Need help identifying this disease!

[Sunfreak]

Hi everyone from Germany! My name is Michael. I have poor english language skills. So please be patient. This is the reason why i'm so silent. But i'm reading here very often...

My tomatoes are diseased!

I have no idea what it could be. Affected are the leafs and the stems. The leafs wilt and dry out. The stems are turning into a olive green coloring. It is possibly affected just the rind (cortex) of the stem. The rest of the stem are looking healthy (e.g. pith).

I have never seen this before. What do you all think?