Young Blonde Girl With The Rose

Roses are subject to several diseases. The main fungal diseases affecting the leaves are rose black spot (Diplocarpon rosae), rose rust (Phragmidium mucronatum), rose powdery mildew (Sphaerotheca pannosa) and rose downy mildew (Peronospora sparsa). Stems can be affected by several canker diseases, the most commonly seen of which is stem canker (Leptosphaeria coniothyrium). Diseases of the root zone include honey fungus (Armillaria spp.), verticillium wilt, and various species of phytophthora.
Fungal leaf diseases affecting roses are best prevented by choosing to grow cultivars and species known to be less susceptible to attack, and by using a preventative fungicidal spray program (rather than by trying to cure an infection after it emerges on the plant). After disease is visible, spread can be minimized through pruning and the use of fungicides, although the actual infection cannot be reversed. Stem cankers are best treated by pruning out infection as soon as it is noticed. Root diseases are not usually possible to treat, once infection has occurred; the most practical line of defence is to ensure that growing conditions maximise plant health and thereby prevent infection. Phytophthora species are waterborne and therefore improving drainage and reducing waterlogging can help reduce infection.
The main pest affecting roses is the aphid (greenfly), which sucks the sap and weakens the plant. (Ladybugs are a predator of aphids and should be encouraged in the rose garden.) In areas where they are endemic Japanese beetles (Popillia japonica) take a heavy toll on rose flowers and foliage; rose blooms can also be destroyed by infestations of thrips (Thysanoptera spp). Roses are also used as food plants by the larvae of some Lepidoptera (butterfly and moth) species; see list of Lepidoptera that feed on roses. The spraying with insecticide of roses is often recommended but should be done with care to minimize the loss of beneficial insects.