Why are my tomato plants showing a discoloration on the lower leaves?
My tomato plants are showing a variegated discoloration especially on lower leaves. Several varieties are affected.
I was concerned about the concentric circle lesions on a couple of leaves (typically a symptom of early blight), so I reached out to our plant pathologist, Dr Alicyn Smart, for her diagnosis. Unfortunately, she confirmed my worry:
“The fungal disease Early Blight, caused by the pathogen Alternaria solani, was identified as the cause of the observed symptoms. This disease typically starts at the base of the plant and then works its way up. It can affect the stem and fruit when the disease is further along. Since there are only a few of the lower leaves with this, I would recommend removing them and throwing them away. Do this when the leaves are dry, so as to not spread the spore around.
Next year when selecting seed, make sure to choose a cultivar/variety that is resistant to this disease. Many times you can manage the disease by just selecting plants that have a higher tolerance to this pathogen.”
The UMaine Cooperative Extension has an excellent resource on the disease here. You can mitigate fungal problems by always providing supplemental (i.e., non-rain) watering directly to the soil and maintaining spacing between the plants to promote air flow through the leaves.
I wish I had more positive news for you, but the good news is you may be able to save these plants and, if not, it’s not too late to replace them.