I need advice controlling these pests and fungi on watermelon

My watermelon children have been affected by Alteria leaf blight and I’m looking for ways to stop the leaves from turning brown. Any suggestions ?

Research says that "Organic gardeners are limited to sprays of captan or copper fungicides". Not entirely sure what those are, or if they're truly natural treatments. Apparently the fungus can live in your soil and contaminate next year's crop of melons, so if you have some melons actually planted in the ground be sure not to use the same spot next year.