I dont want to guess wrong ,but here is a good way to judge for yourself

Here is a link that might be useful: Disease Diagnostics

Simplest diagnostic:

if the spots stay small and don't get much bigger over time that's septoria

if the individual spots get larger and on the inside make rings or a target-like pattern. That's early blight.

Bacterial issues take a little more investigation about the pattern, weather conditions, field pattern and other symptoms

Either way the treatment is the same.

Dave

And the treatment is?

try this link

Here is a link that might be useful: Early Blight

Thanks for the link and the information. Such a wealth of knowledge here.

Would it be possible for my cages to be spreading it to? I mean overwintering on it?

And the treatment is?

The same as what is discussed in all the other posts currently running here about fungus diseases on tomato plants. Strip off all the affected leaves and begin a regular fungicide spraying program in the hopes of slowing the disease until harvest.

Dave

From the LINK I provided You to read:

Survival and Dispersal
The fungus spends the winter in infected plant debris in or on the soil where it can survive at least one and perhaps several years. It can also be seed borne. New spores are produced the following season. The spores are transported by water, wind, insects, other animals including man, and machinery. Once the initial infections have occurred, they become the most important source of new spore production and are responsible for rapid disease spread.