Many diseases can affect lawns, but one of the most common in the UK is red thread. This fungal infection can leave unsightly patches of discoloured grass, and when it strikes, you will want to take care of it as quickly as possible.
To help, here’s our guide to red thread lawn to explain what the disease is, how to identify it and what to do when it appears, allowing you to nurse your lawn back to health and prevent red thread from returning in the future.
If you want a preview of some of the stuff we’re going to be talking about – as well as some extra tips and hints about dealing with it – you can check out this video before reading on.
What is red thread?
Let’s start at the beginning – what is red thread?
Red thread is among the most common lawn problems you can encounter in the UK and is caused by the fungus Laetisaria fuciformis.
Once it sets in, it can leave patches of discoloured or dead grass, making it an unwelcome if common occurrence.
The good news is that this fungal growth is more of a nuisance than a serious problem because it only attacks the leaves while leaving the roots intact.
This means that although it might look unattractive, it usually won’t damage your lawn permanently, and once the infection clears up, your grass will rebound and grow back naturally without too much extra help.
Why do lawns develop red thread?
Like many other lawn problems, red thread takes advantage of lawns that are in less than perfect health. Lawns growing in soils with low nutrient content are especially susceptible, especially soils that are lacking in nitrogen.
Grasses that are weakened in any way are more prone to developing the fungus, but the fungus also prefers temperatures in the range of 15-25°C as well as moist conditions. This means lawns providing this kind of environment are more likely to be attacked.
Some species of grass are known to be more vulnerable. These include red fescue, bentgrass, perennial ryegrass and annual meadowgrass – along with some more modern grass strains that have low natural resistance.
The spores of the fungus can be carried by air or in water, and they can also be transferred on contaminated garden tools.
Once present, it can lie dormant in the soil for up to two years waiting for the perfect conditions to become active again and spread throughout your lawn.
As long as the conditions are suitable for red thread, the disease can strike at any time of the year.
How to identify it
You will probably first notice red thread as patches of discoloured grass in your lawn ranging from around 7.5cm to 25 cm or even larger. You may also be able to detect a slightly pink tinge to these spots once they develop.
There are two phases to red thread growth. Both are visible to the naked eye, although you are more likely to be able to make a positive identification of the fungus by using a magnifying glass.
In the first stage, you will be able to see thin, red, needle-like strands growing from the blades of grass.
After the first stage, the second stage is characterised by the growth of mycelium, which exhibits a fluffier growth reminiscent of cotton, also with a pink tinge.
If you suspect your lawn is infected by red thread, make sure you inspect it carefully. This is because red thread is similar to several other infections, and if the symptoms don’t match exactly, it’s possible you may be dealing with something else.
How to treat a red thread infection
If you discover red thread in your lawn, the good news is that it’s easy to treat and that your lawn will probably make a full recovery in a short amount of time.
Since red thread usually strikes in lawns that lack nitrogen, the most effective treatment is to feed your lawn with a dose of nitrogen-based fertiliser. This simple action will usually be enough to help the lawn heal itself, allowing you to think more about long-term prevention.
Here’s a short video that shows you how to identify red thread disease and explains how to treat it using nitrogen-based fertiliser.
If your lawn is suffering from a particularly serious attack of red thread, you may also choose to treat it with a fungicide containing trifloxystrobin.
However, while this may help you get on top of a serious outbreak of red thread, it should be used sparingly (no more than twice a year).
Among other reasons, this is because the fungus can develop a resistance to fungicide, and when this happens, the effectiveness of using it will be much reduced.
How do you prevent it in the first place?
The best way to combat red thread is to prevent it from appearing in the first place – and if it does strike, once you have rid your lawn of the fungus, you should take steps to prevent it from returning.
The key to doing this is to understand the conditions in which red thread thrives and then to work towards removing them from your lawn.
Here are some of the steps you should take.
1. Maintain healthy nitrogen levels in your soil
As we’ve already mentioned, red thread tends to develop in undernourished lawns, so ensuring your grass is always well-fed and that the soil contains the right amount of nitrogen is the first step.
Note that if the nitrogen content is too high, it can also lead to an attack of red thread, so make sure the levels in your soil are just right for healthy grass.
2. Ensure your lawn is properly aerated
Since red thread requires a moist environment to grow, maintaining a properly drained lawn is essential. For this, make sure your lawn is properly aerated to allow any water to dissipate rather than sitting on or near the surface.
You can aerate a lawn simply with a fork or by using a dedicated aerator.
Keeping your lawn properly aerated will also reduce compaction, helping your grass thrive and making it more capable of defending itself against red thread and other similar threats.
3. Remove thatch
Having a thin layer of thatch (around 1cm) can be beneficial to your lawn, but if it gets too thick, it can cause problems – including giving red thread a chance to move in.
To prevent this, make sure you scarify your lawn regularly to prevent an excessive build-up of thatch.
4. Remove shade
If your lawn is constantly in shadow, it could be a good idea to remove some of the shade, for example by cutting back overhanging branches.
This will increase ventilation as well as helping with natural evaporation from the sun, and in turn, this will remove the excess moisture that helps red thread develop and thrive.
5. Always make sure your mower blades are sharp
When cutting your lawn, always ensure your mower blades are sharp. If they are blunt, they will tear the grass blades rather than cutting them. Tearing the blades will weaken the grass, making it more susceptible to all kinds of disease – including red thread.
6. Dispose of grass clippings
If your lawn has been infected with red thread, it is important to deal with grass clippings in the proper way.
Since red thread spores can lie dormant for up to two years, you should bag up clippings and destroy them or otherwise dispose of them safely.
If your lawn has suffered an attack of red thread, you shouldn’t put the clippings on the compost heap – otherwise, there is a risk of them surviving, and you may end up spreading them over your lawn and reinfecting it later.
7. Always follow lawn care best practices
Red thread, like almost all lawn infections, preys on lawns that are not in good health. This means following year-round lawn care best practices is the best holistic method of protecting your lawn from a range of possible issues.
To this end, you should know when to fertilise your lawn, when to aerate, when to scarify and when to mow.
We’ve already mentioned using sharp mower blades, and you should also stick to the ‘one-third’ rule that tells you never to remove more than one-third of the height of your grass each time you cut it.
If you remove more than a third of your lawn’s height, you will be placing it under too much stress and, again, you will be inviting red thread and other similar diseases to establish themselves in your grass.
8. Consider iron treatments
You may also consider giving your lawn treatments of iron, perhaps in the form of lawn sand.
Iron is usually used to treat moss, but it can also help harden a lawn against all kinds of disease – including red thread.
An annoying issue – but easy to deal with
As you can see, red thread can be annoying and unwelcome when it appears in your lawn, but it is far from being the most serious or difficult problem to deal with.
When you notice it, red thread is easy to treat – and by following the suggestions in our guide, you will be able to get rid of red thread quickly and efficiently and make sure it doesn’t make a comeback any time soon.