Botrytis cinerea (Grey mould)

The principal leaf symptom of Botrytis cinerea observed on mature plants (figures 1 and 2) is light brown to beige spots surrounded by a marked yellow halo (figure 3). The sources of inoculum is from senescent flower petals falling on the leaves, hence the English name of the disease  "dead-blossom leaf spot."
 
Stem cankers starting from senescent leaf petioles are also observed (figure 4.). Botrytis cinerea occasionally causes flower rot (figure 5). This disease occurs frequently in France. It first appears on leaves, then stems and finally on the flowers.
 

Figure 4	Figure 5	Figure 6

 
Botrytis cinerea is easy to identify. It rather rapidly produces grey, fuzzy mould on the infected tissues. Sclerotia are rarely seen. This grey mycelium consists of numerous conidiophores and conidia produced during sporulation (figure 6). To induce sporulation, put some samples in an airtight container or in a plastic bag containing a damp paper towel. This will provide the required humidity for the formation of these structures. 

 
For further information on Botrytis cinerea, please have a look at the fact sheet of this airborne fungus.