Both downy mildew and powdery mildew will produce black lesions on grape stems.

I'd venture anthracnose. I have it on my grapes this year, for the first time ever. Showing any symptoms on the leaves?

in the other forum.. i started the discussion with wondering how you successfully grow a very aggressive vine.. in what looks like a rather small pot ... in what looks like a high peat media ...

one often looks to the plants CULTURE... before suggesting remedies ...

in other words.. if you are growing a severely stressed plant... fixing some problems.. may not decrease the stress ...

ken

thanks calliope! that looks exactly like whats going on. only one of the base leaves has shown any symptoms, the rest of the plant looks great.

I grow all my edibles totally organic, so I'm immaculate with keeping my grapes culturally 'clean'. It happened anyway this year, and I'm not too surprised. We've been living in a terrarium for two months. High humidities, showers nearly every day, heat. I'm going to have to really prune out well this year (had them pruned just how I wanted them and hate that) and likely do a spray at the appropriate times until it gets under control.