[sion01]

My basil plants which are outside have got a lot of leaves that have turned black and slimmy and they just disintigrate when they are touched.Any ideas to what it could be?

[mumofstig]

they sound as if they've been frosted 

[Yorkie]

That was my first thought too, but it's hard to credit given that it's August.

I wonder whether it could be a fungal infection?

[sion01]

I dought frost.It's been really humid for a week or two.

[Yorkie]

Have the plants been sat in water / watered a lot?

[sion01]

Yes I hadn't noticed that the pots were sopping wet.I've moved to a nice warm dry plastic greenhouse.I hope I haven't killed them