Agriculture Reference
In-Depth Information
mould around the base, and in advanced cases you may see pinhead-sized black
spheres forming. Lift and use the affected crop immediately, but do not compost it.
White rot is practically impossible to eliminate but at least you can stop it from
spreading. Follow the soil hygiene recommendations as for club root (see page
164).
Whitefly
Whitefly are found in clusters on the underside of leaves, and fly up in clouds
when disturbed. Damage tends to be slight, with some yellowing and stunting of
growth, but the real danger in a polytunnel is the sticky honeydew that the
whitefly secrete. This can act as a trigger for sooty moulds, which are far more
damaging than the whitefly themselves.
If whitefly are found, light infestations can be dealt with by spraying the colony
with insecticidal soap early each morning, over several days. More serious infes-
tations can be dealt with using the biocontrol Encarsia (a tiny parasitic wasp),
but this is not an instant fix, and if you intend to use it you should avoid using
any insecticides at all, since residues on the foliage may kill the biocontrol when
it arrives. A better option while you wait for your Encarsia may be to use a 'dust-
buster' (hand-held vacuum cleaner) around the plants during the afternoon,
which will at least reduce the numbers of active adults.
Woodlice
Woodlice are generally beneficial creatures because they break down decaying
vegetable matter quickly and browse on moulds and fungi, but they can be a
nuisance in the tunnel because of their tendency to attack soft young growth.
There are no products to control them without also killing beneficial insects, so
the best strategy is to keep the tunnel free of debris of all kinds, and make sure
that any compost used as a soil dressing is well rotted, as woody material will
cause a woodlouse population explosion. To reduce the numbers of woodlice in
trouble spots in your tunnel, leave bait such as cooked potato (or, better yet,
moistened ground rice) out overnight with a plant saucer or tile on top of it.
Woodlice attracted to the bait can be removed the following morning.
