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Hardly any disease is as dreaded by rose lovers as the star soot. The reason: Many roses are susceptible to infestation and very few varieties are completely resistant, which is why the disease is very common. In addition, the Sternrußtau is a very persistent fungal disease that can be difficult to combat. And she does not just attack roses. Other plants such as laurel and oleander are affected by the pathogen. Mostly, the disease occurs only on outdoor stands.
The black spot (Diplocarpon rosae) is an ascomycete fungus (Ascomycota) from the subsection of the genuine ascomycete fungi (Pezizomycotina). The disease is also referred to as black spot disease.
The Sternrußtau pathogen overwinters on fallen leaves on the ground and on the bark of the plants with so-called apothecia - these are fruiting bodies of the ascomycetes. From there, he infects the plants in spring. An infection can also be done by pouring and rainwater. How quickly the fungal spores spread, then depends on the sensitivity of the plants. Wet and cold weather, waterlogging, clayey and humus-poor soils also favor the spread.
In the spring to summer, more fungus spores are produced on the affected leaves - the so-called ascospores. Under favorable conditions such as dew and rain, the disease spreads explosively.
Sternrußau is quite easy to diagnose: large black-brown fruit storage - so-called Acervuli - are on the top of the infected leaves. The fruiting bodies are distributed unevenly or arranged in concentric circles. They contain so-called conidia - a certain form of spores of fungi. These in turn ensure the further spread of the fungus on the plants. The conidia are further spread by splashing water, unfavorable cultural measures or by insects.
The first symptoms can usually be seen in April or May: First, the leaves of the diseased plants begin to turn yellow and eventually fall prematurely. In heavy infestations with star soot, many roses are often leafless already in midsummer.
At the beginning, often only black spots are visible, later the whole leaf turns yellow
Since the metabolism and energy exchange of the plants only takes place to a limited extent in the case of a disease with a blackspot, the plants are greatly weakened. Leafless plants rarely bring forth new flowers; new shoots can no longer form wood and therefore no longer mature. The incomplete wood maturity has due to the loss of leaves after heavy infestation by Sternrußtau a reduced frost hardness.
Similar symptoms as on the leaves are found in rare cases on other green parts of plants and fruits. On the immature wood of the annual shoots form first violet-red irregular patches, which turn black in the further course of disease and also contain fruiting bodies to spread the disease.
Frequently affected plants
The star-soot pathogen settles with great preference on all roses - but especially strong shrub roses are affected.
Laurel, oleander and other garden and house plants can also be attacked by the fungus. Indoor plants, which sometimes suffer from lice in the low-season, are particularly at risk because of their already weakened immune system. In rare cases, the fungus spreads to orchids, camellias, green lilies, thick leaf and various types of cactus. Sometimes vegetables and fruits such as cucumbers or apple trees are attacked.
In order to prevent fungal attack, you should pay attention to rosacea diseases such as star soot when buying new plants on resistant and resistant varieties. Varieties with good resistance properties against star soot are for example 'Angela', 'Dortmund' and 'Yellow Dagmar'.
The planting place should not be too damp and shady, as this favors an infestation. In addition, it is advisable to put the plants at a certain distance from their neighbors. This ensures better ventilation and ensures that the plants can dry off quickly after rain. When watering, be sure to water only the roots so as not to leave the mushroom with a damp climate on the leaves. Also, a watering in the late evening is not recommended, since the plants - except in summer - can not dry overnight.
By appropriate nutrient supply you increase the resistance of your plants to fungal diseases. A balanced and caliber-fertilized effect in many species preventively against Sternrußtau.However, avoid excessive nitrogen intake.
Since an existing infestation is difficult to combat, it is worthwhile to prevent the susceptible plants from the beginning of May several times with plant tonics. If your roses were already affected with a blackspot last year, such treatments are also recommended, because the plants often suffer the consequences of an infestation next year and are happy about a little strengthening. Above all, the application of home-made herbal preparations such as horsetail, comfrey or garlic broth has proven itself in the fight against star soot. These preparations are applied several times from the leaves of the respective plants at intervals of about two weeks.
A self-made Horsetail slurry can be used preventively to strengthen the plants
Cut and clear your roses regularly and carefully dispose of fall foliage in autumn, as otherwise the mushroom can hibernate here. Even in summer, infested leaves should be disposed of immediately in household waste.
A good ventilation of your interior leads to a quick drying of the leaves of indoor plants and thus reduces infestation with Sternrußtau. In general, avoid too shady and damp locations for your plants in the house.
Check your plants regularly from the beginning of May for a possible infestation. Already at first signs you should immediately cut off sick leaves and infected shoots with a sharp knife and dispose of them with the household waste. Do not put the sick parts of the plant on the compost, because they may re-infect next year. After each work step, disinfect the garden tools used to prevent spreading the fungus.
Another option is to treat the affected plants with fungicides (fungicides) such as Rose Mushroom-free Saprol, Mushroom-free Ectivo and Duaxo Rosen. These preparations are effective if you perform the treatment three times at intervals of seven to 14 days. It is important to ensure a good and uniform wetting of the leaf underside, so that the spores of the fungus can not germinate again.