If you are growing tomatoes on any type of black weed control fabric. I might have a solution for your blight problems. Last year Sams club did not have the black weed control fabric they had a sliver colored one. I used it and had no problems all year with any type of what looked like fungus (yellow leaves turning brown and falling off) But this year I went back to the black fabric and guess what? I have the yellow leaves again and brown dried up leaves. Here is what I think might be happening. The black fabric is heating up from the sun and baking our plants. I did have some tomato plants I planted in what became the weed patch and they were protected from the sun and NO fungus and great looking tomatoes. Next year I will try to find some more off white weed control fabric to test my theory.