DISEASE

NAME
Black Spot
Marssonia rosae


Description
A fungal problem that is wide spread throughout the world.

Symptoms
Black spots appear on the surface of the leaves and are up to 12mm across. As the blackened area increases in size or melds with another it causes the leaf to curl then turn yellow. The leaves eventually die and fall, defoliating the plant. The fungus also infects the stems causing dieback and loss of vigour in the plant. Affected plants tend to produce smaller blooms.

     

Source and Dispersal
The spores are found on infected plants and fallen leaves and are distributed by wind.

Favoured Conditions
The disease is more prevalent during warm humid conditions with temperatures around 12şC to 25şC.     

Affected Plants
Rose plants with some of the cultivars more susceptible. There is a form of Black Spot(Coniothyrium hellebore) that attacks Helleborusspecies that forms concentric rings and turns the leaves yellow, flowers fail to open and stems die.

Non-chemical Control
Avoid overhead or late afternoon watering and keep foliage dry. Prune off infected parts and burn, heavily infected plants should be discarded.
Space the plant in order to improve air movement and use correct pruning techniques to open the centre of the plant.

Chemical Control
Chemical should be sprayed as the climatic conditions approach ideal and continued throughout that period at regular intervals. There are many chemicals on the market that can be used such as, bitertanol, carbendazim, chlorothalonil, copper oxchloride and zibeb.
Note
Always read the label for registration details and direction of use prior to application of any chemicals.