Rose Platter: save tomato leaves for Roses
Black spot on roses is a fungus that loves damp weather. Tomato leaves contain solanine, a chemical that inhibits black spot diseases. Save your tomato leaves when you are pruning. Grind up two cups full of them, and mix them into a half gallon of water. Stir in a couple of teaspoons of cornstarch or buttermilk to help it stick. You can keep this mixture in the fridge, and spray it on your roses once a day.
Water your roses with a slow soak at ground level. Don’t sprinkle them from above, as wet leaves are more susceptible to black spot.
From: 2 Minutes a Day for a Greener Planet. Marjorie Lamb.