The disease may progress up the plant, especially during wet weather conditions. Mulching can help reduce soil splash onto the plant, which can in turn reduce leaf diseases. Caged or staked tomatoes will have better air circulation, which may reduce disease. Remove infected leaves as soon as they are noticed to help reduce spread. Remove infected plants at the end of the season and also practice a 3-year crop rotation.
Some varieties offer tolerance of early blight.
Fungicides can also provide some protection, but need to be used weekly. Look for fungicides labeled for vegetable crops that contain chlorothalonil, copper, or maneb. Finally, large green tomato hornworms may eat considerable amounts of foliage off tomato plants. These can be picked off by hand. Oftentimes the damage is noticed before the large caterpillar is found.