Sooty moulds are fungi which cover plant leaves, stems and twigs in a black sticky substance. In the picture below, Powdery Mildew has damaged the fruit which has broken apart the berry skin. The berry skin has leaked sugar which has caused an outbreak of Sooty Mould.
|Sooty Mould and Powdery Mildew on Sauvignon Blanc.|
In most cases Sooty Mould in grape bunches is caused by Mealy Bug, which produce 'honeydew' when they feed on the ripening grape berry. There are several means of treating Sooty Mould. In simple terms, they all boil down to controlling the Mealy bug secreting the honeydew on the plant. Without honeydew the Sooty Mould does not develop.