Pests and diseases - Caterpillars
Signs - Leaves stripped, or eaten from the outside edge inwards.
May not always be easily visible as they can be well camouflaged. "Frass"
may be seen, tiny black balls of excrement. More cunning and smaller types
"mine" leaves between the upper and lower surfaces, others build
a dense web of silk to protect a small colony that feeds on the plant
within the web.
Damage - Young leaves can be eaten away and more mature plants are left
with unsightly holes.
Treatment - Leave them for the birds or pick off caterpillars by hand
as soon as you see them. If you can't bring yourself to kill them, I move
them from where they usually are on the young delicate succulent leaves at the
top of the plant to the larger more mature leaves elsewhere. This however
becomes a daily job as they climb back again!
For really heavy infestations consider using the
biological control based on a naturally occurring bacterium called
Bacillus thuringiensis, which stops the caterpillar feeding and only
infects caterpillars.
Pyrethrum, Malathion
and Derris can be used to deal with heavy
infestations.
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.
