It looks like a deficiency. I believe nitrogen but I could be wrong. Someone smarter will likely be able to tell you for sure. It's not blight though. Blight is kinda like if a leaf could have a scab on it.

Just lower leaves affected? Hard to see in the sungold foliage but the BW leaf just looks like the plant might need some nitrogen, I agree. You might try giving some soluble fertilizer.

Yes you always remove any damaged or affected leaves from the plants - no reason to leave them on - and dispose of them away from the garden.

The first photos "might" be some Early Blight but would need a much closer pic of the spots to see. It won't blow up enough to see them clearly.

Most of the yellowing on the older leaves is from over-watering and secondarily, insufficient nutrients IMO. Sq Foot Gardens normally don't feed plants effectively and require supplements so what and how much have you been feeding them? Details please. Have you had lots of extra rain? If so that would explain it. If not, cut back on your water.

Fungicide is almost always beneficial in the early spring given the weather. Whether you want to use copper or one of the more effective synthetics is your choice. Just be sure to follow label directions and keep in mind they are all just controls, not cures.

Dave

There has been some rain, but not too much. But maybe that? I have not been feeding separately. I have heard of fish fertilizer? I have to do some research. If I want to stay organic, what kind of fertilizer should I feed to fix the nitrogen matter, and generally going forward, and how often? Bed has mix of few different compost mixed in including composed chicken and cow manure, worm casting, lobster compost, hummus compost, etc. I have some earthworm casting fertilizer handy but can get other stuff too.

I will post more pictures below! thank you!

As far as disease, I know nothing so I am going to defer to other experts.

But on the fertilizer issue - assuming that is what is needed - I like fish fertilizer but prefer Neptune's Harvest to Alaska (which is what's available in most stores around here). The regular formula of Alaska Fish Fertilizer is 5-1-1, which is too high in nitrogen for my tastes. There is an Alaska Bloom formula which is more suitable for tomatoes, although I do not believe it is entirely organic. But, it may be the easiest option for you to find. Be prepared, it is really smelly.

Neptune's Harvest is harder to find but some hydroponics stores in my area carry it now. But, we have an unusual concentration of hydroponics stores in my state :) It is entirely organic. It is a better nutrient ratio and more available to the plants immediately than the Alaska brand. It smells of fish as well, but significantly less.

I also love Texas Tomato Food but I did have to order it online. Delivery was very fast though. It is not *quite* organic, but almost. That is okay for me. It is a new product for me but I'm very impressed so far and it does not smell nearly as much as fish fertilizer, which always attracts a lot of flies when I apply it, and leaves a smell on my hands (even the Neptune's.)

Wormgirl - I found everything you mentioned on Amazon prime! This working mom with two littles cannot live without amazon prime :) Seems like Neptune's is 2-3-1, and is $17.05 for 36oz. Not sure if that is a reasonable price.

Now just waiting on other responses to see if I need to order copper spray as well...

Neptune is a bit on the expensive side. Ive used Dr. earth in the past with good results too, but this is expensive as well. You can always use a synthetic. Something like MG is only around 5 bucks a box and will give it the shot it needs. You can use the bloom booster blend which is 10-54-10 or something crazy like that.

It's true, it's a bit expensive but worth it IMO. The price is reasonable that you saw. I usually order a gallon but go for the quart and see if you like it!

I have also used Dr. Earth and it was way up there on the smell scale - my neighbor said, "It smells like when I used to express my dog's anal glands." And this was just the general smell in the area, not whiffing it out of the bottle. It also caused a plague of flies in my garden (I have a south facing wall which attracts them anyway). So I have bad memories of the stuff :)

If you haven't been feeding the plants then that is the primary issue. Compost is only a source of nutrients IF there is an active soil food web, an active mircoherd, in the bed. That doesn't exist in most sq foot beds until they are several years old and some dirt has been incorporated. Even then it is only a low dose of nutrients.

There are literally hundreds of well balanced liquid organic fertilizers available with a wide range of costs so yeah some research is needed. Until then make up some compost tea with all the stuff you have on hand and feed them with it. A shovelfull of quality mixed composts in a 5 gallon bucket filled with water and let sit in the sun for a couple of days until it turns dark brown. Makes you 5 gallons of good fertilizer cheap. Then dilute it to the color of weak iced tea and give each plant a good root drench with it each week. Google 'hot to make compost tea" for more details.

As for the copper, that is your choice. The last set of pics does look like EB to me. When it comes to fungicides copper is better than nothing. Sulfur is better IMO and Serenade is better than both and still organic.

Dave

Uhoh. That plant seems to be declining rapidly. It makes me wonder if it is, indeed, a disease. You will be happy with the Neptunes and at the least it will help your other plants.

I'd snip everything yellow, leaves and branches, then hit it with Serenade asap. Reapply after one week or after the next rainstorm, whichever comes first. Regular preventative spraying is your new friend, especially in this rainy/cool weather many of us are experiencing. It may be some combo of lack of nutrients or lack of nutrient uptake, too much moisture, cool evening temps, weak plant genetics. If the plant declines even further then consider yanking and replacing it.

Good luck either way.

Steve

Yes, we try to go for the undersides too, and at the same time we do preventative sprays with the healthy plants. Maybe every week or two, but especially after most rainfalls since mold/bacteria splashes up from the mud. Crossing my fingers for you...

Steve

Look into wilts, fusarium and verticillium

Judging from the last picture (posted 5 hours ago) I see the yellowing starts from the lower leaves. In my view, plant is just aborting those older leave to support the younger ones . I would think lack of nutrients associated with too much moisture ( due to rain, bad drainage/soil).
But There is a possibility of disease as evidenced in the earlier photos , showing lesions.

I would take Steve's advice : Trim off all the yellowing leaves, as the is no chance for them to revive. In the meantime the offer and open door for disease.
Next step is to fungicide the plants
Third, feed them !

Yeah I've got to agree, that can't be simple deficiency. Waterlogged is a good guess.

I used Neptune's Harvest and Big Bloom (FoxFarm) and I was happy with both products.

I also used copper and I was VERY
happy.

I think fabric mulch is
the best to control the water intake from the rain.

Yes, you need dripping irrigation, which controls accurately tomatoes' water needs.

Straw mulch allows MUCH MORE water intake than fabric mulch - which most of the times is not good.

Bummer on fusarium wilt. It is a tough one. I lost large plant to it last year.