The most common and damaging pathogen on ornamental lawns and sports turf in the UK is the fungus Microdochium nivale (syn. Fusarium nivale). The disease it causes was traditionally known as snow mould because it was most often associated with cold, wet weather in spring, with damage typically revealed when snow cover melted. However, the fungus can damage turf whenever conditions are cold or frosty and wet. It has now become much more common in autumn than spring and is known as Fusarium patch when its appearance is not correlated with snowfall.
Despite the damage it can do, Microdochium nivale is a fairly weak pathogen. It grows on organic material around the base of the sward until conditions favour infection. Removing thatch, creating good drainage and avoiding overfeeding are vital first lines of defence. Recognising early symptoms is also crucial for control before too much damage is caused.
Fungicide application must be correctly timed in relation to weather conditions that cause the greatest disease risk. The recommended water volumes must be used for systemic fungicides to enable the product to penetrate the root zone and be taken up. Reducing volumes may speed application time but can compromise efficacy. Damaged patches take a long time to recover after treatment. Fungicide resistance has not so far been reported in the UK, although it has appeared in the USA and New Zealand. Alternating sprays from different fungicide active groups should reduce resistance risk.
How to recognise it
The fungal mycelium is pale pink and, when massed together, lends a distinctly pinkish tint to the surface of the affected turf, especially at the edge of an infected patch, where the fungus is actively growing and producing spores.
Snow mould and Fusarium patch are essentially the same disease and caused by the fungus Microdochium nivale. Optimum growth temperature is 1-10 degsC. Some strains grow well below 0 degsC. Growth of the species is inhibited above 20 degsC.
Microdochium nivale grows on dead material in the thatch layer until conditions enable it to infect living turf. Infection is favoured by cool, wet weather or frost alternating with cold and wet. Infection only takes place after prolonged periods (at least 10 hours) of leaf wetness, which enables the windand water-dispersed spores to germinate, producing hyphae that enter the leaf through stomata and wounds. Bents and fescues are susceptible. Annual meadow grass is especially susceptible.
In the early stages of infection, individual grass plants start to become slightly paler in colour. It progresses to produce small patches (about 2cm in diameter) of dark-brown or olive-coloured grass with dark, slimy or water-soaked leaves.
Infection spreads to form patches 30cm or more across with brownish or greyish dead grass in the centre. Grass at the edge of the patch is water-soaked or slimy, with white or pinkish mycelium matting the leaves together. The pink mycelium is often easiest to spot early in the morning.
If allowed to spread unchecked, individual adjacent patches merge to form large, irregular infected areas.
Treatment: biological control
- Trials in the USA (Washington State University) have found isolates of naturally occurring Pseudomonas bacteria can reduce disease development on turf grasses, including annual meadow grass.
- Drenches of Revive P or specially formulated compost teas (XL Horticulture) will increase beneficial micro-organism numbers and subsequently increase competition for space on root and stem surfaces.
Treatment: cultural control
- Prevent the base of the sward remaining wet by ensuring adequate drainage with regular scarification and aeration treatment.
- Remove and prevent thatch, which harbours the fungus and retains water and humidity.
- Use acidifying fertilisers and aim for a pH of around 6.5.
- This pathogen prefers alkaline conditions. Iron sulphate acidifies the surface and hardens the leaves, making them less prone to infection.
- Applying high-nitrogen fertiliser late in summer or going into autumn causes lush growth that is more susceptible to attack.
- Keep grass short going into winter.
- On fine greens, brushing to remove dew is worthwhile. The risk of spreading spores is outweighed by the benefits of removing the conditions they need to germinate.
- Time irrigation to pre-dawn or early morning to knock dew off leaves.
- Apply a dew-control product such as Dewcure (Headland Amenity).
- Judicious pruning of overhanging or adjacent vegetation to reduce early morning shade and increase air movement over the surface helps to dry turf more quickly.
- Good aeration, balanced nutrition, regular scarification and prompt attention to surface drainage problems encourage good microbial diversity in the root zone, which helps to reduce thatch and organic matter on which the pathogen lives.
- Soil microbial diversity can also be encouraged by biostimulants such as seaweed-based fertilisers and compost teas.
Treatment: chemical control
Active ingredient Azoxystrobin
FRAC code 11
Formulations Various including Heritage (Syngenta)
Action(s) Systemic, translaminar fungicide with eradicant and protectant abilities. For best results, use as a protectant or during early stages of disease establishment.
Active ingredients Chlorothalonil, fludioxonil and propiconazole
FRAC codes M5+12+3
Formulation Instrata (Syngenta)
Action(s) Protectant and systemic eradicant action. Long-lasting effect with rapid leaf uptake.
Active ingredient Iprodione
FRAC code 2
Formulations Various including Chipco Green (Bayer)
Action(s) Protectant fungicide with some eradicant ability. Apply after mowing to dry turf free from dew. Allow 24 hours before next mow. May cause temporary yellowing if frost follows treatment.
Active ingredient Pyraclostrobin
FRAC code 11
Formulations Various including Insignia (Vitax)
Action(s) Protectant, curative and eradicant action. Apply at early stages of disease. Do not apply to frozen turf or during drought. Avoid applying immediately after mowing or fewer than 48 hours before.
Active ingredients Tebuconazole + trifloxystrobin
FRAC codes 3 + 11
Formulations Various including Fusion (Rigby Taylor)
Action(s) Combination of active ingredients provides protectant, curative and eradicant action. Apply at early stages of disease establishment.
Active ingredient Trifloxystrobin
FRAC code 11
Formulations Various including Mascot Defender (Rigby Taylor)
Action(s) Protectant and eradicant action. Apply at early stages of disease.
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.