Sorry to say that's what it appears to be. I've always thought it's caused by contaminates in the soil. That's why sterilized soil is often recommended.

You could sprinkle some cinnamon or sulfur on the soil to deter it further and to, hopefully, save the others.

Gail

Thank you Gail - especially for the cinnamon part. After you informed about it, I came to know that along with it, camomile tea (high in sulfur) and garlic tea are also good options for treating (preventing) this disease.

I had a properly sterilized potting mix. However, I was thinking if damping off is possible in a well established seedling with 2 or 3 sets of true leaves? Does it affect bigger seedlings / plants also?

That is a MOST interesting picture! I haven't had it happen with little seedlings, but when I planted larger plants in my garden, two years ago, some of them looked like that. It almost looked as if something had nibbled away the outer part of the stem all the way around just at the soil line. The plants didn't die immediately, but wilted during the day and revived overnight. Suspecting something nasty, I pulled them up and discovered that the roots looked ok. I sliced the stems longitudinally and found some brown woody "lines". I tried growing the good top part of a plant, and it rooted well in water, but was never quite right. When I did a necropsy, the brown woody stuff showed up again. I suspect something in my soil in certain areas.

Linda

"Damping Off" normally happens with seedlings. I'm thinking Linda had another affliction on her plants. Linda, you could have indeed had something nibble on your plant opening a wound to allow bugs, virus or bacteria to enter.

In the end, anything can go wrong, but generally everything goes right. Sometimes they just need a little help.

Gail

There are three genera and species of fungi that can cause damping off, which is shown in the picture and without one of them being in the grow medium no damping off can occur.

I have never used sterile seed starting mix, no need to if you use a good one. In past times those that have Canadian Spaghnum moss have been a problem. And never but never use potting soil or real dirt, only artificial seed starting mix.

And not just seedlings can be affected, but plants up to 5 inches tall, which look fine until then. There's a great pictures in my tomato pathology book showing that.

Cinnamon does not work to prevent fungal growth although it's suggested by many. Same for sulfur.

Linda, what you describe on mature plants could be one of several diseases.

Carolyn