[cronley]

Would appreciate help with lawn black spots in attached photo. My lawn is 30 years old. Black spots started to appear about 6 years ago in one corner of lawn. Now they have spread all over the lawn. The blackness does not seem to be growing on the soil. It seems to be attached to grass stems & leaves. It is a matted thing, with spongy appearance, & slightly slimy/sticky. It is worse in wet weather.
About 3 years ago I put white lime on the blackness. It cured it for a while, but it came back again. March 2012 I sprayed bluestone on moss patches, & scarified the lawn a few weeks later in dry weather. The blackness is not dead moss.
The lawn is not low-lying. It is not boggy. It is on good soil. It has a nice slope for water run-off. It does not show pools of water.
Any ideas on a cure. Any danger it will eventually kill the grass.

[The Garden Shop]

Ive noticed this on lawns last summer and worse cases this summer.

Im not sure either. but it could be a fungal disease called Anthracnose or 'Basal rot'.

Can occur on lawns that are cut very low, where there is poor drainage and soil compaction.

Can you say whether your soil is compacted and if the excessive rain has left the surface continually damp?

If it is Anthracnose, its recommended that you aerate your soil using a garden fork. Work the fork into the ground to a depth of 1 foot and slightly life the soil. Continue to do this across the effected area at 1 foot spacings.

Either way, if its not Anthracnose, it is likely to be some type of fungal disease. To control / reduce fungal diseases you will need to keep grass and soil dry and well ventilated and keeping your grass fed and stress free (less walking on it, don't cut it too short)

[James Kilkelly]

Looks like lawn algae to me cronley.
Commonly found on either compacted, poorly draining, closely shorn, or hungry lawns like The Garden Shop said. Any or all of these conditions.

Spreading granules of lawn sand/sulphate of iron or watering on sulphate of iron or other moss killers will knock it back for a while.
However, if you address the compacted, poorly draining, closely shorn, or hungry issues then you will solve it completely.
Any of them sound like they could be on site?

[cronley]

Garden Shop & James
Thanks for replies.
Did not think lawn was compacted. Only compaction, is me cutting it for 30 years, plus kids growing up, playing on it. Re closely shorne - I have always cut it at 350 mm. Hungry - maybe yes - I only give it one dose of 7-6-17 per year, is this OK/sufficient. Sure, it is continuously damp in current wet summer. Maybe takes a bit longer to dry out in dry weather, because it is sheltered by 2 meter hedge on all sides. Thought drainage was Ok - good soil - on slope- but higher ground behind me - behind me was open fields for 20 years, but in last 10 years there has been housing developement, - so maybe it has caused my site to be generally damper.
I will spray it with Sulph of Iron or Bio Moss Killer. Garden Shop - could you recommend Bio Moss killer. If this does not work, I will spike it with fork, as you suggest. Hard work - I have .15 acres of lawn. Bigger photo attached.
Thanks again - any more comments appreciated