Fusarium & Snow Mould

Evident in cool wet conditions from late autumn to spring.


Fusarium Patch – Image Courtesy STRI

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 and in to winter usually during a mild spell. It is not particularly common in lawns but can be damaging because it kills the grass plants. 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.

The disease generally strikes in cool weather with constant moisture (drizzle or fog). Consequently 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.

Remedy 1


Snow Mould

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) 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 mid October in Scotland. More importantly, late autumn 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.

Remedy 2

You still need to adhere to good lawn management as above but you can treat fusarium with a fungicide. 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.

Repairing Damage

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:

  • Rake patches to clear dead grass and expose the soil
  • Densely spike patches around 1/2″ deep
  • Add matching seed at 10 to 20 seeds per square inch
  • Brush then tread seed in
  • Fertilise patches if not doing the whole lawn
  • Keep damp
  • Mow on the high side with sharp baldes for the first 2-3 months

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 or a light covering of straw which can be removed after germination.