The first plant is an Isis Candy. It suffered some defoliation by squirrels last month, but not too bad. The yellowing seems to be traveling up the plant. No spots, just yellowing.

You can see the interesting progression of yellow up the stem.

and another one:

The second plant is a Brandywine, and it exhibits signs of interveinal chlorosis. This plant was pretty damaged by the squirrels and suffered some significant defoliation, which is when I noticed the first leaf with the yellowing pattern. It does have lots of new, healthy grown, shown below, so it's hard to tell.

There are a few spots on this one...hmmmm- not sure if that means anything.

and healthy growth:

Considering I'm new at this- I don't know how much yellowing, if any, is normal, and I don't think that interveinal chlorosis (assuming I am identifying it correctly) occurs in an otherwise healthy plant.

Any thoughts?

In addition you may have blight. Did you use garden soil or bought soil.

Yellowing is not normal. Spray the leaves with an organic fungicide in early morning, and you will have to do this often. When you water don't wet the leaves And since they are in containers maybe you can rig up some plastic shield above the plants to keep the rain off of them. Blight is carried in the soil and is spread by water splashing from the soil on to the leaves or infected leaves on to other leaves and carrying the spores with it. Remove all infected leaves as well as the bottom ones.

oilpainter- Thanks for answering. The plants are in 5:1:1 mix, not a store bought mix. It's 5 parts pine fines, 1 part peat, 1 part perlite. I have 12 containers with tomatoes in this mix and using the current fertilizer program. 2 plants have the yellowing pattern in the first example, and just the Brandywine in the second example. They are also mulched and carefully watered to avoid soil splash, and I spray regularly with Daconil.

1/3rd dilution twice per month equals 2/3rds strength monthly. You likely should be providing full strength every 2 weeks. You can break this up into more dilute doses or give it all at once on an every other week basis, your choice.

Nevertheless you may have a fungal disease going on as well.

I just fertilized at half strength, and I'll wait two weeks again and fert half strength again. I am going out today to put shade cloth around the containers, as they are black and going to start cooking the plants...our highs have been in the 90's the past few days. June gloom is over!!! :) Fortunately the plants don't get late afternoon sun.

As for the yellowing- I will step up the frequency of the Daconil applications and remove the effected leaves. It might leave the Isis Candy a little sparse, since it doesn't seem to have near as much foliage as the other varieties that I am growing, but I did successfully rid my plants in another garden bed that I have of a fungal disease by spraying the plants and removing diseased leaves. The plants looked pretty pathetic for a few weeks, but they eventually came back.

My, aren't I the Chatty Cathy today...thanks for your help, and happy gardening! :o)

I would suggest bumping up your fertilizing schedule and see if that helps. Also, you might want to consider pruning. Many people say whether you prune the suckers or not doesn't really matter in the long run. I'm doing it this year because I've been having problems getting my plants to grow tall in past years and I think it helps focus the plant's energy on the tomato producing branches. It might help some of your plants to prune off the troubled areas. But I don't know -- I'm experimenting with this too.