Curling tomato foliage

Can anyone tell me why my tomato plant leaves curl up? I have two varieties in the greenhouse. The plants of Shirley are healthy, disease free with dark green foliage and a late but decent crop, but with Moneymaker its a different scene; the leaves are pale and curled. There doesn't seem to be any pest present, but the crop is weak.

Sounds like a silly question but are the leaves curling up at the edges or down at the edges? The difference usually leads to different diagnoses.

Just to expand a little on the above. Leaves curling downwards at the edges is most often a sign of some sort of contamination by herbicide. Leaves curling upwards is much more common and there can be a number of causes.

Excessive heat can cause it. My toms in the ground are covered with curled leaves because we're into about our third week of high-30sC. It's just the plants' stressed reaction to the heat.

Excessive watering can cause it, particularly with container plants. Pale foliage is another symptom.

Pests - aphids, white fly, etc - can cause it.

Disease can also be a cause. Is there any evidence of disease - specks, spots, whatever - on the foliage? And is the affected foliage old foliage? New? Or are the symptoms all over the plant?

Italophile thank you for your detailed reply. All the folige is affected there are only two trusses and they are poor because of the cold in early summer. There is no sign of aphids or whitefly, just small plants and overall pale leaves. I have watered less this year so I dont think it is overwatering. Someone said it could be the cold.

Yes, they can react to cool weather too. How often are you watering? I'd knock off the watering completely for a while to see what happens. The plants won't suffer if the weather is cool.