Good for you for reaching out here, Ed! 

It can make a world of difference if you catch tomato diseases early.

It sounds like you are experienced in transplanting and determining when to water.  Well done!

This year, we've had some extremely hot & dry spells and THEN strong thunder storms.  So providing even watering and avoiding backsplash on the lower leaves of tomato plants has been challenging for us all.

Because you caught this early:  I can't be sure which fungal disease you are battling here....but this fact sheet from the University of Minnesota's Extension (they have similar climate zones) may help:

https://extension.umn.edu/plant-diseases/tomato-leaf-spot-diseases

The advice stands for all possible fungal diseases:

• Cut off the infected leaves
• Do your best to water your tomatoes only at their base (not on any of the leaves)
• Mulch (as always:  leave a few inches away from the stems)
• Do your best to provide air circulation for your tomato plants

Finally:  this is often really hard for those of us with home gardens with limited sunny spaces... but if you can find another spot in your gardening kingdom where tomatoes might receive enough sunlight to grow in the future:  DO rotate your "crop" here.  Best to avoid the current location for at least two years since so many of these diseases overwinter.

I hope this helps....and that you are gifted with a hefty tomato crop this year.....and a new space to plant tomatoes next year,

- Robilee Smith 

Hi again Ed!

I ran your photos by Ann Hazelrigg, the director of our UVM Extension Plant Diagnostic clinic.

The good news is that Ann says you are not battling a fungal disease (my apologies for the misdiagnosis on my part!). 

Ann identified two problems that she sees in your photographs:

1) Flea beetles:  these should slow down now.  Here's a good fact sheet from the University of Minnesota's extension service on flea beetles: https://extension.umn.edu/yard-and-garden-insects/flea-beetles

Note that flea beetles overwinter....so cleaning up debris and, if possible, crop rotation can help. For tomatoes:  planting a bit later than usual can also be a good strategy.

2) Magnesium deficiency (the chlorosis in the leaves is the key clue here).  Ann notes that most commercial growers just prune these off;  but if you see that the chlorosis continues on new leaves: then you can take action by applying a diluted spray of epsom salts.  Here's an excellent article that Ann recommended explaining how to do this:  https://www.growveg.com/guides/fix-yellow-leaves-on-tomato-plants-using-epsom-salts/

Note that you may have sufficient magnesium in your soil;  but if too much high-phosphate fertilizer is applied, plants can't take up the magnesium.  So check your tomato fertilizer -- you may need to lighten up here.

Glad that your tomatoes are facing early blight or another fungal disease.  These two problems are surmountable.  

Hoping you enjoy a good harvest,

- Robilee Smith

Ed:  correction of error at the very end of my note:  I'm glad that your tomatoes are NOT facing early blight or another fungal disease!  Flea beetles and magnesium deficiency are much easier to remedy.