poorly parsley

Both flat and curly parsley have whole sections that are turning a pinky yellow and then dying off. The new growth on the curly parsley looks OK but the flat leaf is wretched.

I had thought that it was low light levels but it has continued to happen despite the recent nice weather.

or overwatering 

Parsley belongs to the same family as carrots and parsnips, and is therefore also vulnerable to carrot fly - I've got five flat-leaf parsley plants and all but one of them is now struggling - it's only a guess until you (or I!) pull one out and look for the tell-tale little maggots but I rarely go through a whole year without at least one plant being attacked, weakened, or even killed.

(The only other problem I've ever had is when I grew them in full sun - not been a factor this year though!) 

Here is a site with some information about the life cycle and control options - in my experience carrots can be completely ruined by carrot fly so I net mine with enviromesh to make sure, parsnips can get a bit manky and cankerish around the shoulders but I put up with it, parsley I usually also leave to get on with it although I am quite taken with the grass mulch idea...........

Not entirely sure about that - certainly any remaining larvae will hatch out into flies next year which could potentially start laying eggs again, but then again Parsley is a biennial so will run to seed quite quickly next year so you will have to start again anyway.

If you do start off more parsley, do let the old plants flower. The flowers are especially attractive to parasitic wasps and hoverflies which are natural predators of a lot of the bugs we don't want!

Thank you for this suggestion; I will certainly let them flower. Any thing planted in my garden has to earn its place by either being friendly to wild life or being good to eat. I love the idea of a plant that can do both