Lee,

I can't see the interior structure of the spots that clearly but it's either Septoria Leaf Spot, which I'm leaning towards, or Early BLight ( A.solani) and both are common fungal foliage pathogens and would be treated the same way.

The fact that you see it only on the bottom leaves means the infections are from splashback reinfection from previously contaminated soil since all NEW infections are airborne.

Carolyn

The fact that you see it only on the bottom leaves means the infections are from splashback reinfection from previously contaminated soil since all NEW infections are airborne.

Probably so, but it is frustrating that this happened even though I put down a straw mulch. I have never mulched before, so I wanted to try it this year to see if it would help prevent splashback problems!

What are the distinct characteristics that distinguish Septoria Leaf Spot from Early Blight?

Lee

Septoria has little black dots within the leafspot which are the fruiting spores of the fungus.

With early blight you may find concentric circles within the leafspot.

http://www.ento.okstate.edu/ddd/diseases/earlyblight.htm>

Here is a link that might be useful: Septoria

Oh, so if it is Septoria, I should remove the infected leaves ASAP so no more fungal spores come into being?

Lee

If you read the Early Blight link it also says this: "Thousands of spores are produced in spots of infected leaves that are capable of causing more infections. " so spores are not just a factor with septoria.

Maybe I should invent a Carolina Quarantine Cage to help keep the spores away from other plants once disease hits!

Lee