List of pests and diseases of roses

Pests

• Aphids Macrosiphum rosae – Likely to be found on new shoots and buds, aphids are soft bodied insects 1-2 mm long. Often green but occasionally light brown, and sometimes with wings, they may cover the complete growing tip of the plant. Aphids are most active in spring and summer and multiply at a prodigious rate feeding on the sap of the plant by piercing the plant cells via a proboscis. In large quantities they may seriously retard the growth of the plant and ruin buds. They are particularly damaging to the new shoots with subsequent damage to the emerging leaves which become malformed with much the same appearance as leaf-curl in peaches.
• Two-spotted mite Tetranychus urticae – Previously known as red-spider mite these arachnids prefer the underside of leaves and are difficult to see with an unaided eye. Evidence of their presence is silvering of leaves where the mites have destroyed individual leaf cells. Fine webbing and eggs on the undersides of leaves is further evidence of the presence of Tetranychus urticae.
• Thrips – Thrips are slim-winged insects 1 mm in length, resembling fine slivers of wood or rice. Preferring light-coloured blooms and often appearing in plague numbers, flowers are often left looking scarred, warped, and lustreless.
• Rose slugs - Sawflies are non-stinging wasps in the suborder Symphyta, not flies. They lay eggs in plant leaves or stems with a saw-like ovipositor. There are three species that commonly cause damage to wild or cultivated roses: The bristly roseslug is found in Europe, Siberia, and many areas of North America. The larva is pale green, up to long, and covered with hairlike bristles all over its body. It looks like a caterpillar but that term, strictly speaking, only applies to the larvae of moths and butterflies. It skeletonising the underside of leaves, with several generations per year. The European roseslug is found in North America and Europe. The larvae is more slug like, up to, and skeletonises the upper surface of leaves with only one generation per year. The curled roseslug larva is pastel green on the back, marked on the thorax and abdomen with white dots, and up to long. It frequently coils up like a snake. After skeletonising entire leaves except the main veins, it pupates in the pith of canes, with up to two generations per year in North America.
• Caterpillars ' – The moth Lozotaenia forsterana is a prominent pest of roses. The caterpillars are green, up to 15 mm long, and can be found boring into buds or within curled leaves. When disturbed the caterpillars move swiftly, dropping to the ground on a fine thread. Damage is chewn leaves and flowers and buds with "shot holes".
• Curculio beetles
• Japanese beetles - This species, introduced to North America in 1912, is now an endemic pest in the eastern United States. Adult beetles emerge from the ground in early summer and join into swarms for four to six weeks, devouring blooms and skeletonising foliage on roses and many other garden plants. Japanese beetles can be partially controlled, albeit slowly, by spreading milky spore bacillus on the lawn areas where the larvae live. The popular pheromone-baited traps may do more harm than good by attracting beetles from a wide area.
• Scale insects
• Leaf cutting bee Megachile species – Leafcutter bees are 6-16 mm long and mostly black with bands of light-coloured hair. They chew pieces from the edges of leaves. The pieces are regular in shape, circular or oval. Damage is not often significant.
• Nematodes
• Rose chafer Macrodactylus subspinosus – The rose chafer is common to North America, and emerges in late May to mid June. These beetles form aggregations and feed upon foliage, buds, flowers, and fruit of roses and other ornamentals.
• Metallic flea-beetles' Altica species – The small, shiny and metallic Altica'' beetles have thickened hindlegs adapted to jumping, similar to fleas. The insects are 3 mm long and chew holes of irregular shapes in young leaves and buds. As the leaves enlarge so do the holes.

  Diseases

Bacterial diseases

• Crown gall rot Agrobacterium rhizogenes – This disease is characterised by large lumps at the base of the plant stem or on roots. Galls may appear higher on stems as the disease progresses. Galls are soft compared to surrounding plant tissues. The pathogenic bacteria enter the plant via a wound. If the disease affects the plant whilst it is young the plant may be affected to the degree where it will not produce blooms. All affected plants wilt readily and grow poorly.

Fungal diseases

• Black spot Diplocarpon rosae syn. Marssonina rosae – Marssonina rosae causes black spots on leaves. The spots, which may be as much as 12 mm across, are generally circular and have an irregular edge often with a yellow halo. Leaves frequently turn yellow and fall early. Sometimes new leaves are produced, and these may also become affected. Continual defoliation will cause weakness, dieback or death of the plant. Some very susceptible species may have stems affected with a considerable reduction in plant vigour.
• Powdery mildew – P. pannosa produces a very fine, powdery coating on the surface of buds and leaves. Significant cases have stems and particularly thorns, infected. Attacks on young leaves and buds will cause deformity with retardation of growth. Infected buds will fail to open. The disease is likely in hot, humid weather, with fungal spores overwintering on the stems and fallen leaves.
• Downy mildew Peronospora sparsa – Peronospora causes purple-red to dark-brown spots with irregular margins on the leaves, however, often angular. Stems, petioles and flower stalks can split and spotted with purple marks. Buds, sepals, petals and calyces can be affected and will present purple spots. New growth affected will be deformed. The disease is spread by wind.
• Rust Phragmidium mucronatum – Rose rust appears as yellow patches on the surface of leaves, with orange pustules of spores underneath the leaf. The fungus is spread by wind. Affected leaves fall prior to healthy ones and plants may be defoliated in serious infections.

• Anthracnose Sphaceloma rosarum – Spots caused by this fungus originate from a point where leaves are water soaked, usually unnoticeable at first, until they turn black with a very distinct defined edge. As the spots enlarge the centre becomes grey and may fall out resulting in a shot-hole appearance. Defoliation may occur but is often not serious.
• Grey mould Botrytis cinerea – On roses grey mould is primarily a disease of the flowers and buds, leaves are infrequently attacked. Infected buds rot on the stem and infection may progress down the stem. On petals Botrytis cinerea produces pink rings.
• Verticillium wilt Verticillium dahliae
• Sooty moulds Alternaria species – Sooty mould appears as black, dry powder on leaves similar to chimney soot. Many sooty moulds grow on the honeydew produced by sap-sucking insect such as aphids and soft scales. Alternaria does no direct damage to plants but surface cover of leaves will reduce the plants capacity to photosynthesise and may create an unsatisfactory plant appearance.
• Canker Leptosphaeria coniothyrium and Cryptosporella umbrina – Cankers present as small yellowish or reddish spots on bark slowly increasing in size. Leptosphaeria coniothyrium turns brown, increases in size, and may eventually girdle the stem. The tissue within the infection begins to dry out and shrink, presenting a shrivelled appearance. If the disease infects only part of the stem, growth above the canker will continue. If it girdles the stem, however, growth will cease and the stem will die.

Nematodes, parasitic