Either stake or cage tomatoes shortly after planting. Remove the first three or four suckers while they are still small. When staking tomatoes, loosely tie stems to poles using soft materials such as cloth or old stockings. Blossom end rot is a common problem here especially during dry years. This is not a disease but a physiological rot caused by a calcium deficiency.
Calcium chloride is sold at most garden centers under the name stop rot.
In wet years or with overhead irrigation, tomatoes can be infected by septoria and gray leaf spot. These diseases can defoliate plants and cause fruit to sunscald. To prevent these diseases, avoid overhead irrigation late in the day and spray with a fungicide containing chlorothalonil.