Pest & Disease Factsheet - Red thread

The risk of this fungal infection on sports and amenity turf can be lowered through careful management.

Red thread on lawn grass - image: John Adlam
Red thread on lawn grass - image: John Adlam

Red thread is among the most important diseases of sports and amenity turf, affecting both visual appearance and playing quality. Good turf management practice can go a long way towards preventing it or reducing its severity.

Red thread, caused by the fungus Laetisaria fuciformis, is characterised by elongated red spikes of fungal tissue extending from the tips of infected turf plants that some have likened to antlers in appearance. It is most likely to occur when growing conditions are poor or if the turf is under stress, especially when nutrient levels are low.

It is most common - and likely to be more severe - in cool, wet or damp weather in spring or autumn, and on less intensively managed turf such as amenity lawns, golf fairways and cricket outfields. It is rare on fine turf such as golf and bowling greens.

Research in the USA (Rutgers University in New Jersey) has looked at the role of endophyte fungi, which live non-pathogenically in the leaf and stem tissues of some turf grass species and cultivars, in conferring resistance to red thread and other common turf diseases. Susceptible fescue species inoculated with strains of endophyte fungi isolated from more resistant grasses showed significantly reduced infections.

How to recognise it

On close examination, especially in humid weather, it is often possible to see the flossy fungal mycelium growing among the grass leaves. The red-pink needle-like outgrowths (sclerotia), protruding up to 2cm upwards from the blade tips, give the disease its common name.

Biology

Laetisaria fuciformis is most serious on fine fescues, especially red fescue, but annual meadow grass, perennial ryegrass and bents are also susceptible. Plants become most vulnerable after prolonged heavy rain has leached available nitrogen from the root zone. Growth and infection is favoured by humid conditions and air temperatures of 16-24 degsC.

The red threads that grow from the tips of infected grass are sclerotia - thick-walled pieces of mycelium that break off and can survive for up to two years in soil or thatch layers. In favourable conditions, the sclerotia begin to grow and infect the leaves of grass plants via their stomata.

The disease is usually confined to the aerial parts of the plant and rarely destroys the root system. The fungus can spread rapidly in a plant and the leaves can begin to die just two days after infection. The mycelium often grows over the surface of the turf plants as well as within the tissues. Although the fungus produces spores, the main means of spread is through sclerotia in grass clippings, on machinery or on footwear.

Symptoms

The initial symptoms are small patches of turf in which the sward takes on a "water-soaked" appearance. As the infection takes hold, small circular patches of dead leaves become interspersed among the living plants.

As the disease develops, infected patches become bleached, forming irregular reddish or brownish patches of dying grass up to 50cm in diameter. In severe cases, most of the leaf blades in the patch are killed. Small patches may be widely scattered or merge together to form larger ones.

Treatment: biological control

Specific biological controls are not currently approved in the UK. However, products containing Bacillus subtilis or Trichoderma harzianum have been shown to have some preventive control.

US research has shown the potential of applying symbiotic endophyte fungi, which live in the leaves of certain species and varieties of turf grass. These produce biologically active chemicals (alkaloids) that make the host plant resistant to pests and produce glucanase that break down the cell walls of pathogens. As endophytes are transmitted through seed, it is possible to take advantage of them in breeding for pest and disease resistance.

Treatment: cultural control

- Application of soluble nitrogen products to boost soil fertility will stimulate fresh growth. Avoid over-applying in the autumn, which can make turf susceptible to snow mould.

- Maintain soil pH at between 6.5 and 7.0.

- Keep turf well drained and the surface as dry as possible. Avoid over-watering - do not water in the late afternoon or evening.

- Consider over-sowing with disease-resistant turf grass varieties if red thread is a recurring problem.

- Plant trees and shrubs far enough apart so that areas of turf do not remain shaded for long periods in the morning, allowing dew to evaporate.

- Avoid accumulation of thatch and take care when mowing or working on infected areas not to spread the disease through flying clippings or on machinery or footwear.

Treatment: chemical control

Active ingredient: Iprodione

FRAC code: 2

Formulations: Various including Chipco Green (Bayer), Mascot Rayzor (Rigby Taylor)

Action(s): Dicarboximide fungicide with contact and curative action. Some products are rainfast in one hour and can prevent the build-up of morning dew. Apply after mowing to dry turf. Allow a minimum of 24 hours before the next mow. See labels for other treatment restrictions.

Active ingredient: Pyraclostrobin

FRAC code: 11

Formulations: Various including Mascot Eland (Rigby Taylor)

Action(s): Strobilurin fungicide. Apply at start of disease attack. Do not apply to frozen turf or during drought. Avoid applying immediately after mowing or less than 48 hours beforehand.

Active ingredients: Tebuconazole + trifloxystrobin

FRAC code: 3 + 11

Formulations: Various including Mascot Fusion (Rigby Taylor)

Action(s): Systemic fungicide mixture with protective, curative and eradicant action. Rapidly absorbed into foliage and translocated acropetally.

Active ingredient: Trifloxystrobin

FRAC code: 11

Formulations: Various including Mascot Defender (Rigby Taylor) - retail products include Lawn Disease Control (Bayer Garden)

Action(s): Broad-spectrum fungicide with protective and curative control and good rainfastness.

Fully updated by Dove Associates.

Use plant protection products safely. Always read the label and product information before use.

Dove Associates shall in no event be liable for the loss or damage to any crops or biological control agents caused by the use of products mentioned.


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