We’ve heard from several people concerned about rose pests. So we turned to the expert, Jim Lang, Sonoma County’s longtime master gardener, rosarian and rose judge. Here is what he suggests, partially based on information from American Rose Magazine.
Aphids, mites, scale and whiteflies:
Use orange oil cleaner at a ratio of one teaspoon per gallon of water. Fill a squirt bottle with the mixture and spray on both sides of the leaves. Good coverage is important. Wet the leaf surfaces to the point of drip. Spray as often as is needed when insects are present. Avoid spraying when temperatures are going to be above 85 degrees. But if you feel you must, spray in the early evening when it is cooler. Spray off with water if the daytime temperature is going to be over 85 degrees to prevent leaf burning.
Soap spray. Mix half a teaspoon of mild dish soap or Dr. Bronner’s pure castile liquid soap, in any fragrance, and one teaspoon cooking oil in a one-quart sprayer filled with water. Spray liberally over entire plant, making sure to hit the undersides of the leaves.
Blast with water. Aphids can be dislodged from plants by a strong jet of water. Just be careful to not use too strong a spray on tender young plants and seedlings.
Snails and slugs:
Beer. Fill an empty tuna can, cat food can or small cottage cheese or yogurt container with cheap beer at room temperature. If there’s a bit of beer left over in the can or bottle, don’t pour it out. Use it for the slugs and snails. Dig a hole wide and deep enough to set the container into the soil. Slugs and slugs are attracted to the yeast in the beer and will crawl into it and drown. If there’s no beer to be had, and you have white wine, use that instead. Be sure it’s also at room temperature. And make sure it’s not the good stuff!
Handpick. Not for the squeamish, but it gets the job done fast. Use a flashlight and collect them at night. Around 10 p.m. is when they usually come out of hiding. Then you can do whatever you want with them once you’ve caught them. Chickens love them.
Diatomaceous earth. Apply a ring of about an inch wide around roses, taking note that it doesn’t get wet. Once wet, it loses its efficacy. Slugs and snails prefer not to cross abrasive surfaces.
Powdery mildews, blackspot and rusts:
Baking soda spray. Mix one tablespoon baking soda and one teaspoon cooking oil in one gallon of water and put the mixture in a spray bottle. Apply liberally, covering the entire plant. Repeat as needed.
Sanitation. Remove the infected leaves and destroy them. Do not compost them. Keep the ground under and around the roses free of leaves, debris and weeds.
Cold water. For powdery mildew, spray the affected leaves with cold water early in the morning and allow leaves to dry in the sun. Start spraying as soon as you see the slightest hint of a white powdery substance developing on the leaves.
Controlling insects and diseases is a difficult and time-consuming job. If you find that you’re not making any headway with any of these problems, it might be worth thinking about replacing the infested roses with another type of plant.