Following enquiries requesting help with diagnosing sickly-looking lawns, this week’s technical article, written by BALI's Technical Officer (Policy & Research) Owen Baker, will discuss one of the more common lawn ailments, Fusarium.
What is it?
The most common disease of turf in the UK, according to BALI Registered member Harrowden Turf.
The Latin name for this fungus is actually Microdochium nivale, but a former Latin name was Fusarium nivale – hence the name you are likely to hear most: Fusarium patch. The fungus may also be referred to as ‘Snow mould’ due to the fact it is often seen after snow has thawed from a garden.
Three turf grass species commonly grown in the UK are susceptible to Fusarium: Annual meadow grass (Poa annua), perennial ryegrass (Lolium perenne) and Creeping bent (Agrostis stolonifera). These grasses are commonly found in domestic rolled turf, golf courses and bowling greens.
What are the symptoms?
Fusarium may first be identified by small (1-2 centimetres) orange/brown patches of turf. Over a period of a few weeks, the size of these patches may grow, join together and form much larger areas of bare ground. Sometimes, and particularly during wet weather, white/pink coloured mycelial growth will develop around the edge of the bare patch.
Why does it appear?
Fusarium spores and mycelium are abundant throughout the landscape, year-round, but are more likely to produce symptoms in certain conditions. The disease requires moisture on the surface of the grass in which to grow and consequently, when the grass stays wet for longer periods, with a temperature of between 12 and 19oC, symptoms are most likely to manifest. For this reason, the disease is likely to be most active in autumn.
Fusarium is not active in temperatures above 20oC or when the surface of the grass sward has insufficient water. Consequently, Fusarium is not normally active during the summer, and faster grass growth during this period makes symptoms less obvious.
As stated earlier, the disease may also be referred to as Snow mould. The reason for this is that, beneath a layer of snow, the fungus will thrive in a carbon-dioxide-rich environment with constant temperature. When the snow thaws, large areas of damaged lawn are likely to be visible.
Fusarium initially attacks the outer cell walls of the grass plant. Lignin, a component of cell walls in all plants, acts as a barrier to plant pathogens. It is present in higher quantities in mature plants and less so in younger plants. Consequently, young grass found in new turf is more susceptible to Fusarium. Fresh growth encouraged by application of fertilisers is also more vulnerable to Fusarium attack, which means applications should be timed so as to avoid a higher risk of attack.
How do I control it?
In most cases, diseased turf will recover once the grass is growing between spring and autumn. Fusarium growth can be discouraged by ensuring the grass sward is kept short, which will encourage greater air movement between leaves and a dry surface. Similarly, heavy thatch layers should be removed to aid drainage and encourage air circulation.
Well-structured and free-draining soil beneath the turf will also avoid the damp, humid conditions which favour Fusarium. Compacted or soils with poor drainage should be improved to discourage attack.
Trees and shrubs which over-hang turf and encourage damp, shaded conditions should also be avoided.
Chemical control may be undertaken in the form of preventative, curative and combined fungicide solutions.