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Evident in cool wet conditions from late autumn to spring.
Fusarium or fusarium patch is the more common of the two lawn problems whilst snow mould is exactly the same disease that occurs after prolonged snow cover. Fusarium is primarily a disease of fine or old turf generally occurring in the late autumn during prolonged damp weather and also in winter usually during a mild spell. It can be damaging because it kills the grass plants though you may end up with small infestations and not notice it.
If you do notice it you will see small tennis ball size straw coloured spots. These get bigger in the right conditions. Whilst the disease is growing the perimeter has a slimy coating of whitish fungal mycelium. This can make the patches irregular in shape looking like fluffy clouds.
As the disease generally strikes in cool weather with constant moisture (drizzle or fog), turf with a heavy thatch layer, compaction, poor drainage, clay soil or shade is more prone to attack. Late and heavy applications of nitrogen fertiliser can make the grass plant more susceptible to the disease.
New lawns can also suffer particularly after snow. This is primarily because they are still relatively tender and have not built up much resistance to disease and fungal attack.
Prolonged compacted snow cover will often cause an outbreak. You can reduce the chance of snow mould damage by NOT throwing snow on the lawn from paths and driveways and removing snowmen and snowwomen once they’re finished with.
If you do get an outbreak you should treat it as a wakeup call that the lawn conditions are not the healthiest. Fusarium treatment should include inspection for thatch, scarifying as required (when conditions are right - usually March onwards) and hollow tine, slit or spike to improve drainage.
Remove clippings after mowing and ensure the autumn fertiliser treatment is slow release nitrogen with a good amount of potassium such as Lawnsmith® AUTUMN Lawn Feed. This should be no later than November in the south or October in Scotland. More importantly, late autumn and early winter applications of Ferrous Sulphate (Soluble Iron), typical in the sports turf industry, will harden the turf thus helping protect it from such diseases. Alternatively use a combined iron fertiliser such as Lawnsmith® WINTER GREEN High Iron - a fertiliser blended specifically for hardening turf and ideal for application in late autumn and winter.
You still need to adhere to good lawn management as above but you can treat fusarium with a fungicide. You are going to need to be on the ball as treatment prior to attack is the best way to control this disease. Treat too early before an attack or using it 'just in case' means the fungicide usually runs out of steam and therefore has little effect if and when the disease gets going and of course, treating too late defeats the object. This means the skills of a green keeper are required to assess the correct time to apply which makes treatment a problem! Add to that, you may need to treat several times in a year and as treatment prevents the grass building up its own resistance to the disease you'll get locked into an an annual cycle of treatments!
I rarely see fusarium in lawns of the severity that require fungicidal treatment but if you have a valuable lawn and the soil or lawn conditions make your grass prone to the disease then fungicide could be considered though preference should be given to addressing the cause rather than getting into a never ending cycle of fungicidal applications.
Please also be aware fungicieds may kill helpful fungi and bacteria in the lawn, some of which help decay thatch and breakdown organic matter into plant food.
Should you suffer an attack which leaves considerable damage (new turf can suffer badly) it’s worthwhile helping the lawn recover otherwise you may well find the patches invaded by weeds and weed grasses! Do this in the spring NOT before:
Do NOT add soil or peat to cover the seed as you will create a bump in the lawn. If you feel some covering is worthwhile us pegged polythene, plant fleece or a light covering of straw which can be removed after germination.
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