This is our first attempt at tomatoes. Black fungus is growing all over it. I looked it up and apparently the fungus is actually growing on honeydew, and the honeydew comes from aphids and whiteflies. So I treated it with All Seasons Horticultural and Dormant Concentrated Spray Oil, but when I checked it a couple days later, it looked even worse.

Perhaps it isn't in the best environment. Our yard doesn't have grass, it's a collection of green weeds, which if I remember correctly, harbor those little bugs.

My other suspicion is that maybe it's the spot where the plant is. It didn't look like this until I moved the container over a spot where the old septic tank used to be. We had it decommissioned two years ago. It had been disconnected when sewer lines were installed, but abandoned. The soil above it won't let anything grow in that spot, (you can see the dead grass in a couple of the pics,) so I'm wondering if that has something to do with it, even though the tomato plant is in a container. Other plants around it that are not sitting on that spot are doing ok.

Work 3 months, spend one hundred dollars harvest 3 dollars worth of tomatoes. Or go to the farmers market and buy 2lbs for 3 dollars. they do taste just as good as the home grown toms no matter what we keep telling ourselves.

Brinybay, It appears that the plants are being grown in containers. We grow our
tomatoes over our drainfield and have never had an issue with them. Ours get
well over 5 foot tall! Tomatoes in containers can be tricky so how about next
year putting them directly into the ground? If the tank is decommissioned than
it should be fine to grow in this area. Tomatoes love sweet soil not acidy so that
might be an issue. As for the fungus, a lot of stores have no clue as to the proper
care of plants so you may have brought it in that way. Better luck next year.

Brinybay,

Several things are visible in those pix, but first: as Karma said, the old septic system is unlikely to be connected to anything.

Your plants are not getting enough sunlight. The long spaces between leaf nodes (called etiolation) are a clear indication of that. Therefore they were weak, therefore susceptible to disease and insect attack. (What you're calling black fungus is actually called sooty mold, which forms on honeydew, btw). If the plants were exposed to sunlight after you sprayed them, they could have become burned. Also and especially in your area, inadequate sun exposure encourages development of fungal and moisture-borne bacterial disease. Move them to maximum exposure—7 or more hours a day. Water in the morning, don't let water or soil splash onto the leaves.

I think I see blossom end rot on a couple of the fruits. That is a calcium deficiency that is usually caused by uneven watering. Your soil looks dry. It should remain evenly moist (not wet). Tomatoes in containers also need regular, consistent fertilizing. Managing both water and fertilizer are trickier growing in containers than in the ground. The containers should be 5 gallons MINIMUM.

Beyond those controllable (by you) issues, your plants have some disease. Honestly, tomatoes are susceptible to so many disorders, I'm never sure what they have. (Other people do, hopefully they'll weigh in). Some are really obviously identifiable, some aren't, and sometimes the plants suffer more than one, so the symptoms are confusing. Further, as with some of the wilts, the leaves will die but the fruit will hang on and remain edible. Some are controllable, few are fully curable, many are terminal. Here are some sites for identifying disorders.

http://vegetablemdonline.ppath...

https://hgic.clemson.edu/facts...

https://extension.colostate.ed...

In spite of all the hype and gazillion websites glorifying guaranteed gratification of growing tomatoes, it's not for the faint of heart or easily discouraged. But doable with trial and error! Good luck!