wilting cauliflower

One of my cauliflower Graffiti has suddenly started to wilt today in the sun. Is this always a sign of disease? The others are so far fine.

They have collars on and are under fine mesh netting.

Is there a way to tell if it is cabbage root fly (but collars and mesh) or clubroot presumably from infected plants which were bought as plugs. The leaves havent changed colour but one leaf has always been a bit distorted.

Hopefully the former as I use this bed in the spring to grow turnip oasis 

Since the sun has gone in it has picked up a bit. Should i give it a second chance or should i dig it up to stop it causing problems in the raised bed 

I was about o suggest club root.... it has affected some of ours this year, worsened by the hot weather as the roots can't take the strain

I've had this quite often and in my case it often turns out to be an ants' nest under the roots. It happened to a lot of my garlic this year too. The ants seem to like dry soil.

Thank you for this. I am having a real problem with ants thus year and hope that  you are right; I really don’t deserve/want it to be clubroot.
Will water in the morning.