- Leaf holes typically indicate the presence of caterpillars, which may be picked off the plant. You may also spray rose bushes with a general purpose insecticide to combat caterpillars.
- If your plant is adequately watered and the leaves are still shriveling and dying, aphids may be feeding on the rose bush. Aphids suck nutrients out of the foliage, leaving behind a withered leaf husk. Unlike caterpillars, however, aphids do not chew the entire leaf. Malathion and dimethoate spray products kill aphids.
- Diplocarpon rosae is a black fungus that mottles rose leaves. Infected leaves should be snipped off at the stalk. Application of a fungicide in early spring and a second application when the rose bushes bloom may prevent future outbreaks.
- Mildew creates whitish leaf discoloration. It may spread quickly and completely kill a rose bush in a few weeks. The prompt removal of infected leaves followed by an application of propiconazole may defeat mildew.
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