I don't think that copper is an effective soil fumigant. Copper has antibacterial and antifungal properties, but the copper ions have to touch the organisms to kill them. That's what happens on foliage, when the organisms land on treated plants. In order to sterilize the soil to depth, you'd have to use an enormous amount of copper.

That being said, there used to be great soil fumigants that would kill (by vapor action) EVERYTHING in the soil - e.g. Vapam. Those aren't allowed for residential use anymore.

Vapam, Sounds yummy!

Yeah, like Napalm is yummy. ;-)

Seriously once you understand that (1) the fungi that cause septoria and all the so-called "blights" are airborne spores and exist all around us and (2) that direct contact with the spores is required for them to be killed, and (3) they only proliferate on out tomato plants under certain atmospheric conditions of temp, humidity, and lack of air circulation then soil treatments are generally unproductive and waste of money.

Now if your wanted to hire a crop duster and have him Vapam all the acres and foliage and soil for miles around you might see some benefit. But as much benefit comes from working on all the good garden hygiene practices of mucho spacing of plants, clearing away foliage around the garden, weed control, pruning as needed, mulching, increasing sun exposure as much as possible, cross-wind planting, etc. But they all require more work. ;-)

Dave

I'll have to talk to my neighbor, coz his plants are way tighter than mine.

In fact, with proper mulching, you can seal off your plants from the soil underneath them pretty effectively. What that won't do is seal off your plants from all the soil around them. That's why mulching is of some help in avoiding fungal infections, but it is hardly a way to wholly prevent them.

Ah, Vapam. Those were the days. But metam-sodium (Vapam) causes birth defects and fetal death, and is a known mutagen. It's a carcinogen, and a neurotoxin. Oh yeah. It's not good for bacteria or fungi either. In fact, it is the third most commonly used agricultural pesticide in the United States. Commercially, I believe it is the most commonly used one for tomatoes.