Last week I sprayed my tomato plants with a copper based organic fertilizer. It was the first time I'd sprayed anything in my garden for years and I did it because I'm convinced fungal problems will persist in tomato plants this year.
I was reticent to use something with copper, even though it's organic, it can affect aquatic life, which doesn't sound good to me.
I've decided to switch to a biological control that I feel is safer, one brand is called Serenade. It won't negatively affect beneficial insects and it won't harm humans or pets. Serenade is applied as a liquid and is sprayed on all parts of the plant. It uses something called Bacillus subtilis to attack the fungus preventing the disease from taking hold.
The key to battling any fungal issue is to spray BEFORE signs of damage are seen.