The main enemies of roses are aphids, sometimes red spiders or mealybugs, as far as animals are concerned; by fungal diseases, the ‘white spot’ disease caused by powdery mildew, the black spot disease caused by Marsonia and Rust.
Aphids appear very early in spring, from April, on young shoots, where they cause the leaves to wrinkle; a little later on the cocoons, where they can cause an abortion. It is necessary to start anti-flea treatments as soon as these insects appear, as they multiply incredibly quickly. Most commercial insecticides treat against aphids and at the same time against the mealybugs or larvae produced.
Red spiders, whose presence is detected with a magnifying glass on the underside of the leaves, mainly in dry weather, cause the leaves to yellow and fall off. Many times orange larvae and red adults are distinguished simultaneously.
Mealybugs or kermes are presented under the aspect of small waxy or grey shields hanging on the branches. In the event of a serious attack, they cause the rose bushes to weaken.
Treatments against aphids should be carried out every 15 days.
Treatment of fungal diseases is more effective in terms of prevention than cure. They should therefore be started early and followed up frequently to cover the young leaves as they develop. the most common diseases are:
- White disease (oidium) gives off a greyish white powder on the first leaves and buds. Effective products are sulphur based.
- The black spot disease (Marsonia) forms diffuse, rounded, purplish-black spots on the upper side of the leaves. This causes the leaves to fall off and the rose bushes to become defoliated.
- The rust forms smaller, more angular and more numerous spots, also on the upper side of the leaves; it then generates small orange spots that swarm on the underside of the leaves. Its condition causes the leaves to yellow and fall off.
All of them are treated with fungicide products, being difficult to remove.