I grow tomatoes yearly and have had a problem every year with that. Try to clip off the impacted leaves, also check the soil with your finger and make sure you are not overwatering. The soil whould be slightly dry, several inches down befopre watering again. When you do water, water at the base of the plant and not all over the leaves...unless you a foiliar feed such as Garrett juice or something similar. I would also put a couple of handfuls or corn meal under each plant and work it into the soil.

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