Today, we've had some really good weather for growing tomatoes. Lots of hazy sunshine with a nice floating cloud or two for the odd bit of temporary shade.
I think the biggest threat to my plants at this time of year is damp wet air. I can keep them out of the rain but I can't control the humidity or condensation which can be almost as bad as rain, especially if they are slightly over-watered.
The only moisture that I like on tomato plant leaves is when spraying a mist of water to foliar feed or to revive a plant that has been in hot sunlight and has started to wilt.
It is a "given" that tomato plants hate wet leaves, that is leaves that are wet for more than a few hours, which may lead to fungal diseases such as damping-off (when seedlings shrivel and die) or tomato blight on older plants.
Fugal spores may also be found in compost that has been left in the rain outside a garden center from last season - try to make sure that the compost you buy is this year's supply.
More information about growing tomatoes may be found on the tomato growing tips page.