Time of year brings two common tomato leaf diseases

I have tomato plants with leaves are yellowing, spotting and browning out from the bottom up. What can I do?
This is the time of year that two common leaf-spot diseases appear on tomato plants. Septoria leaf spot and early blight are characterized by brown spots on the leaves.
Septoria leaf spot usually appears earlier in the season than early blight and produces small dark spots. Spots made by early blight are much larger and often have a distorted “target” pattern of concentric circles. Heavily infected leaves will eventually turn yellow and drop. Older leaves are more susceptible than younger ones, so these diseases often start at the bottom of the plant and work upward.
Mulching and caging or staking helps keep plants off the ground and less vulnerable because air circulation is better and foliage dries quicker than in plants which are allowed to sprawl. Mulching also helps prevent water splashing and carrying disease spores to the plant. Removing heavily diseased leaves from the plant also help remove a source of some of the spores.
Some years tomatoes will develop foliar diseases even when all recommend cultural practices are followed. In these cases, fungicides are helpful. Fungicides are preventative and non-systemic.
Therefore, thorough coverage of both upper and lower leaf surfaces is important to stop the spread of the disease.  Also, reapply fungicide if rainfall removes it. Plants usually become susceptible when the tomato fruit is about the size of a walnut.
Chlorothalonil is a good choice for fruiting plants because it has a zero-day waiting period, meaning that fruit can be harvested once the spray is dry. Chlorothalonil can be found in numerous products including Fertilome Broad-Spectrum Fungicide, Ortho Garden Disease Control, GardenTech Daconil and others. Be sure to start protecting plants when the disease is first seen. It is virtually impossible to stop it on heavily infected plants.
For more information contact the OSU Extension Center, 14001 Acme Road, at 273-7683.