Collapsing lettuce

[roitelet]

I have two cold frames which are kept open all the time now. both contain lettuce.
In one of them I have had lettuce suddenly collapsing one at a time. Cant find any sign of beasts and the base of the lettuce looks as if it is rotting. No sign of botrytis either. They are kept a bit on the dry side to avoid rot.

Any suggestions please?

[Nicos]

Overheated?
I find my butterhead lettuce do that later on in the summer.....

[roitelet]

Don't think so, the tops are off all the time. The lettuces seem to go down one at a time as if some critter does for one and then moves on to the next, but I can't find the beast! Also it is only happening at one end of one frame. Mystery!

[Snoop Puss]

Dig them up and transplant them out into a bed if they're not too big for that.

[roitelet]

Cant do that they are just about eating size and they collapse over night.

[Zelenina]

How dry is "a bit on the dry side"?

I find the most common cause of plants suddenly collapsing is shortage of water, especially if the weather is hot too. I expect it's getting quite hot now where you are.

Lettuces in particular can't tolerate drought. But if you catch them soon enough and water them and leave them in a cool place for a while they'll usually recover, if that is the problem.

[roitelet]

They are damp and I don't think it's a water problem. The base of the plant has rotted but I can't make out if there was insect damage first. They are also collapsing one at a time the others look fine

[Scarlet]

Something eating the roots?