It's likely that your plants have Pythium infection (black leg). You need to improve drainage, especially with a lot of wet weather and heat.

Xeric and high altitude sages, such as those from the Andes, are especially vulnerable.

Here is a link that might be useful: Geranium-Phythium Blackleg

Shoot, it's serious. Thanks Rich, I really appreciate your expertise. Best, River

I am so glad to see this post because I have the same problem with my May Night. I knew they weren't doing well by the leaf drop and poor blooming but had never checked for blackened stems. I checked and they were black.

So I pulled them out, fearing the disease would spread to the dahlias they surrounded. Now I see white moldy spores on the soil in the bed and wonder what to do about that? Do I treat the soil with something?

The article didn't mention whether this disease could spread to adjoining plants like Dahlias, does anyone know?

And how did I get this in the first place...the bed was not overwatered, the salvias were in their third year of bloom and kind of rangey.

Thanks so much for posting this.

Hollie

Moldy spores (sclerotia) might be an indication of Southern blight, which is mostly indiscriminate. I've found a pretty thorough article on its description, symptomatology, and control.

Here is a link that might be useful: Southern blight

I know this is a old post, but i have searched the entire web and its truly the closest I have found to my current situation *fingers crossed* I have been caring for 2 sage plants in containers that I purchased a few weeks ago, and the stems are also turning black (although not soft/mushy to the touch like rot, they feel quite hard) Could it possibly also be ‘black leg‘ disease?

Thank you