Powdery mildew is one of the most important diseases of apple in the UK.
- All parts of the tree are affected, including fruits and it reduces yield and quality and repeated severe attacks gradually debilitate the tree.
- On susceptible varieties, such as Cox, mildew levels of as little as 10% mildewed leaves per season are sufficient to significantly reduce yield and quality.
- In the UK most commercial apple orchards receive routine sprays to control mildew.