in potassium. You can also use fungicides, but make sure the product you choose has at least one of these active ingredients:
- Benomyl
- Carbendazim
- Fenarimol
- Iprodione
- Chlorothalonil
- Quintozene
Red Thread
Red Thread is often present in lawns that do not have enough nitrogen. It is also likely to be seen during longer periods of warm, wet weather, especially in summer. But it can develop at almost any time of the year. Red thread first appears as pink fungus that forms on the leaves, making them look like red needles. Apart from visual damage, red thread can weaken the turf, increasing its susceptibility to other lawn diseases.
To treat it, make sure that you are regularly fertilise your lawn and aerate it to improve drainage. This will reduce moisture levels. If using fungicides, make sure to choose products that have benomyl, carbendazim, or fenarimol in them.
Leaf Spot
Appearing as small, yellow or brown spots on grass blades, leaf spot disease can thin out the turf by causing the affected leaves to die. The disease thrives in warm and humid weather conditions, usually between March to October. It is also common in lawns that suffer from too much thatch or have been over-fertilised.
Once leaf spot has been observed, it is best to avoid strong fertilisers during spring and summer and prevent thatch by scarifying. Ensure you never remove more than one-third of the grass height in a single mow to allow the grass to regenerate.
Rust
To check if your grass is affected by rust, closely inspect its grass blades. The disease appears as yellow spots on the leaves, often covering them with a brown or black powdery substance towards late autumn.
There are a few reasons why your lawn may suffer from rust. It is likely to form once the temperatures reach above 20°C and if your lawn grows in the shade. Low nitrogen levels caused by not fertilising the lawn enough can also contribute to it.
To manage it, reduce shade by removing or trimming any larger plants that may be blocking sunlight. Correct mowing practices are also important – mow the grass at the correct height and remove the grass clippings after every mow to stop the disease from spreading. Lawn feed that is high in nitrogen will also help the grass by providing it with the nutrients that it needs to fight off the rust.
Anthracnose
This disease can occur at any time of the year but is most common from late summer through to winter. It has two types: basal rot and foliar blight. Basal rot causes grass leaves to turn yellow, with black rot appearing at their base. Foliar blight, on the other hand, appears as irregular yellow or brown patches. It can look very similar to drought, but watering can make it worse.
The disease usually affects lawns that are under stress, such as golf courses. However, it can also affect any lawn that has been poorly maintained. Long spells of wet weather and poorly drained soil also create the perfect conditions for anthracnose to thrive.
To treat it, aerate the soil to relieve compaction and improve drainage. A good lawn care routine is essential to nurse the lawn back to health. This includes regularly fertilising your lawn and following correct mowing practices, such as not cutting the grass too short and ensuring mower blades are sharp. Chemical fungicides can also be used to treat the disease and should contain chlorothalonil, benomyl, or vinclozolin.
Dollar Spot
If you notice small spots on your lawn, no larger than a 10 pence coin, consisting of dead grass that appears brown or bleached, it likely has dollar spot. These spots may merge, forming larger areas of scarring. They can also weaken the turf, creating an uneven surface.
Dollar spot can be caused by poor mowing practices and, just like red thread, is likely to appear during long periods of warm, wet weather. Especially in the summer and autumn.
The best treatment for dollar spot is to water the grass deeply but less frequently and to fertilise it regularly. Check out our ‘Dollar Spot: Turf Disease Treatment’ blog to learn more about how to tackle this disease.
Choosing a fungicide treatment
When treating fungal diseases in your lawn, there are two main types of fungicides to choose from:
• Broad-spectrum fungicides are made to deal with a wide range of fungal diseases rather than focusing on a specific one. These are the best option if you are unsure which fungus is affecting your lawn, as they provide general protection and treatment.
• Narrow-spectrum fungicides are designed to target specific fungal infections. They are highly effective, but only if the disease has been correctly identified. If not, the treatment may not be effective.
Remember, fungicides can cause skin irritation, so make sure that your body is fully covered. This includes always wearing a mask and safety gloves. Children and animals should also be kept away at a safe distance when applying the product.
Pest Infestation or Disease?
Sometimes, pest infestations can be mistaken for diseases. For example, chafer grubs damage grass roots and cause yellow and brown patches on the lawn. These can sometimes be confused with dollar spot.
Leatherjackets can also be mistaken for a disease, as in rare cases, they can cause the lawn to become patchy and result in parts of it dying off.
Since pests often require different treatments to control, make sure to check out our ‘Pests’ guides to ensure you are treating your lawn for the right issue.
Lawn diseases can affect your grass at any time of the year. That’s why spotting them early and knowing how to treat them is key to keeping your garden healthy and looking its best.
A good lawn care routine and proper mowing practices can lower the risk of disease or help your lawn recover more quickly.
