Pests and diseases - Powdery Mildew

Signs - White powdery mould appears on the leaves, stems and buds. Young growth in particular is affected. The disease is encouraged by the plant being dry at the roots with damp stagnant air around the top.

Damage - Looks unsightly and causes leaves to drop early. If the plant is well established this is a relatively harmless disease. However, care should be taken with younger plants since these may be drastically weakened.

Treatment - A fungal disease so one of the best ways of dealing with it is by good hygiene. Remove all dead leaves in autumn to prevent the spores from over wintering, burn the leaves or take them to the skip rather than use them for compost or you may well just perpetuate the problem.

Like many fungal diseases, this is caused by any one of a whole group of fungi.

Mulch well in spring and autumn with well rotted farmyard manure to prevent the roots drying out. If possible, prune plants so they have an open shape and air can move through the branches.

Horsetail tea. Horsetail (Equisetum arvense) is a pernicious weed which spreads by underground stems that go very deep and form horizontal rhizome systems. This makes it particularly difficult to control particularly on heavy soils where trying to pull it up just breaks off the stems leaving a piece in the soil to carry on. If you have a horsetail problem, there's a bright side to it because an infusion of the weed makes a good fungicide for control of mildew on strawberries and other crops, and checks rust on celery and celeriac.

Collect the horsetail, foliage, stems, rhizomes and all, and for each 28g (1oz) pour on 1.1 Litres (2pt) hot, not boiling, water, and allow to stand for twenty-four hours. Strain off the 'tea' and use undiluted.

Elder spray. This kills aphids, small caterpillars and is useful as a fungicide for mildew and blackspot on roses. The toxic agent is hydro-cyanic acid, so in preparing the spray use an old saucepan.

Gather 450g (1 lb) leaves and young stems of elder prefer-ably in spring when the sap is rising. Place in the saucepan and add 3.3 litres (6pt) water. Boil for half an hour, topping up as necessary. Strain through old tights and use the liquid cold and undiluted. It will keep for three months if bottled tightly while still hot.