That looks like fusarium or verticillium wilt, very common fungal diseases of tomatoes. Try spraying prophylactically with chlorothalonil this year.

I would guess Fusarium by the look of the photos, it doesn't quite match Verticillium wilt (I'm not seeing the characteristic v-shaped lesions on the leaves).

Also, I wouldn't bother spraying chlorothalonil since it is not effective in the treatment of Fusarium or other systemic fungal diseases. Fusarium is a soil-borne fungus which infects the roots and chlorothalonil only works to prevent (not treat) foliage-type diseases.

chlorothalonil only works to prevent (not treat) foliage-type diseases.

Correct, but those photos were from last year. The OP was asking what to do this year. The OP lives in MO, pretty sure there are no tomatoes growing there now.

For this year, spray prophylactically with chlorothalonil.

Ok, so just to clear things up...

Fusarium is s not a foliage disease.
Chlorothalonil only prevents foliage diseases.

Since Fusarium is not a foliage disease, using something that only prevents foliage diseases will be of no use.

Ok. How can you tell fusarium from early blight? They look similar to me.

Noticed that Gardens Alive is selling a root/soil drench product this year for those with a history of F. wilt in their soil. I have no personal experience with it but it might be worth a try. Its name is Root Guardian Biofungicide and is a microbe, Trichoderma harzianum strain so organic approved.

I find it curious the only that one plant seems to be affected in your photos so perhaps it was seed borne. Or did they go down later?

F.wilt vs. E. Blight? Very different appearance in the leaves and in the rate of plant decline plus F.wilt can be diagnosed from the stem lesions and core color. As already mentioned F. wilt is systemic while E. Blight is foliage topical only.

Dave

"Ok. How can you tell fusarium from early blight? They look similar to me."

They are very different and I have personal experience with both.

Here is Early Blight:

Here is Fusarium:

Early Blight only affects leaves and it has characteristic dark concentric circles surrounded by a yellow halo.

Fusarium will cause the leaves to wilt and become completely yellow and die eventually. If you cut open the stem of a plant infected with Fusarium, the center will be brown and dying. Basically the stems will look like the title of this post "Green on the outside. Brown in the inside."

I've had the same experience for a number of years. I've tried neem oil, daconil, copper dust and VF tolerant varieties with little or no improvement. This year we added 600 sq. ft. of new raised beds on a different piece of the property with 7 cubic yards of imported top soil & compost. We noticed Quite a few white grubs while turning over the turf and breaking up the sub soil so we will be trying Hb & Sf nematodes along with a product called MycoGrow. It is a root drench containing endo- and ectomycorrhizal fungi, as well as benificial bacteria, trichoderma, humic and fulvic acids, vitamins, and North Atlantic kelp. One of it's fungi is T. harzianum. Our projected putting out date is april 14 if the weather forcast doesn't take a change for the worse. I will try to post results throughout the season. If this stuff doesn't work I'll be going hydroponic in 2013. I'm sick of it.
Good Luck,
~Ken~

First of all, thank you all so much for taking the time to consider my problem!!!

Second, follow up: This year I
1- mulched
2- have been rather meticulous about keeping the bottom of the plants trimmed
3- redirected the sprinklers not to hit the plants.

That's all I've done...so far so good, but it is still early in the season. Thank you again!!

All good things to do, springerrr.