I'm getting conflicting diagnoses. Is it the start of blight? Mosaic virus ? Bacterial infection ? Or a deficiency in something ...magnesium ?
This was a recent discussion on this subject-my feeling is you will find the answer there
If not italiophile will be along at some time -he is the tomato guru
Are these actual yellow spots, or a more general yellowing between the leaf veins?
They are seperate fairly round , pea sized spots. I am removing quite a lot of the leaves as the light levels are so low and to improve air circulation.... keeping greenhouse door open plus windows.... should I close at night ?
joanna, can you post a photo? It's always easier if we can see the probem. Doesn't guarantee a diagnosis, but it helps. Are the spots actually yellow? Or a pale brown/fawn, as in necrotic (dead) leaf tissue?
And when you say the light levels are low, how much sunlight are the plants getting?
With the summer we are having sun would be a real bonus ! The spots are more fawn coloured.... would love to post a pic... not possible at the moment sadly. The outdoor plants are fine , so far.They have also started fruiting whereas the greenhouse ones are still very green.
Do the spots look like this?
Not as extreme ...those are dead patches and maybe mine will become like that but in size and shape they are similar. I am really grateful for your input Italophile ..thanks.
Yes, that's necrosis, dead tissue. It can be nothing to worry about in terms of disease. Fertiliser burn can cause it, and sunburn (though probably not in your case!)
Are the spots on the top or underside of the leaves? And where are the leaves on the plant? And, last question, is there any sign of a darker spot forming in the middle of the current spot?
The spots are yellowish on the top of the leaves and brown on the undersides and leaves are affected from top to bottom of the plants. The variety worst affected is Brandywine Pink. No sign of darker spots in the patches.
Brandywine Pink? It is a Potato Leaf? With the almost smooth, slightly scalloped edges? As distinct from the traditional saw-tooth edge of a tomato leaf? Glorious tomato. Possibly the best I've ever tasted. Only Marianna's Peace comes close, I think.
It's so hard to know without actually seeing anything. Did you notice whether the problem developed from top to bottom or vice versa? The brown underneath hints that it might have developed on the underside. Septoria Leaf Spot does that and it, along with Early Blight, are the most common fungal problems in the home garden. They both tend to start from the bottom of the plant - the older leaves - up. EB is more apparent on the top of the leaf and pretty quickly develops a "halo" around the spot.
You might not want to, but I'd be inclined to leave one leaf in situ and watch it. If it's SLP, you'll see little pin-head type mini-bumps develop inside the brown patch. If it happens to be SLP it won't terminally damage the plant if you contain it. None of the fungal problems do massive instant damage - except Late Blight, which will kill a plant in weeks - and the onset of cold weather usually terminates things before the fungal problem does.
Sorry I can't be more specific. Without an image, it's sort of guess work.
I overlooked your earlier query about doors and windows. Air circulation is an absolute priority in greenhouses. A closed environment can be an incubator for all sorts of nasties.