Fusarium patch

Microdochium nivale

also called snow mold, Microdochium patch

Small water-soaked patches of lawn that turn brown and matted, often ringed with white or pink cottony mold; the commonest and most damaging turf disease of cool, wet spells.

Fungus Serious Airborne sporesSpread in waterSpread on tools & hands Spreads to neighbors

What you'll see

Round patches of grass turn yellow, then brown, and look water-soaked at first.
A white to salmon-pink fluffy mold rings the patch edge in damp weather.
Patches start small and can merge into large slimy dead areas.
Grass mats down and the patches feel greasy underfoot.
Damage often follows a thaw or a long cool, wet spell.

Why it happens

Fusarium patch is caused by the fungus Microdochium nivale, long known as snow mold because it often shows up as snow melts. It survives in thatch and debris and spreads on water, air, mowers, and feet.

It strikes in cool, wet, still weather in autumn, winter, and early spring, and is made far worse by lush, soft growth from late high-nitrogen feeding and by shade, thatch, and poor drainage.

Treating it

Improve airflow and drainage, and switch the water off, as the disease needs prolonged wetness.
Brush off dew in the morning to dry the leaf surface.
Collect and bin clippings and avoid feeding with high nitrogen while it is active.
Scarify out matted dead grass and reseed bare patches once conditions improve.

Keeping it away

Avoid soft late-season growth by holding off high-nitrogen feed after summer.
Use an autumn feed higher in potassium to toughen the turf.
Reduce thatch and aerate to keep the surface drying quickly.
Cut back overhanging growth to let in light and air, and clear fallen leaves.

Who gets it

Lawns and fine turf, especially annual meadow-grass and lush, shaded, or poorly drained swards.