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I'm growing some organic tomatoes (mostly cherries), and noticed the other day that there were small purple spots forming on the leaves, and they are gradually turning purple and curling inwards. It doesn't look super fungal to me, and it has been humid but not super wet (though it just rained before I noticed the spots). I've been watering with a soaker hose, so trying to keep moisture off of the leaves. Based on my plant-webmd searching, I have thus far considered the following:

  • Fungal/Bacterial spot (but doesn't seem to be a yellow halo around the spots, leaves seem otherwise intact)
  • Phosphate deficiency (but hasn't been cold, had added a bit of manure to the soil when planted a couple weeks ago, and also the veins are still green).
  • Tomato purple leaf disorder (came up in my google searches but seems obscure and only article I can find on it is from Florida, while I am in Southern Ontario..)

Any ideas?

leaves turning purple

starts as spots

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I have something very similar on my tomato leaves. After looking at a lot of photos and reading about many possible issues, Septoria appears to be the most likely diagnosis - especially if like mine, your tomato fruit itself is unblemished as this probably rules out a bacterial spot. I'm not an expert, but I wonder if there is also some synergy among stressors where something about the fungal infection prevent the leaf from properly utlizing magnesium and/or potassium in the vicinity of the spore/colony while the rest of the leaf is ok.

I'm treating by a) removing the damaged leaves and branches, (b) removing the bottom 12 inches of leaves to enhance air circulation and prevent transfer from the soil, c) adding tomatone and neptune's harvest fertilizers to be sure there area ample nutrients and d) applying bacillus subtilus bacteria which is supposed to treat Septoria (I have beutiful ripening fruit and don't want to use fungicide). Too early to see results, but I hope to salvage a 2nd wave of tomatoes in the 2nd half of the summer. Hope this helps.

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