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First time tomato grower. Got these seedlings from another local gardener. When I first got them I cut off a leaf with two or three dark green spots and sprayed with copper fungicide just in case. I have applied the copper fungicide twice now (once a week as recommended by the instructions). Unfortunately it seems these dark spots are spreading! I’m not sure exactly what’s going on so any advice would be appreciated. Thanks!

This doesn't look like septoria, when my plants get it. It is usually a yellow spot, with a circular dark spot on it, making an eye-like spot.

Yeah, I was going to say they look more like some kind of chemical burn (like oil burn) even before reading pepperhead’s post. Copper fungicide can burn leaves — I had to look up why

Caution with Copper Fungicides and Spray Surfactants in Vegetables and Fruits | Weekly Crop Update

https://sites.udel.edu/weeklycropupdate/?p=5884

Leaves have a protective waxy layer, the cuticle, which prevents entry of copper ions. Copper ions can enter plant cells where cuticles are thin (as with new leaves), through stomates, and through hydathodes on leaf margins. We often see copper injury on new leaves and leaf edges because of this.

Because copper ions are released when copper residues are wetted, we also see more injury when copper is applied to wet leaf surfaces or in slow drying conditions.

Because copper ions can also enter through stomates, anything that would increase the spread of copper over the leaf and increase the entrance of copper ions through stomates and cuticles will increase injury. Research has shown that adding surfactants with copper fungicides greatly increased the injury to foliage.

Depends on where you are, but around here, it feels a bit too early for septoria? You might try something milder if you want to treat young seedlings/plants as preventive. I personally like 1:6 to 8 dilution of milk with non-chlorinated water, plus a bit of whey (yogurt or other cultured dairy ...buttermilk too). This works really well when alternated weekly with actively aerated compost tea (but I can’t always manage to brew one up). I think it was Pepperhead who has recommended potassium bicarbonate solution in the past (in liu of the better known sodium bicarbonate/baking soda), and I have been rotating that in as well. You want to start spraying a week ir two before your rainy season starts.

Thanks everyone for your input. I did some more research and it looks a lot like the pictures I’ve seen of early blight. Does anyone know if this is true? And if so should I just accept the loss and destroy these San Marzanos so they don’t infect the soil in my new raised bed?

Could you post a couple of photos of the entire affected plant? One full shot, and another of the presumably lower leaves that are spotted and 3rd photo of upper to top-most growing leaves (maybe the top three pairs of leaves)

The lowest leaves shouldn’t be touching the ground and the plants should be mulched and pruned so water don’t splash up onto the leaves.

Neither Septoria nor Early Blight are death sentences usually. In typical season, they creep up from the lower leaves and can be controlled, slowed, or outrun (the plants grow faster than they can overwhelm). Generally, infection doesn’t start until wet and humid season (summer rainy season) and by that time, the tomato plants are well established and starting to fruit, so that if nothing else, you can get some harvested before having to call it, lost”, but generally just one at a time, individually.

I would say, here, things don’t start to get really iffy (meaning needing to spray regularly and remove affected leaves, etc.) until corn starts shedding pollen — maybe mid to late June. I usually have to start admitting defeat with some of them around mid July, maybe? But I blame that on my own lackadaisical approach to regular care….

Yes I will attach pictures. My main concern is I just built these garden beds and will be putting other tomato plants in, and I am worried about infecting the other plants. I had removed all of the leaves with spots on them disinfecting the pruners as I went as a precaution. Sadly I forgot to turn off my grow light last night (it doesn’t have a timer) and when I checked on the plants this morning the lower leaves of a formerly unaffected plant seem to have withered and gotten spots. I will attach photos of the original plant with the spots and it’s top leaves which seem more rounded than pointy and the whole plant is smaller than the others. As well as the new plant with its withered bottom leaves and the two plants that still seem to be doing well. Thanks applestar for the advice my plan currently is to wait until it’s been a week since the last fungicide and try using something less harsh than the copper fungicide.

For more context I will also add I live in Colorado zone 5b and the seedlings have been kept inside because it won’t be warm enough for at least two more weeks for them to go out. Since I transplanted to the 1 gallon grow bags I have been watering from the top (not sure how to/if I should bottom water the grow bags?) and I had not mulched them yet. I am going to add some straw to try and stop any splashing of the soil onto the plants during watering.

Here’s the leaves close up