What can prevent early blight in tomato plants?
Thank heavens you at least are enjoying a good harvest! The problem is usually Phytophthora, which is a fungus that spreads rapidly in wet, humid conditions, and usually when it is cool. Are you setting your plants out when it is cool? There are reports that this organism can get started when the temperature is around 50 degrees for two days. I wonder if you could try planting a little later. Other than planting a little later, some fungicides might help, but I really don’t recommend spraying plants that are eventually going to produce food, unless necessary.