DISEASE
 
   NAME
     Petal Blight
     Itersonilia perplexans

Description
A fungal problem that infects flower and leaves. 

Symptoms
Flowers and leaves form small translucent or brown spots on the margins that enlarge and merge, turning the flower brown. The infected area then rots and is susceptible to Grey Mold. During humid periods black sclerotia may develop in the petals. The infected flower then dries out and persists on the plant unlike unaffected flowers that fall after blooming. 

Source and Dispersal
It is found on other infected plants and the sclerotia may overwinter in the soil or leaf litter. The spores are dispersed by wind.

Favoured Conditions
It prefers warm humid to wet conditions.
	
Affected Plants
It infects a wide range of plants including Dahlia, Chrysanthemum species and Cynara scolymus.	

Non-chemical Control
It is difficult to control but it may be limited by the removal of infected flowers and plants.

Chemical Control
Preventative spraying of a fungicide such as triadimefon is the only way to control the problem. Follow up applications may be required.
Note
Always read the label for registration details and direction of use prior to application of any chemicals.