I find that our tomato plants do great until late June to mid July each year, then no matter what, the plants gets sick, slow down, and eventually die or become almost non productive. So our strategy this year will be to get as much fruit as possible to set early to reach full size before the end of June. Then no matter what happens to the plants, the fruit should ripen to give good quality tomatoes.
My theory is that when the night time lows reach somewhere in the 70's that conditions are just too favorable for the various diseases and the plants succumb. I may try placing a few plants under an awning or roof to keep them out of the rain, to see if that prevents the rampant spread of disease during those hot months. So far nothing has really worked, though some years replacement plants will give a good fall harvest. IMO a secondary factor comes via the piercing bugs that walk all over the plants, spreading disease where ever they walk. This year we may place a few plants under mesh to see if that both controls the bugs and slows the disease as well.
Eclectic gardening style, drawing from 45 years of interest and experience. Mostly plant in raised beds and containers primarily using intensive gardening techniques.