How to treat red thread lawn disease?

Have you noticed the presence of odd red threads in your lawn?

These are signs of a fungal infection caused by Laetisaria fuciformis. This pathogenic fungus, which lives in soil, thatch and dead leaves, feeds on the nutrients it steals from your lawn.

How red thread disease develops and spreads

Red thread disease can occur at any time of the season, between March and November, and at temperatures ranging from 5 °C to 30 °C. However, it most often develops in damp, cool weather in spring or fall, when temperatures vary between 15 °C and 24 °C.

As with fungi, the disease spreads when spores are carried from one area to another by wind, air, water or even humans.

The speed at which the disease develops depends, among others, on the quality and compaction of the soil. A lack of nitrogen and a compacted soil structure will accelerate its spread.

How to recognize red thread disease

Red thread is recognizable by the presence of red to yellow spots ranging from 2 to 30 cm in diameter. Reddish filaments may emerge above the lawn. The red colouration spreads from the top to the crown of the plants.

At the first symptoms, the disease can be confused with other lawn problems (drought, insects). The appearance of small, irregular, yellow-brown spots with a diameter of a few centimetres suggests that the grass is dried out.

The appearance of pink or reddish mycelial filaments or red mucous masses, more visible in humid weather, confirms the presence of the fungus.

At first glance, the blades of grass may appear red. However, upon closer inspection, the blades appear branched and forked, as if shredded. In very humid weather, pinkish or reddish cottony masses appear between the filaments. This is the mycelium.

Which lawns are more prone to the disease?

Red thread disease affects virtually all varieties of turf grasses, but some, such as fine fescues, are more susceptible.

Generally speaking, lawns growing in compacted or degraded soil, which hinders root development, are more prone to disease. To resist disease and remain vigorous, a lawn must be established in soil that is rich in organic matter.

If your lawn grows on poor, compacted soil, aerate annually and add enriched lawn soil to provide the essential nutrients your lawn needs to stay healthy. This topdressing technique allows you to gradually improve your soil without having to start from scratch.

Learn how to do it in this article.

New lawns are also susceptible to disease. Since they don't yet have a well-established root system, they don't absorb nutrients as well. The disease takes advantage of their weakness to quickly spread.

PRO TIP: Before seeding, repairing the lawn or laying sod, pre-apply our Starter Lawn Food 10-20-5. It promotes rapid root growth to better resist disease. It also provides a slow-release fertilizer that feeds the lawn over an extended period.

What is the main cause of red thread disease in lawns?

The main cause of red thread disease is a deficiency in nutrients, particularly nitrogen.

The following factors also make lawns prone to fungal diseases:

Poor maintenance (irregular mowing, inadequate fertilization, infrequent aeration)
Poorly drained soil where water accumulates, encouraging the growth of fungi and disease
Overwatering (the lawn remains constantly wet) or inadequate watering (too frequent and shallow)
The choice of turf grasses (some varieties are more susceptible to disease)
The lawn is mowed too short, which weakens it
Nitrogen deficiency
The presence of pests that weaken the lawn by attacking its root system
The presence of excessively thick thatch that prevents water, air and nutrients from penetrating

How to eliminate red thread disease in a lawn

Regular maintenance and the addition of quality fertilizer enriched with nitrogen can often overcome an infestation of red thread disease.

Fertilize your lawn as soon as you notice the presence of the disease with a nitrogen fertilizer such as our SO-GREEN Perfect Lawn Fertilizer 33-0-3, Triple Play Lawn Food 33-0-3 or GREEN-UP Liquid Lawn Food 30-0-0 for a quick and easy solution (fertilize while watering!).

Also check out our calendar to ensure easy and effective maintenance throughout the season.

Because red thread disease doesn't affect its roots, the grass stops growing but usually doesn't die. By using a fertilizer with the right nitrogen content, growth will resume when the humidity level drops.

A few days after fertilization, you’ll see virtually no traces of the disease... except for bare spots that will need to be repaired.

PRO TIP: Avoid fertilizing during periods of intense heat or drought. Wait until temperatures return to normal to avoid stressing your lawn further.

How to prevent red thread disease in a lawn

Although dry weather slows the growth of the fungus, the conditions that favour its development must be corrected in order to stop the disease.

10 tips to prevent red thread disease

Aerate to reduce soil compaction
Dethatch if the layer of thatch is more than 1.25 cm thick
Fertilize with a quality fertilizer to avoid nutrient deficiencies, particularly in nitrogen, phosphorus and potassium
Water your lawn deeply once a week (vs. light waterings several times a week)
Avoid watering in the evening or at the end of the day (by watering in the morning, your lawn has time to dry before nightfall)
Use a quality grass seed mix containing disease-resistant grasses
Prune trees and shrubs to improve air circulation at the base of very dense plants and to let the light in
Add lime to balance pH when needed (you will know this by doing a soil test)
Improve drainage by modifying slopes, filling depressions, improving water evacuation (gutters, etc.)
Repair thin areas (quickly dispose of infected plants if you see any)

PRO TIP: Don’t forget to fertilize in the fall. One last feed with a high-potassium fertilizer, such as IRON+ Fall Lawn Food 12-0-18, IRON+ Winter Guard Fertilizer 22-0-12 or SO-GREEN Lawn Winterizer 12-0-18, strengthens the cellular structure of turf grasses and makes them more resistant to disease the following spring.