I found a recipe online for fighting the blight from a nursery.
They suggest not watering the pant but watering the ground. Problem is, I can’t control the rain or the dew in the morning.
I use landscape fabric around mine but they still get the blight.
The recipe is:
3 Tbsp baking soda
1 G water
1 Tbsp cooking oil of your choice.
3 drops dish washing detergent
If the blight still grows bump up to 3 1/2 Tbsp baking soda.
Spray only in early morning or evening, not in the middle of the day.
Spray once a week both the tops and bottoms of the leaves until the leaves are dripping.
The baking soda changes the pH to just alkaline enough that the fungus will not colonize.
Yep. That works to some extent, too. I have had excellent results with the copper spray, though.
And the reason to mulch heavily and prune lower branches (that don’t produce tomatoes, anyway) IS to keep heavy rains from splashing soil up onto the leaves and spreading the disease.
If you’re always growing tomatoes in the same spot, that’s an issue, too. You can cover the soil in that area with black plastic and ‘cook’ it for a season, but then you’ll need to add compost and other amendments because cooking it kills off The Good Stuff, too. :(
With blight, as with war and football, the best Defense is a good Offense. :)