There are different leaf spot diseases in tomatoes such as Septoria leaf spot, bacterial spot, and early blight. At the early stage, it's hard to differentiate between them. Leaf spots should not affect the amount of fruit your plants produce. Most tomato leaf spot diseases overwinter in the soil and then splash on to the lower leaves of the plant. As a result, the first leaf spots can be found on the lowest leaves closest to the ground. Pinch off leaves with leaf spots and bury them in the compost pile. It's better to remove the lower third of the leaves on every plant whether they have leaf spots or not, this improves air circulation. Keep the leaves dry and use drip irrigation or a soaker hose or direct the garden hose at the base of the plant. You can cover the soil below the tomato plants with mulch, stake or trellis tomatoes. Keep pinching off infected leaves to keep leaf spot diseases in check. Tomato plants can tolerate high levels of leaf loss from leaf spot diseases without affecting the number of tomatoes produced by the plant.