I found something online that said, the old timers use to spray rusty water on their plant 100 years ago to control blight. For years I have been trying to find something that really works so I decided it is worth putting it to the test. We typically get blight here in TN 3rd week of July every year, 3 plants died and all the others have blight.
I saved about 20 food cans from the kitchen and burned the glue and varnish off in a fire. I put all the cans in a 5 gallon bucket of water and let the rust for 3 weeks. I poured the rust water though a rag to filter out anything that might plug up the sprayer. I sprayed all the plants with rust water and gave each plant a drink of rust water every day for a week. Some of the plants that lost most of there leaves are growing new leaves. Some plants have blight worse than others but all the plants seem to be getting better.
3 of the 18 plants have ripe tomatoes so I just have to wait and see how it goes. I started new plants in pots to transplant to the garden soon. I hope one way of the other we still have tomatoes on the kitchen table for another 3 months. If I can keep 1 or 2 plants alive and producing 1 tomato per day that will be good.
My grandfather use to put about 20 rusty nails in the hole when he planted tomatoes. I need to find a bunch of rusty metal. I read online IRON and COPPER are both good for blight control. I have tried copper with no luck but iron seems to work.