First, prune away and discard ant affected leaves and clear any fallen leaves and plant part form below the plants.  Feed them right away with Espoma Holly-tone organic food.  Make sure any sprinkler systems are NOT spraying the plants with water.  Start a preventative spraying program with a sulfur or copper fungicide.  Nutrition and hygiene can go a long way to preventing leaf spot in the future but the fungicide spray may be need to get it under control.