Symptoms of the black spot of the rose Diplocarpon rosae are visible on the leaves in the form of light brown, then blackening spots.The spots are round and irregular and often blend together.Around the spots of the leaf tissue turn yellow. Heavily infected leaves fall offSymptoms also appear on the shoots in the form of reddish, slightly raised discoloration.
The shrub, defending itself, produces new leaves before the arrival of autumn, as a result of which it freezes more easily in winter. The fungus hibernates on fallen leaves and infected shoots.The optimal temperature for the development of the disease is 15-27 ° C.Above this temperature, the growth of the fungus is inhibited.Resistant varieties should be grown. Plants should not be watered on cloudy and rainy days. Fallen leaves must be removed and infested shoots cut.Chemical protection should start in June.
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The weather conditions this year also favored the development of rose rust. It is caused by several species of fungi of the genus Phragmidium.At the turn of April and May we can observe the symptoms of this disease on the underside of the leaf blade and on young shoots in the form of very small yellow-orange spots.Infected leaves and shoots are deformed.
Soon, the next stages of this disease appear on the underside of the leaf, first with orange spore clusters, the so-calledand then dark brown clusters of spores.Leaves with symptoms of infestation dry up and fall off massively.The fungus hibernates on infected shoots and in fallen leaves.
The prevention of this disease consists in removing infected shoots and collecting and destroying fallen leaves.When watering, avoid wetting the leaves, because the remaining moisture promotes the development of not only rust, but also other diseases.After finding the first symptoms, spray the plants with fungicides.
