Septoria leaf spot is a very common fungus and something one has to learn to live with by doing the best they can using a number of preventive measures.

The fungus winters in the soil on plant debris, so your planter should be thoroughly cleaned of all roots and debris in the fall. Cover the soil with mulch, use a drip system to water them and try and keep the foliage as dry as possible. The winds you mentioned will help keep the plants dry because the fungus needs high humidity to spread, don't worry about the wind and worry about plant nutrition.

A sickly plant will be more prone to the spread of infection so I try and keep my tomatoes well fed and healthy but this doesn't include excess nitrogen. When Nitrogen is to high there is an increase in severity of parasites which require a host plant to reproduce (septoria is one), and with to little Nitrogen there is an increase in severity of other parasites which don't require the specific host to survive, and all relates to the nutritional requirements of a specific parasite. Reaching the optimal level of potassium on the other hand reduces the incidents of fugal disease drastically, and studies have shown the reduction could be as much as 70%. I won't go into details about fertilizing your plants but recommend looking at what and how you're feeding your plants.

Watch for outbreaks on the low leaves and prune infected leaves immediately, and if rainy humid conditions extend beyond a few days I may spray with a copper fungicide or if it continues to spread I'll spray with chlorothalonil, but more often just pruning infected leaves is enough.

Finally I find some tomato varieties hold up better to Septoria than others. If what you grew the last three years can't hold up I suggest trying something else. I'll give a variety two years to prove it's worth otherwise the seed pack goes in the garbage. No tomato variety is completely resistant to septoria, but some fare better than others. In the 5 or 6 year's Ive been growing mountain magic I haven't had one plant touched by septoria while other varieties next to them were always infected to various degrees. I'm growing 4 or 5 new varieties this year and 2 are from the mountain series "rouge" and "pride" and if they do as well as magic they will become keepers.

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