Have you seen leafhoppers or other possible vectors for other viruses?

The transition from spring conditions to summer conditions is when plants are most likely to show leaf roll and other physiological issues. Unfortunately, it's also when plants infected with BCTV start to manifest symptoms, which develop more rapidly in warmer conditions.

IMO, it's too early to definitely tell what's going on.

If I were in your shoes, I would watch new growth carefully. If other new growth looks normal going forward, it's fine--physiological or possible very slight herbicide exposure. If new growth continues to be distorted and stunted, then you probably have a virus. For peace of mind, I'd probably move the affected plant to a different area of the yard, even though it's not that common for viruses to spread to other plants once they've been detected and in the absence of the pest vectors.

Let's see what others have to say.

I haven't seen any insects around the plants. The leaves seem to grow out of the curly stage after a while, but I'm still unsure about the whole thing.

So it's more than just that one branch? Can you post a picture of some leaves that have grown out of the curly stage?

I am growing the plant as a two stem. The curly leaves are only on the smaller and younger stem. It does seem that the leaves grow out of the curly stage. Here are some more pictures.

I hope these pictures help.

Are those dark spots/squiggles on the affected leaves in that first pic? If so, I'm afraid you probably have TSWV. Compare to pics here: http://tomatoville.com/showthread.php?t=1519

Also, junkgson, please add your location to your profile.
Your Houzz > Edit Profile > Advanced Settings > scroll down to the field Climate Zone for Garden Forums

Don't just enter zone but also your geographical area, as zone 8 in the Pacific NW and zone 8 in the Southeast are very different growing conditions.

The leaves do not have black spots. I think it may just be the lighting.

I heard that these virus will start affecting the plants in a matter of days (I noticed the curled leaves on Friday April 27 after a week of hot sunny weather.), but no other foliage is effected though.

Viruses typically affect only the foliage that grows after infection. What does the new foliage on the other stem look like?

Normal.

In that case, you might want to risk waiting to see whether new growth going forward is normal or continues to be distorted. With viruses, the difference is really stark. Everything after infection will be distorted/small/sickly, while older foliage will remain looking the same (not including normal signs of aging or fungal disease that may happen).

It was warm and cloudy today, and the new growth looks normal now.

FYI, although I don't think your plants have the virus, there are a number of tomato breeds from Idaho that are supposed to resist the curly top virus (e.g. the Payette tomato, which I've grown a couple times: it's a dwarf with rugose foliage; I haven't tried the others). I don't believe I've ever had tomatoes affected by the virus, though.

herbicide damage