This pathogen appears in the first months of spring and has its maximum in the months of June. The optimal conditions for the development of this mycelium are the presence of water and temperatures ranging from 18 to 24 °.
It manifests itself with the formation of small yellow spots on the upper side of the leaf, while in the lower part, yellow powdery lumps can be seen. Over the days these spots become darker and darker. This disease, if present massively on a plant, causes its vegetative stasis and yellowing. Rust almost never causes, however, the immediate death of the plant, which slowly deteriorates, completing the vegetative cycle.
The main plants affected by this disease are: fir trees, clematis, geranium, rose, peach.
For the easy occurrence of the ideal conditions of the mushroom, the defense must be done in a preventive and repetitive way. The active ingredients most used in the fight are fungicides such as copper and zinc-containing products, such as zineb and ziram. Products to be sprayed in case of illness every 10-15 days. and as a preventive every six months.
There rust of roses it was first described and identified in 1665 and is widespread all over the world, particularly in North America and Europe. For this plant it is certainly not a pathology of primary importance except in specific pedoclimatic areas. The mushroom, in fact, needs specific temperatures and a particular degree of humidity for the spore germination, the progress of the infection and the survival.
It can become a frequent pathology in very cool and high humidity areas, such as alpine areas. The mushrooms underlying the development of the rose rust they are nine and belong to the genus Phragmidium. However, only P.mucronatum and P.tuberculatum become habitual pathogens in cultivated roses (for example in the cut flower industry).
Some species of roses are particularly subject to this pathology: tea hybrids, climbing hybrids, perpetual hybrids and other types especially characterized by broad and leathery leaves. Even the subjects used as rootstock can be sensitive: for example, Rosa Alba, dog rose, Laxa rose. The presence of an unsuitable rootstock can cause strong attacks and defoliation against the rose bush, especially in late summer.
Usually the first symptoms appear on the basal leaves and spread upwards until the climatic conditions are optimal for its development.
If we live in an area with predisposing climatic characteristics, we therefore pay particular attention also to the rootstock chosen by the nurseryman. Eventually we can also focus on resistant plants reproduced simply through apical cutting.