Agriculture Reference
In-Depth Information
such as a coin with a plant saucer over it. This works only when the ants are seek-
ing sugar, and if it fails, commercial biocontrols are available.
Biocontrols
'Biocontrols' is a term given to a range of biological control methods for dealing
with a particular pest. Examples of biocontrols are the introduction of ladybirds to
combat aphids, or nematodes (microscopic worms that live in the soil) to kill slugs.
They are considered a much better alternative to pesticides as they are completely
organic and don't leave toxic residues behind. If they are used over a large area,
resident predator species starve or move away in search of food, and the balance
of the local ecosystem may be disturbed. In the confines of an average polytunnel,
however, this is less likely to be a problem.
Aphids
Aphids, also referred to in Britain as blackfly and greenfly, are a very successful
group of insects, largely because they breed so very rapidly. Spotted early, they
are not a problem in the tunnel, but if allowed to spread unchecked they can
cause serious damage by distorting growth and spreading moulds. It's worth-
while knowing that each of the many different aphid species feeds on particular
groups of plants, so if you spot a colony in the tunnel, check all similar plants for
further colonies immediately.
Aphids are most likely to take hold on soft, tender growth. This usually means
that they go for the growing tips of plants, but plants that are weak or have been
given too much nitrogen (leading to soft, sappy growth) are also prime targets.
The best defence against significant aphid colonies is a lively community of
predatory insects such as ladybirds, hoverflies and lacewings, which should be
frequent visitors to your tunnel, particularly if you provide plants such as the
poached egg plant (Limnanthes douglasii) to attract them. In severe cases you
can buy ladybird eggs as a biocontrol, but make sure they are a native species.
If aphid colonies are spotted, cover any uninfested plants of the same type with
horticultural fleece to stop them from spreading. If ants are present, you will also
need to deal with them. Spray the insects off the plants (preferably early in the
morning when they are inactive) using a very fine jet of water under quite a bit
of pressure, but try not to bruise soft young plant growth. If this is not possible,
nip out the affected growth and remove it, or bring in a few ladybird larvae from
outside, which is surprisingly effective. Ladybird larvae look completely unlike
the adults. They are about half a centimetre long and have dark grey, segmented
bodies (like little grey alligators) with some yellow spots down each side. Make
sure you can identify these creatures so you don't accidentally eject them from
your tunnel.
