Red Thread on Lawns

In this article:

• Diseases
• What are the symptoms of red thread disease?
• What conditions favor the development of red thread disease?
• Top tips for preventing and eradicating red thread disease

The impact of pests and diseases on turf are important as they will significantly reduce the aesthetic value of a lawn or amenity grassland area. In some cases the damage can be extensive, leading to costly repair work. It is therefore better to be aware of the main culprits that could cause damage and how best to prevent infestations, thereby minimizing the potential for turf stress.

Diseases

Fungi are the most common disease-causing organisms in relation to turf, but not all fungi within the soil are harmful. Many are very beneficial and form important functions in relation to organic matter breakdown.

Those fungi responsible for disease are usually termed “pathogenic.” There are many different pathogenic fungi responsible for the individual diseases found on turf, and they vary widely in their behavioral and physiological requirements. Most grow as thread-like structures called hyphae which can come together in large numbers to form mycelium. This mycelium may or may not be visible on the plant tissue of affected plants or within the soil.

In general, most pathogenic fungi are always present in turf but it is only when favorable environmental conditions occur that a disease will develop. Good management can often be enough to keep disease outbreaks at bay; however, the changeable and unpredictable nature of the weather often makes disease control difficult to achieve.

General amenity turf dominated by vigorous perennial ryegrass is less prone to many diseases, mainly due to the less intensive nature of the maintenance, especially at the higher height of cut. However, red thread (Laetisaria fuciformis) is probably the most prevalent disease to affect such areas as well as commonly affecting fine turf areas as well.

What are the symptoms of red thread disease?

1. Grass has a general pink or red appearance turning bleached/light brown as the disease progresses.
2. Fungal growth is visible either as pink, cottony flocks or as small red needles sticking out from diseased leaves. The needle like structures can be up to 25 mm long. They are called stromata and are the survival structures of the causal fungus.
3. Infected patches of grass may be as small as 50 mm in diameter or as large as 350 mm.
4. The fungus causes the grass leaves to die back from their tips but, unless grass growth is poor, damage is generally superficial.

What conditions favor the development of red thread disease?

1. Red thread can occur at any time of year but is most commonly seen in late summer and fall.
2. Red thread disease can be found on any type of turf, but red fescue and perennial ryegrass species are the most susceptible. Different cultivars within these species will also have different levels of disease resistance.
3. As for many turfgrass diseases, a moist surface will aid the spread of disease and excess organic matter will serve to harbor causal fungi.
4. Plants are most susceptible when grass growth is slow due to low fertility, and in particular when there is insufficient nitrogen.

Top tips for preventing and eradicating red thread disease

1. Infected areas should receive an application of nitrogenous fertilizer. This should usually be enough to help the plant grow through the disease. The choice of fertilizer may depend on prevailing conditions, with a liquid being used if conditions are dry and no irrigation is available.
2. Remove clippings from affected areas to minimize the spread of disease.
3. Control organic matter and maintain surface drainage with regular aeration.
4. Maintain a good level of fertility to aid healthy grass growth, particularly ensuring adequate levels of nitrogen are available throughout the season.
5. Overseed using cultivars with a good tolerance to red thread infection.