What causes the leaves on a tomato plant to curl?

I have 2 tomato plants , each in it's own container, blk plastic 12 to 14 ins. deep , 1 plant ,the leaves are curling upward , the other plant is fine, they both have exactly the same soil and the same growing conditions [ water and light]

What causes the leaves on a tomato plant to curl?
It is caused by a little bug called a "thrip"


Get some orthene powder and put some around the


base of the BOTH plants and mix into the soil.


Then wet the ground pretty good but have no run off.


Then mix 3 teaspoons of orthene into a gallon on water


and spray the plants every 10 day.
Reply:cut the leaves off if they are male leaves (no blossoms). they are just taking extra nutrients away from the rest of the plant.


They could be curling because of water or drought, sunlight, or they are as mature as they will get.