MY NEIGHBOUR called me across to his garden this week, to look at a plant he was worried about. It turned out to be an azalea, its leaves covered with a dusting of white, powdery fungus.

There’s a lot of it about – my phlox are the same, as are the Michaelmas daisies and the courgettes. I suspect the roses and gooseberries of being affected too, though since they’ve lost all their leaves, it’s hard to tell.

I confidently pronounced that my neighbour’s plant had mildew, caused by the wet, miserable summer, and suggested there was little he could do about it but wait for the plant to produce new leaves next year, giving it a good feed of rhododendron and azalea fertiliser in the spring to get it started again.

In a way I was avoiding the issue by not giving him a more precise diagnosis.

There are two types of mildew commonly seen in gardens, caused by a number of different species of fungus which all look very similar – white powdery fungus on the foliage (upper or lower surfaces or sometimes both) with discoloured, yellowy patches on the upper surfaces.

But powdery mildew is caused by dryness at the roots, while downy mildew is encouraged by wet, humid conditions at the roots. Both are made worse by humidity and poor air circulation around the plant.

There are chemical treatments for mildew; fungicides containing mancozeb for downy mildew and fungicides containing carbendazum, triforine with bupirimate, or sulphur for powdery mildew. Better though to treat the underlying causes, which are often cultural – ensuring adequate water at the roots throughout the growing season and maintaining good air circulation around the foliage by increasing planting distances and ensuring gaps between plants aren’t filled with weeds.

In the greenhouse, open vents and doors whenever possible and avoid overhead watering of plants. Keep a close eye on your plants and remove any affected leaves as soon as mildew is spotted, to prevent it spreading.

Mildew spores can over-winter in the soil, so clear up any fallen leaves beneath affected plants, bagging and binning them rather than putting them on the compost heap.

On a more cheerful note, the atrocious weather has done nothing to spoil our autumn-fruiting raspberries, which are cropping prolifically this year. They are a variety called Joan Squire, which we planted a couple of years ago and which have been a huge success.

The canes are tall, up to six feet in height, and they crop over a long period (from September to December last year) producing large, tasty fruits that would be ideal for freezing if we didn’t eat them all as quickly as they ripen.

Jobs for the gardener this week...

Prune rambling roses by cutting down to ground level growths that have flowered this year. Tie in new growths as near to horizontal as possible to encourage the production of next year’s flowering side shoots.

Take out summer bedding as it goes over. Fork the ground over and add some organic material before planting out winter or spring bedding.

Remove fallen leaves regularly from ponds and pools – they will pollute the water if allowed to rot.