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.
