There is a great thread called " HELP!!! Tomato Problem Solver 2"
If you go to Disease Management in Tomatoes, and then Fungal Leaf and Fruit Spots or Blights.

The First Picture is of Septoria Leaf Spot (Septoria Blight)
it looks like whats on your leaf in the picture.

Linked forum in case it slides out of sight

I am just learning about the diseases myself, I can't confirm, just those pictures looked very similar to each other )

Good Luck

Joyce

Here is a link that might be useful: Tomato Problem Solver 2

You are right, the pictures are very close and Septoria Leaf Spot seems to be a common problem in New England. (And we just had a week of rain.)

The Sungold plant (worst infected) was the only seedling I purchased. But the Sugar Lump plants are in two separate beds far from each other and far from the Sungold. I am wondering why would only those plants be infected? Or be infected first?

I'm not sure, I have Early Blight which seems to be very close in behavior (Fungus, airborn, spreads during the same conditions as one another)

Most recomend Daconil/Ortho Garden Disease Control, I told my husband when i sent him after it make sure you can use it on produce. and He came back with the right stuff ))

It seems to be working in slowing the fungus down.

All of my plants are affected to one degree or the other now, however the ones I started and sent to other homes are doing very well, and they are disease free with no extra effort.
And I didn't have any problems last year at all with my plants they were very healthy.

Good luck,
Joyce

Upon closer inspection it seems that some of the brown on many plants looks more like a pest eating away at the underside. Could it be a slug or something else? Do they do this much damage?

There are several good links to pest problems also, The link below is to a Vegetable Insect ID. They say slugs tend to skeltonize or shred the leaves.

Take a close look in your garden and take note of the bugs ya see there, not all are bad though.

Joyce

Here is a link that might be useful: Vegetable Insect Identification

Definitely have seen lots of the red-headed flea beetle around in the garden! And there lots of very small green flies. (??) Haven't been able to identify what they are. They rest right on the leaves of my tomatoes and tomatillos and my guess is they aren't up to a lot of good.

I grow with organic methods, so I'm unsure what to...

Perhaps a brief water shortage? the soil went dry? Or a hot windy day?

The odd thing is, I have that exact same stuff on my Sungold plant! And on none of the other 27 varieties I am growing (I am not growing Sugar Lump).

I am pretty minimalistic in terms of interventions (I do handpick insects I know to be harmful, like &*^%$ stink bugs), so I have done nothing about it. The plants are over my head and loaded with fruit (I ate my first ripe ones today, delicious!!!), so I guess it's not immediately fatal, whatever it is.

Is your new foliage growing in OK?
Shaila

That is interesting!

I signicantly pruned the Sugar Lump, and while it looks rather skinny and sparse now, it did bear a few fruit over the weekend.

But the Sungolds were SO brown looking (nearly the plant, both Sungolds in separate beds), that I pulled them, as I didn't want to spread anything if indeed it was bacterial.

Perhaps I didn't need to pull them, but I do still have 55 plants, including lots and lots of cherry and grape tomatoes. Even so, I will miss enjoying Sungolds this year!