Rose Black spot is also known as Diplocarpon rosae. The fungus Diplocarpon rosae is the causal organism of rose black spot, Diplocarpon rosae is classified as an ascomycetein the family Dermateaceae and is a hemibiotrophic fungus that is restricted to the genus Rosa L. It is spread primarilythrough waterborne, two-celled asexual spores (conidia) that require free water to germinate.
• Black spot fungus over winters on infected leaves, or on the plant and on dropped leaves.• It can also remain in infected stems.• In the Spring, the fungus produces spores which are carried by rain splashes to new bushes, starting the infection on new leaves.• Spores are produced throughout the growing season, causing repeated cycles of infection.• Young, growing leaves are particularly susceptible.• The fungus is spread by wind, driven rain, splashed irrigation water and on garden tools.In warm weather the fungus can affect leaves that have been wet for aslittle as 7 hours. Leaf spots begin to show 4 -5 days after the initialinfection.
Leaves are most susceptible while still expanding after bud break. The fungus spores must be immersed in water continuously for seven hours for germination and infection to occur. Fungal spores can be spread by splashed water, or fallen leaves that may disperse the fungal pathogen. The fungal pathogen is present only in the lesion, but its damage extends throughout the leaf. The spot lesions are often small and rarely kill the rose branches, but these are extremely important in the survival of the fungal pathogen over-wintering from season to season. This fungal pathogen can be spread to surrounding plants, including citrus trees, ornamentals, and some other garden varietys.Cultural conditions that favor disease development include dense plantings, andwatering late in the day when water will remain on plant foliage for manyhours, and not allowing good air circulation can also contribute to this fungus.
Description:Black spot is a nastyfungus disease of roses.Infected leaves have black,rounded spots on theupper surface of theleaves. The spots havefeathery or fringed edgesoften with a yellowish haloaround the spots. Insevere infections, thespots are large and runtogether. Eventually, theleaves turn yellow anddrop. Sometimes, flowerpedals are also affected.
. Overtime this can produce aweakened bush on which canedieback and stem cankers can form,and winter injury can becomesevere and can predispose the plantto insect attacks, and other diseases.
The Rose Industry over the years have been able to find measures to keep their field losses down with preventive measures, and routine disease management. This disease is less of a problem in greenhouses where relative humidity can be carefully controlled. Susceptible landscape roses must be sprayed frequently with fungicides to keep the disease under control. Fortunately for rose growers many breeders are constantly striving to produce disease resistant plants and many of the roses introduced during the past decade have shown a remarkable improvement in overall resistance to infection.
Treat the bush with preventive sulfur spray in spring, before new growth. The use ofsulfur to fight black spot is well known andproven. The spores wont grow on sulfur but because it washes off you must repeat theapplication on a regular basis and after each rain.
There are also many home-made solutions which differentgardeners live by if you choose to go organic. Many methods being practiced are with the solutions varying fromaspirin, backing soda, and milk, and mild detergents that can be mixed and used as preventive measures.