White cottony fungus on my lawn – what is it? (Microdochium / Fusarium patch)
Spotted this on my lawn this morning while the dew was still down. White cottony stuff webbed through the blades. Once the sun came up it pretty much disappeared. Anyone know what I’m dealing with?
Most likely early Fusarium patch.
The white cottony mycelium webbed through the blades is the active fungus. You'll typically only see it while there's dew on the lawn or during wet, overcast weather. Once the surface dries it disappears.
The fungus survives summer in thatch, then reactivates when things cool down. Autumn through into winter is its main window in NZ. Cool damp nights with the lawn staying wet through the morning are exactly what it wants.
Make sure you're not watering at night or in the evening. Keep nitrogen moderate going into autumn, and avoid fast release fertilisers. Only mow when dry.
This is early stages so you'll get good 28 day preventive with NZLA Azoxy. The longer you leave it the harder it is to knock back. Fungus Pro is a good contact but it's useless once washed off, unlike Azoxy, so if the conditions aren't improved asap I'd be leaning towards Azoxy.