Plant roses far enough apart and prune out stems from the center of each plant so that there is plenty of air circulation. This can help prevent black spot, rust, and powdery mildew.
To help get rid of powdery mildew, you can clean off your roses thoroughly with a strong spray of water from a hose in the summer. Hosing should be done when powdery mildew starts, but after black spot season is over, and should be repeated every three to five days. This cleaning will also wash off most aphids. Then it is essential to pick up all fallen parts (petals, leaves, and cuttings) since they can harbor fungi and pests that will reinfect your plants. This debris should not be composted but should be disposed of.
One good spray for black spot consists of a tablespoon of baking soda, a tablespoon of vegetable oil, and two drops of dishwashing liquid in a gallon of water. Be sure to shake well before spraying. Another spray consists of a clove of garlic chopped and added to a gallon of water. Or, you can get Soap-Shield
Fungicidal Soap already made, which controls black spot, powdery mildew, and rust; and is rain resistant, all natural, and environmentally friendly. When spraying, be sure to get the undersides of the leaves as well as the tops, and do this early on a sunny day so the water has plenty of time to dry. Spray roses every week or two until there is no more sign of disease.
Fungi and aphids can remain over the winter and come back to life again in the spring. To control that, remove all the old mulch from around the roses at the first sign of spring and replace it with fresh mulch or compost, although compost will help to smother and kill the problem much better than mulch. Continue to remove the old material once a month until winter.
Aphids can leave honeydew on roses, resulting in the growth of sooty mold, which attracts ants and blackens leaves. A severe infestation can lead to drying and curling of new leaves, and can even prevent buds from opening. After hosing, Sta-Home lady beetles (ladybugs) and/or
Green Lacewings can be released on the rose plants to eat the aphids. You can fill your garden with live bugs that arrive in the mail.
Aphids attack when a plant's resistance is low, and regular fertilizing can help to prevent this. But, over fertilizing can also bring aphids, so moderation is best. Seaweed is best for adding potassium, and rabbit droppings are high in nitrogen. (If you don't live near the ocean, you can get kelp meal). Dried coffee grounds and ground egg shells make good fertilizer for roses. For those that don't drink coffee or just need more coffee grounds, some coffee houses are happy to give theirs away. Epsom salt (magnesium sulfate) promotes stronger, sturdier stems, richer green foliage and deeper, richer colors in roses.
According to Rose Magazine, you can make your roses unpalatable to aphids and other pests is by spraying them with a solution of a half water and half Listerine. You can also make your own insecticide by adding one garlic bulb to two cups of water. This should be put in the blender, or you can purchase crushed garlic. The mixture must set for a day or two and then be strained before use. Add the garlic water to a gallon of water and spray it on the tops and bottoms of leaves.
Planting garlic, onions, chives, marigolds, petunias, lavender, or chrysanthemums in with your roses will help to keep pests away.