That looks like rust, a fungus.
Organic fixes:
baking soda, 1 tea spoon/ quart of water. spray on.
copper sulphate, read lables.
fungacidal soap sprays;
garlic sprays, 1/2 cup minced garlic, 1 quart of water. let sit 24hrs, strain, spray.
sulphur, one of the best natural sprays. it is low in toxicity.
micro kill, a citric based killer. great success
Remove affected leaves if possible.