In this article we talk about rose diseases and their parasites, cryptogamic diseases of roses, how to recognize, prevent and treat our roses.
General information on rose diseases and parasites
Although roses are vigorous and robust plants, they are often prey to various parasites and cryptogamic diseases , many of which are easily fought with modern chemical products; others are very difficult to eliminate and it is therefore advisable to think about preventive actions rather than trying to cure them once they have occurred. The susceptibility of roses to diseases, however, varies from species to species such as gallica, damask, centifolia, wrinkled and moschate, almost all very rustic and practically immune, unlike the hybrid Tea and ground cover, easily attacked by fungi. In the event that diseases arise, it is essential to begin treatments as soon as possible.
However, it should be remembered that a good cultivation method allows you to avoid rose diseases, especially fungal ones, ensuring the plants have the right amount of fertilizer, avoiding excess nitrogen and making sure not to wet the leaves during watering. Poor drainage in the pot or planting hole, a hot and very humid climate and positioning in areas where air does not circulate freely, favor the onset of these diseases.
Cryptogamic Rose Diseases
White Mal or Powdery Mildew :
Rose Diseases Photo (Oidium)
This disease caused by Sphaerotheca pannosa , of fungal origin, attacks roses quite easily and manifests itself as a white-grayish downy powder. It covers young vegetation, the apical stems and the leaves that become yellow or reddish, wither and fall while the buds fail to open. Serious if neglected. Intervention must be timely.
Scab or black spot:
Rose Diseases Photo of Scab
Black spot disease caused by Diplocarpon rosae , one of the most serious rose diseases, practically impossible to cure and eradicate permanently. Of fungal origin, it appears in spring on the leaves in the form of round black spots with yellow-brown halos that continue to grow, leading to a progressive yellowing of the leaves until they fall, leaving the plant bare. Scab rarely leads to death, but the plant suffers a strong loss of vitality. Preventive treatment begins in spring as soon as the first spots appear, carrying out regular treatments with a systemic fungicide . It is necessary, however, that the leaves attacked by the disease are collected and burned immediately, never left on the ground, where the spores of the fungus would remain in a state of dormancy until they resume their activity again the following spring.
Rust
Detail of a rose leaf affected by rust
Small fungi ( Phragmidium mucronatum ) similar to orange pustules that attach to the underside of leaves in spring. At the end of summer they take on a blackish color. Rust first appears on the lower leaves of plants and then climbs the stem to reach the uppermost ones. It causes leaves to fall off and must be burned because, as in the case of scab, the fungal spores can remain in the soil and reappear the following season. It has the same symptoms and consequences as black spot and must be treated preventively in the same way.
Chlorosis:
Leaf affected by Chlorosis
It is not actually a disease, but a state of suffering of the plant due to the excessive presence of calcium in the soil that inhibits the absorption of nutrients. It manifests itself with the yellowing of the leaves and the young shoots, growing weak, are easy prey to diseases. It is treated by modifying the soil with periodic applications of iron chelate.
Rose Pest Diseases
Green aphids or lice:
Rose Plant with Green Aphids
They are the most common insects that infest roses ( Macrosiphum rosae ). Generally bright green in color, but also brown or gray, active from spring to autumn, they live on the most tender organs and suck the sap and produce a honeydew that attracts ants. If not treated promptly they proliferate very quickly. Lice can transmit viral diseases that make the leaves pale as in the case of chlorosis. However, there are many natural enemies of aphids that can help us to eradicate them without having to resort to the use of chemical preparations: first of all ladybugs that can devour thousands of lice in a day; plants rich in essential oils that, if placed next to roses, ‘disturb’ the lice by driving them away, such as lavender, chives, allium, marigolds etc. Finally, the nebulization of macerates of water and Marseille soap, water and nettle or water and tobacco, can help in a natural way to keep lice away.
Thrips:
Image of a Thrips
Insects similar to black flies with four wings, whose caterpillars and larvae live in the buds damaging the flower , nibbling the edges of the petals. Particularly active during periods of great heat. They are fought like aphids.
Beetles and Cetonia:
Image of a Beetle
They nest in the center of the flowers causing serious damage as they devour the stamens and the pistil. It is best to remove them by hand . Even in the larval stage, when they still look like small white worms and nest among the roots, they are extremely harmful .
Scale insects:
Image of a rose affected by cochineal
They are found especially on old and woody stems and on the lower sides of leaves. They appear as small cottony whitish scales a few millimeters wide. If neglected they can cause serious damage, causing the exhaustion of the plant.
Rose sawfly:
Photo of the Rose Sawfly
In the adult stage it looks like a small wasp ( Argae rosae ). It makes incisions in the stems where it deposits eggs . From these, green or green-yellow caterpillars hatch in large numbers that feed on the most tender leaves, leaving only the veins. Once discovered, eliminate the nests and insects manually or burn them. A particular species, the leafminer sawfly, digs deep tunnels inside the stems that become limp and wither .
Red spider:
Red spider photo
These are tiny red insects similar to mites ( Tetranyclus urticale ), easily identifiable. They frequently infect plants placed in positions where air does not circulate and in periods of great drought. If neglected, they multiply very rapidly and can, in addition to seriously damaging the plants, cause major blemishes and malformations to the buds and petals of roses.
