Red Thread - is it worth worrying about?

Updated: Jan 3, 2020

Red thread is the most common turf disease in the UK. It will impact a wide range of surfaces from sports grounds to the common lawn. This post aims to provide an insight as to what is going on, and what can be done.

What is red thread?

Red thread is a fungal disease which attacks the grass plant when conditions suit. It will show up as pink / red patches in your lawn while the disease is active, which suppresses to a straw colour when the attack passes. The disease does not impact the root of the plant, thereby soon recovers. Dis-figuration to the turf is temporary, but these areas may be unsightly for a time.

Red thread in a lawn
A lawn suffering from red thread

When does it form?

Red thread requires warm and wet conditions to form. When conditions are still and humid, this disease can enter the tips of the grass plant when they are sat wet. Being very conditions dependent, red thread favours damp summer conditions, but it can occur all year around such as in a mild November.

What can be done?

It's important to understand that if conditions are extreme, a limited amount of red thread is going to be present in any lawn - a little bit like a little moss over winter if wet enough. There is a number of things which in our experience will reduce the occurrence of red thread.

1) Consider your grass types / species

Our recently renovated lawns gain very little in terms of disease. This is due to a combination of a recently aerated soil, an almost thatch free surface, and the use of modern grass cultivars. We tend to sow with finer ryegrasses which provide excellent aesthetics, but also an impressive disease tolerance. Older lawns with a high proportion of fescues and meadow grass are open to greater disease pressure, and can also struggle in dry conditions too. If your lawn struggles greatly from red thread attacks then a renovation with an improved seed mix would be the best method.

2) Consider your mower

Red thread enters the grass plant via damaged leaves. Cylinder mowers cut the grass in a scissor like fashion, whereas rotary mowers which are popular for lawns cut grass by bashing it and with less cuts per square metre.

If your mower isn't razor sharp in a warm and wet period with plenty of mowing to be done, this will tear the tip of the leaf and allow a simpler passage for the disease. This is common when red thread is rife.

3) Nutrition...

A much debated point. A lawn which receives too much nitrogen per year will be more susceptible to disease pressure. Some lawn care companies and homeowners do just this. Producing lots of lush, 'soft' or leggie growth leaves the plant open to attack. Slow release fertilisers (10 weeks+ longevity) will give a steady source of nitrogen (lawn food), rather than your lawn riding a big dipper. Our lawn treatment programme is perfect for this - utilising slow release nitrogen sources, not available in DIY stores. If we over-ate it would make us ill also.

4) Shade / air flow / aeration

We know that disease enjoys damp, still conditions. Aside from taking a hairdryer to your lawn, consider the surroundings and surface aeration. This will aid disease pressure.

Corrective measures...?

Fungicides do exist to suppress turf disease. This may be important on sports surfaces ahead of a big fixture worth millions where a large budget is in place with the surface tended to every hour.

For lawns it is not something that we recommend, and certainly for red thread. As we know, red thread will reoccur should the conditions present themselves. Following an expensive fungicide application, the disease could return with greater vengeance 6 weeks later. Although some lawn care companies will offer this option - in our opinion it's not worth our time or your money.

The option of masking the disease is the viable short term option until the weather dries up a little. A few ideas:

A nitrogen based fertiliser will help the damaged areas to 'grow out'. The fertiliser will give a colour boost and improve growth. Remember, a drip feed of food is best.

A potassium based fertiliser, maybe with added calcium will improve disease tolerance. However, it's unlikely that your lawn is suffering from a deficiency.

Magnesium and iron will improve the colour of the lawn. Consider a liquid application for quick results over a granular. If applying iron through the winter also, consider the level of iron that is now going to be applied to the lawn - this may impact soil pH. Iron works to dehydrate moss, so be cautious in it's application through summer and it will do the same to grass at a given rate...

What we would do

Our lawn survey considers a range of chemical, physical and biological factors. We advise our customers individually given that no two lawns are the same. If several visits per year from a professional groundsman is going to benefit the appearance of your garden, (and you've made it this far through this post!) then maybe it's a good time to get in touch for a free lawn survey.