These leaf spots will quickly enlarge and a white mold will appear at the margins of the affected area on the lower surface of leaves.
14+ Purple Spots On Tomato Leaves. Purple under leaves of tomatoes is a trait of phosphorus deficiency. The plants themselves (don't know if this is a coincidence) also seem to turn out stockier, shorter, and thicker in the end, and curl a bit.
Potassium Deficiency Plants Wikipedia from upload.wikimedia.org
Perhaps not enough magnesium to uptake the phosphorus? Leaves with brown edges may be caused by purple leaves are caused by expression of anthocyanin due to light exposure. Tiny irregular brown spots, streaks, and ring spots usually on the yellowing and purpling develops on mature plant leaves, while calico symptoms appear on young.
Problems on tomato leaves can mean the onset of a disease, an attack from a tomato pest, a nutrient deficiency, or conditions that can lead to trouble.
It is a leaf spot disease that is first evident on the oldest leaves of the plants. On tomato leaves, the disease first appears as small, brown spots with light brown centers and darker brown margins (figure 6). However, they still have it and i am not sure what to do. Read this article to get tips for treating septoria leaf spot.
