Two problems are happening in tomatoes right now. One is leaf spot diseases whether early blight or Septoria (both are caused by fungi). Things to incorporate in your routine are to stake or use tomato cages to keep the plants off the ground improving air circulation. Keep the plants dry by watering at the base of the plants or water in the morning allowing plants to quickly dry off. Pinch and discard infected leaves. I have found covering the soil with mulch whether plastic or straw helps. Using a fungicide like Daconil on a routine to prevent the spore from infecting healthy leaves.
The other pest on tomatoes is the tomato hornworm. The large 3 to 4-inch worm is quite hungry and will quickly eat the ends of the plant. They emerge into the large Sphinx moth which does not harm anything. I found handpicking in early mornings (they eat and are visible during cooler temperatures) is the best control. You can use insecticide; however, they will still eat before dying. Some have found planting dill or marigolds with the tomatoes will help.
