Mary Evelyn said:
Hi Alan,
These are the pics we took tonight at 5.30pm, after work.The trees involved and the fungi.I have left the grass to grow for a few weeks because of the fungi.I would be very grateful for your help.
Hi Mary,
I think we have to go with possibility number three, that the fungus is nothing to do with the tree, nor with your previous treatment of the lawn.
The photographs need a bit more definition, but the tree appears to be an Ash, and Ash forms mycorrhizas only with a small group of microscopic soil fungi, not with any toadstool species. Nor do the fungi look like any parasitic species.
It would be good to see the gills - I should have suggested that one of the toadstools was picked and turned over before the photographs were taken. However, although the focus isn't great, your fungus looks like it is
'Fairy-Ring Champignon' (Marasmius oreades).
The gills should be pale cream in colour, rather thick and widely spaced, and the whole toadstool should be tough and rubbery. It is a frequent species of lawns and short grass, especially in summer and early autumn, and yes it does grow in very distinct rings.
It is almost certainly the cause of your brown circles in the lawn. It causes complex chemical changes in the soil, sometimes stimulating grass growth, sometimes killing it. I have a book on fungal diseases of amenity grasslands and Fairy-Ring Champignon gets several pages devoted to it!
The bad news is that control is very difficult. General fungicides will not work and the few chemicals that seem to have some effect are themselves highly toxic or carcinogenic. The best general advice seems to be to keep the lawn damp - it does better in dry conditions.
The fungus will probably vanish in time in any case.
It is, incidentally, a highly regarded edible species, but there are some quite similar fungi that are highly poisonous and which also grow on lawns. I am not in much doubt about my suggested identification, but I will not be 100% definite from these photographs.
Hoping this helps!
Alan