Black spot, one of the most feared diseases of roses, is caused by the harmful fungus Diplocarpon rosae. In this article we will tell you how to recognize this rose disease and what you can do about it.
Blackspot is very easy to diagnose
Diagnose blackspot
The disease mainly occurs after damp and cool summers and is quite easy to diagnose: the rose petals initially show isolated, later more and more round, black-brown leaf spots. As the name of the disease suggests, these have a radiating edge. The leaves usually turn yellowish around the large, quite irregular spots. The affected leaves initially turn yellow and eventually fall off completely. In the event of a severe infestation, the rose can lose almost all of its foliage and become immensely weakened. For this reason, the fungus should be treated as soon as possible, because not treating it can even lead to the death of the rose in the worst case.
How to combat blackspot effectively?
When it comes to fighting, you don't have to hope for the winter, because the fungal spores hibernate in the rose leaves and thus ensure a renewed infection next year. Therefore, affected leaves should be removed immediately and disposed of with household waste, including those lying on the ground. Thoroughly rake up fallen leaves and under no circumstances throw them on the compost - this would only create a new focus of infection. Many advisors recommend fungicides, i.e. chemical antifungal agents, to combat it. However, these are usually not necessary - at least if you have noticed the infestation early on - and also have a negative impact on the natural balance in the garden. Natural, self-made sprays based on horsetail, comfrey or garlic have proven very effective against blackspot.
Prevent blackspot sensibly
These remedies - above all the field horsetail broth - can also be sprayed preventively to prevent an infestation before the leaves sprout. This measure should be carried out in the spring, when the leaves are just beginning to unfold. Mist the roses for several days at a time, but it should be dry and reasonably mild. You can also prevent blackspot by good ventilation of the rose - thanks to an optimal location, the right planting distance and regular pruning - as well as balanced fertilization.
tips
Plant garlic and other bulbous plants (e.g. ornamental onions) around the rose, as these act as a deterrent to pests and also disinfect their surroundings.