Tomatos dont like my wood deck. The deck has not been stained in the last 3 years. Tomato plants grown adjacent to the deck are healthy except for branches, leaves & fruit that contact the deck. If I put a container tomato plant on the deck, it becomes unhealthy, (brown curled leaves, no flowers), until it gets higher than the deck handrails, then it gets green & flowers. Herbs & flowers grow problem free on the deck. We do not use insect sprays. Any thoughts?
It may be a matter of lack of air circulation. Tomatoes are susceptible to a number of foliar fungal diseases which are less severe if the air circulation is good around the plant. It's quite likely that air movement next to the deck is minimal compared to the air above the railings. If it were a component of the deck stain or preservative, you could prevent the browning simply by placing plastic sheeting or something similar between the plant and the deck. However, I suspect that it is the lack of air movement, and that short of moving the plants to a different location, protective fungicide sprays are the solution to your tomato's problems.