Fusarium patch is one of the most common fungal diseases of the lawn. It is caused by the fungus Microdochium nivale and is often found during autumn, winter and early spring. It is a damaging disease and can be difficult to cure. 

The disease first appears as small patches of yellowing grass which increase in size, often merging with other patches to form large brown areas where the grass has been killed. In damp weather, the edges of the diseased areas may be covered with a fluffy white or pale pink mould.

Infection often occurs in summer but goes unnoticed, hidden by the rapid growth of the grass. As temperatures start falling and growth of the grass slows down, the disease becomes more evident. The fungus requires surface moisture to infect leaves, humidity and dampness of the grass are ideal conditions for this disease. These conditions may be exacerbated by high nitrogen levels which can lead to both imbalances in the soil and growth of the grass which is susceptible to disease at this time of the year. This fungus is particularly aggressive during periods of prolonged compacted snow cover. A fairly constant temperature and increased levels of carbon dioxide under the snow allow Microdochium nivale to flourish. 

An outbreak of Fusarium is a sign that the conditions of the lawn need improvement, and prevention is far better than cure. Chemical treatments can do more harm than good, the focus should instead be on good practice in lawn maintenance. Soil conditioning and an improvement of airflow above and below the surface of the soil help build an inherent resistance within the lawn. Excessive shade from trees and shrubs often lead to moisture retention, inviting fungal activity. Similarly, the removal of heavy dew in the mornings can be effective in improving overall dampness and maintaining a lawn free of Fusarium. 

Regular aeration and scarification treatments tackle soil compaction, boost drainage and improve air circulation to help build resilience. Low-nitrogen, high-potassium fertilisers during autumn strengthen the grass without encouraging new growth. Keeping the grass at the appropriate length for the time of year, ensuring mower blades are sharp, trimming trees and shrubs to increase airflow all help keep Fusarium under control.