By

Sloane Lane

Black Spot of

Rose

Scientific Name:Diplocarpon r rose

Common Name: Black Spot of Rose

The Life Cycle of

Black Spot of Rose

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 ascomycete in the family

Dermateaceae and is a hemibiotrophic fungus that is restricted to the genus Rosa L. It is spread

primarily through waterborne, two-celled asexual spores (conidia) that require free water to

germinate.

Life Cycle of The Black spot

• 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 as little as 7 hours. Leaf spots begin to show 4-5 days after the initial infection.

Method of Infection

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 variety's.

Cultural conditions that favor disease development include dense plantings, and watering late in the day when water will remain on plant foliage for many hours, and not allowing good air circulation can also contribute to this fungus.

Factors that favor infection

The Host Healthy Rose

Unhealthy Rose Bush with Black Spot of Rose

Description:

Black spot is a nasty

fungus disease of roses.

Infected leaves have

black, rounded spots on

the upper surface of the

leaves. The spots have

feathery or fringed

edges often with a

yellowish halo around

the spots. In severe

infections, the spots are

large and run together.

Eventually, the leaves

turn yellow and drop.

Sometimes, flower

pedals are also affected.

Damage Caused or Symptoms

. Overtime this can produce a weakened bush on which cane dieback and stem cankers can form, and winter injury can become severe and can predispose the plant to 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.

Economic Factors

Treat the bush with preventive sulfur spray in spring, before new growth. The use of sulfur to fight black spot

is well known and proven. The spores won't grow on sulfur but because it

washes off you must repeat the application on a regular basis and

after each rain.

Prevention and

Control

There are also many home-made solutions which different gardeners live by if you choose to go

organic. Many methods being practiced are with the solutions varying from aspirin, backing soda, and milk, and mild detergents that can be mixed

and used as preventive measures.

Organic Solutions