Black spots on tomato stems - diagnosis?
 

Hi Folks, asking for a friend in Barcelona, Spain. I've had a look through the stickys, but can't really find anything appropriate.
His tomatoes have these large black necrotic areas on the stems. He grows in a community garden, and many of the plots are suffering. The locals are confused, haven't really seen it before.
It doesn't seem the leaves are affected (yet). the stems have discolouration in cross section. Hoping someone can help an Aussie asking from Oz for an Aussie to help the Catalans in Barcelona!

Hello, Alternaria If close to the soil or stem rot are my thoughts. Are you sure there is no disease on the foliage? Late blight can also look like this on stems but almost certainly There stocks be foliage disease as well.

I've looked at Cornell University site for Tomato Diseases and it is most likely Alternaria Stem Canker, which pretty much is the death knell of the plant.



If it were Late Mold/Mould, the black lesions should have a noticeable white margin around them, which the photos don't show.

As above.


Cornell University Reference here - [URL]http://vegetablemdonline.ppath.cornell.edu/DiagnosticKeys/TomLeaf/TomLeafKey.html[/URL]

Late Blight causes spots like that but you would also see irregular, sunken brown spots on the leaves. It is incurable.

Possibly Alternaria stem canker. I searched "black necrotic spots on tomato stems" and found this:

[url]https://www.gardeningknowhow.com/edible/vegetables/tomato/black-stems-on-tomatoes.htm[/url]

Thanks for the link, GoDawgs. I've had the black spots on tomato stems, brought one plant to the Extension Agency where they suggested removing the plant altogether. I removed 3, and didn't plant tomatoes or peppers in that area for 3 years.

thanks for all the info and links. will investigate and pass on.
T

Here is a good link with description, no pics unfortunately. [url]https://www.seminis.de/informationen/krankheitsleitfaden/tomatoes/alternaria-stem-canker/[/url]

It does seem to fit in this case, haven't seen it before.