Gardeners are being warned to be extra vigilant after the summer weather created a boom in powdery mildews that destroy fruit and vegetables.
The fungal disease kills and maims apples, blackcurrants, gooseberries, grapes, courgettes, marrows, cucumbers, peas, roses, honeysuckle, rhododendrons and azaleas. It also causes problems for farmers because it attacks sugar beet and barley.
“This is a bumper year for powdery mildews – we’ve had a dry summer, with a bit of wetness and then dry again,” said Guy Barter of the Royal Horticultural Society.
“These can kill but usually debilitate and weaken the plants. In vegetables this can reduce the size and total amount of produce and in fruit it kills off some of the shoots and can damage the plants.”
There have already been widespread cases of mildew in gardens and allotments but these are likely to increase as the mildew season peaks around now, said Mr Barter. And Britain’s forests are also suffering. “The warm wet summer seems to have produced a really prolific yield of oak mildew in the past month to six weeks,” said National Trust wildlife expert Matthew Oates.
Gardeners should spring into action at the first sign of white mildew on the leaves, stems, flowers or fruit of a plant, Mr Barter advises.
There are no approved fungicides for gardeners to use on vegetables although there are for fruit and flowers, but it is best to ask at the local garden centre to identify the most suitable, experts advise.
There are approved fungicides for farm crops and farmers typically spray at “first sight”, so the main problem posed to mainstream agriculture by mildew is the high cost of the chemicals – although organic farmers suffer along with gardeners.
Gardeners can take steps to minimise the risk of attracting powdery mildew and slowing its spread.
Watering the plants regularly makes them stronger and so builds up their resistance to disease of all kinds. Removing infected leaves helps slow the spread, while gardeners should also avoid using too much nitrogen fertiliser because this promotes the soft leafy growth on which garden pests thrive.
Gardeners should also look to thin out growth where possible to increase the airflow or to plant further apart.