How can I solve this quince problem?

Q

I have a patio quince in a pot. It is two years old and gets the same problem every year – the leaves have a white powder than then turns black. What is it?

Rita Staines, via email

AThe problem on the leaves of your quince is a common fungal disease called powdery mildew that usually occurs when a plant is growing on dry soil but the air around the leaves is humid or damp.

It is often quite difficult to avoid the disease, particularly if we are going through a dry patch, but unless the infection is widespread it is unlikely to do much long-term damage to the plant.

However, plants in pots are more vulnerable because even in wet weather their compost isn’t necessarily getting as much rain as is available. If the pots are nicely displayed on a patio they might not be subject to as much air movement

as plants in the open, and as a consequence humidity levels can be quite high around the foliage.

If the spread of the mildew isn’t too severe then it is possible to control it by removing all the infected leaves, and making sure that the affected plant is regularly and adequately watered.

However, if the infection is widespread then it might be worth spraying with a fungicide. The fungicides tebuconazole (Bayer Fungus Fighter Concentrate), tebuconazole with trifloxystrobin (Bayer Fungus Fighter Plus) and triticonazole (Scotts Fungus Clear Ultra and Scotts Fungus Clear Ultra Gun) are approved for the control of powdery mildews on ornamental plants.