Late spring & early summer is when lawns look their best – in that prime time when light is good, temperatures warm, and before the season’s hottest, driest weather takes a toll. But sometimes the sea of green is interrupted by what looks like patches of pinkish-red. That’s usually a sign that the lawn is infected by a common fungal disease called “red thread.”

Red thread gets its name from the stringy, cottony growths that wind over and through the grass blades. Look closely, and you’ll see that the grass itself isn’t discolored. Rather, the reddish pink comes from the strands that are part of the fungus that causes this disease.

The thready strands, which aren’t harmful to people or pets, look more pink when they’re dry and more red when they’re wet, such as when dew-covered in the morning or after a rain.

Patches in lawn caused by red thread disease
Red thread disease causes patches of stringy, pinkish-red growths in the springtime lawn.
George Weigel

What causes red thread?

The fungus that causes red thread can come into a lawn by wind, water, or on equipment or even shoes that are carrying spores from an already-infected lawn. It thrives in damp or humid conditions when temperatures are between 60 and 75 degrees. That’s why the most common red-thread season is late spring. Growth stops when temperatures hit 85 degrees.

Red thread especially favors fescues and perennial ryegrasses in cool-climate regions and bentgrass and bermudagrass in warmer regions, although it can affect inferior varieties of most any species of turfgrass. The disease also tends to thrive in under-fertilized, nutrient-poor lawns.

Dealing with red thread

The good news is that red thread seldom kills lawns – at least not large sections of it. Fungicides are generally not recommended since hot weather usually ends an outbreak and grass goes on to recover on its own. To speed recovery from red thread, you should collect the clippings from your lawn if the blades are very long when you mow. This will prevent the clippings from smothering the grass and helps the leaves dry out faster, which will slow the growth of the disease.

Top-dressing with compost also discourages red-thread growth. In the long term, overseeding the lawn with quality, disease-resistant grass seed can gradually make the lawn less prone to red thread and other lawn diseases. If a particularly bad outbreak kills any lawn patches, remove the dead turf, loosen the soil underneath to four to six inches, and plant new grass seed.

Though these options will help, the best solution is to add more nitrogen to your lawn. Since red thread is more common in nutrient-poor lawns, one of the best solutions is simply to fertilize with a nitrogen-rich fertilizer, such as GreenView Fairway Formula Lawn Fertilizer. With 63% slow-release nitrogen fertilizing your lawn for up to 12 weeks, it will evenly feed your lawn longer and will keep red thread away.

To completely set yourself up for success, it is best to get on an Annual Lawn Care Plan. This ensures that you are properly fertilizing your lawn throughout the year, promoting a thicker, greener lawn that crowds out room for seeds.