Went away for 3 days and now my tomato plants are yellowing!

My tomato plants are in a small plot, which is a turned-up old flower bed that's been covered in black tarp and landscaping stones for several years. When I transplanted the tomatoes about 2 weeks ago, it was a hot day followed by several days of rain and about a week of cooler weather.

They were a little droopy, but I thought they might just have some transplant shock. Well, now they're still droopy during the day and all the leaves on the bottom half of all the plants are yellowing in a spotty vascular pattern, with the veins still bright green until the yellowed areas turn brown and the whole leaf starts to die.

I've just discovered this, so it's happened in just the past three days. I'm thinking it could be Septoria, and hoping it's not the early signs of wilt. I don't see any obvious signs of bugs or the concentric circles of blight. Can anyone help me say definitively what's going on and how I can fix it on a budget? Thank you so much in advance for your time. This little garden means a lot to me, and my tomatoes are the only plants that aren't thriving.

Tomato Dirt responds
We're so sorry to hear about your tomato problem!

The disease looks and sounds like verticillium wilt. Characteristics of "vert" include:

• leaves turn yellow, then brown, then drop
  
• leaves develop veins
  
• plant wilts during the day
  
• interior stem (when split) shows discolored streaks
  

Verticillium wilt thrives in cool temperatures, which fits the week of cooler weather you had just after planting.

As of right now, there's no treatment. Plants may survive but will produce inferior fruit. You can slow the disease with fertilizers high in nitrogen and potassium.

If you're not too far into your growing season, you may choose to destroy plants and replant new seedlings, perhaps choosing varieties that are resistant to vert. Late the season, many garden centers have their tomato plants on sale, so if you don't have many plants in your garden it may be economical to replace them.

The fungus lives in the soil. The tarp will trap it in. Next year, you may want to rotate where you plant tomatoes to avoid the wilt.

You can learn more about verticillium wilt here.

Good luck and happy gardening!

Your friends at Tomato Dirt.