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( Monographella nivalis syn. Fusarium nivale )

A patch of Snow Mould affected grass after a period of snow cover.

A fungal disease which attacks lawns. Infection usually occurs at temperatures between 0C and 8C, conditions which are present under snow giving it the common name of Snow Mould.
If conditions are present it can appear later as irregular patches of yellow then brown grass up to 30cm in diameter when there is high humidity and temperatures of up to 18C. This usually occurs between May and September, when damp conditions prevail. The dead blades of grass become slimy and are covered in a light-pink bloom. It is transmitted by wind-borne asexual spores and the dormant phase is as mycelium in dead leaf matter where it rests during frosty or dry summer conditions.
Infected material can be carried on tyres or shoes to spread the disease.

To prevent infection:

Avoid using high nitrogen fertilizer in autumn as it produces lush growth in autumn and winter which is highly susceptible. Thatch in the grass creates the humid conditions required for development of the fungus so autumn scarifying should halt it. Avoid walking on the grass if it is covered with snow. The more dedicated lawn keeper would go out in the morning to remove a heavy dew with a flexible rod or cane. A good flow of air at ground level allows the grass to dry more quickly after rain, so pruning overhanging trees and shrubs should help.

Only one fungicide is available for use by the amateur gardener, trifloxystribin sold as Bayer Garden Lawn Disease Control in the UK, but to avoid resistance developing it should not be used more than twice in one year. A systemic fungicide such as Carbendazim which kills the mycelium would also work, but due to EU regulations it is only available for professional greenkeepers to use in UK as a treatment for lawns.

Similar dead patches can be caused by dog urine, but if you don't have a pet Red Thread could be the cause. Slime Moulds are completely different organisms, although the blades of grass become slimy.

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