Early Blight of Tomatoes

For the first time in twenty years my tomatoes had early blight. I used the recommended chemicals, but to no avail. How do I prevent this problem next season?

Plant selection and sanitation will help reduce the risk of this disease. Remove and destroy infested plants when you clean up the garden this and every fall. Rotate plantings to reduce the risk of diseases and insects infesting all your plants. Remove weeds that can harbor this disease and mulch the soil. Plant resistant varieties such as Floramerica, Mountain Fresh, Mountain Supreme and Plum Dandy.