Fusarium / Microdochium Patch / Pink Snow Mould
Fusarium is a turf disease that is caused by a fungus called Microdochium nivale. It is often found in fine turf situations, such as bowling greens, but can appear on lawns, particularly after prolonged snow cover. In such instances it may be known as Pink Snow Mould.
Good soil fertility is the key. High levels of nitrogen can increase incidence and this is one reason that TruGreen® lawn care specialists use autumn/winter fertilisers containing low quantities of nitrogen in the spring and autumn periods.
The conditions during which the disease is most vigorous are high humidity, surface wetness (rain, dew, poorly timed and frequent irrigation) alongside cool temperature.
Disease symptoms can appear as small circular patches which first appear as water-soaked spots under 5cm across. Grass colour will change to orange – brown, moving on to a darker red-brown which sooner or later becomes a tan / straw colour. If the disease goes unnoticed it can start to spread in lines because spores can be spread by mowing. Spots of Fusarium often merge to form larger areas of disfigurement.
After snow cover, the fluffy white mycelium fungus can be found on matted grass leaves and the affected grass looks straw coloured with a pink tinge. Fusarium survives over the summer months because it rests on grass debris such as grass thatch. When favourable conditions return, the pathogen will infect leaves of living plants. Under wet, cool conditions, it will spread quickly due to the large numbers of conidia spores. Conida spores are produced asexually which means uniformity and large numbers being produced. These spores will be spread be mowers, feet and wheeled equipment.
There are several factors that can make it easier to predict the likelihood of incidence.
- Humid atmosphere, shade and wetness when accompanied by cool temperatures.
- Inadequate circulation of air above the grass sward.
- Rapid, forced, weak top growth in spring / autumn.
- Alkaline soil pH, 7 – 14.
- Weak turf, perhaps due to wear or irregular mowing.
- Blunt mower blades causing a poor cut.
- Compacted soil. and poor drainage.
Outbreaks can be reduced by a number of means.
- The practise of cultural control methods such as aeration and scarification.
- Regular mowing
- Alternating the direction of the cut helps the grass stand upright this will also help air move between the plants.
- Lowering nitrogen applications at the end of the summer / early autumn period.
- For the most enthusiastic gardeners, they can play a role by removing dew with a rake in the mornings.
