Question
Hello Ronald,
I read your explanation about fungi with interest. My friend has recently applied weed and feed to his established lawn, twice within a relatively short period. And the other day when he fertilised it with a high growth fertilizer, it went yellow.

So it seems the bad fungi have taken over.
Would you tell me how to fix this please ?

Regards
John

Answer
Two applications of a plant killer (the 'weed' component of the W&F product) by itself can cause the desirable grass to die. At the same time he is putting down two applications of (probably high) Nitrogen fertilizer (the 'feed' component in a W&F product). Then he proceeds to put down   an additional (probably high) Nitrogen fertilizer by itself.
By this time the turf might just wish to just die!
I cannot say for sure what the problem might be; but I think that the turf is heavily stressed from the effects of what has been done to it in such a short time. All I can suggest is watering regularly and adequately. You want the water to soak into the soil - NO runoff! As soon as water starts to run off on to the street or sidewalk, stop the watering. Water early enough to enable the grass leaves to dry completely before the sun goes down. Preferably, water in the mornings.
Hopefully this will help the grass to recover.