Insect pests and diseases can wreak havoc on a rose garden, disfiguring blossoms and leaves and even seriously injuring the plants. Insect and disease prevention begins with proper care. Don't crowd roses together; they need plenty of air circulation to keep leaves and blossoms dry and disease free. Water during dry periods so roses aren't stressed by drought, which can make them more susceptible to disease. Prune diseased and damaged canes. Keep the ground beneath roses weeded and free of old canes and dead leaves, which may harbor disease. If pests or pestilence do attack your roses, act swiftly to deter the threat.
Insecticidal soap mixed with water and sprayed on plants is effective against many common rose pests, including spider mites and aphids. Mix 1 to 2 tbsp. liquid soap with a quart of water. Choose an organic, oil-based soap for best results.
Pyrethrum is a natural insecticide made from the powdered blossoms of chrysanthemums. Dust roses with pyrethrum to rid them of spider mites, aphids, rose bud borers and other pests. Put the pyrethrum in a shaker canister to make it easier to apply.
Spray roses with dormant oil in early spring before the canes leaf out to defeat spider mites. You can purchase dormant oil, or make your own by combining a gallon of mineral oil, 1 lb. oil-based soap (such as castile) and ½ gallon water. Dilute either purchased or homemade dormant oil to the ratio of 1 part oil to 20 parts water, and spray the plant until wet.
Dust roses with powdered sulfur to treat black spot, botrytis, powdery mildew and other rose diseases. Store the sulfur powder in a dry location to prevent caking and distribute over the plant using a shaker with large holes.
Baking Soda, Oil and Water
Mix 1 tsp. baking soda and ½ tsp. oil in 1 qt. water and spray on rose bushes to control powdery mildew.