When damage first appears, treat all soil around the roses with 5 percent diazinon granules or diazinon liquid. If you use granules, lightly water them in. Spray the foliage, and particulary the teminals or tips of the rose stems, with a recommended insecticide on a regular basis for the rest of the growing season. If a severe infestation occurs, one or two additional applications may be necessary to bring the midge under control. The color is usually black with narrow, white rings circling the rear body.
Sawflies are likely to be a problem on roses in areas where wild roses are present.
Damage to roses is caused by the larva girdling the tender growth or new rose stems, causing the tips to droop. The resulting damage to the rose stem is distortion of the stem and foliage dying at the tips. Eggs are deposited inside the tender growth of the rose stem by the adult's ovipositor, so some control can be had with a systemic insecticide when the telltale drooping of the canes is first noticed. The egg-laying period is usually about two weeks before the last killing spring frost and can last through midsummer. Diseases Powdery mildew, blackspot, anthracnose, rust and verticillium wilt are all caused by fungi.