Experts and BHG readers answer.
Black patches on tomato and pepper plants
Thanks for writing. Without being able to see your plants, I'm afraid I can't diagnose the problems for sure. There are several diseases that can affect tomato and pepper stems (the plants are closely related). Your best bet is to bring a sample to the folks at your local cooperative extension office or university; they should be able to help identify it after examining it in person.
There are some fungicides that may stop the disease from spreading much farther --- but it's really helpful to know what you're dealing with before spraying.
---Justin, Senior Garden Editor, BHG.com "