Gardening Articles for week
16th February 2008
Written by Wally Richards.
UNDERSTANDING INSECT CONTROLS
This hot, dry summer brings many insect pests into our gardens
and onto the plants.
There are beetles chewing on the foliage at night (often we
don't see what is doing the damage when we inspect during
the day, as they are away hiding) Leaf hoppers and whitefly
that flit all around when we disturb a plant. Caterpillars
that are chopping their way through leaves, scale insects
that are sucking on the stems and leaves of plants, thrips
and spider mites rasping away. Mealy bugs releasing their
honey dew and another cause of black sooty mould, along with
aphids and scale.
There are others but generally speaking the ones mentioned
are the most common and destructive.
How much damage do these pests do to our gardens? If their
numbers are high, then a lot of damage to the plants they
prefer. Plants suffer though loss of foliage (less energy
from the sun) sap is sucked causing dehydration and all is
It is surprising how quickly their populations build up and
often we find we have a major problem that did not appear
to exist a week or so back.
Fortunately these days there are a number of remedies that
we can use to keep the pest insect populations under control,
without harming the environment or our health and more controls
are appearing as our understanding widens.
The purpose of this article is to gain understanding of the
remedies, how they work and how best to use them.
Firstly lets look at the man made chemical sprays that are
conventionally used by gardeners and commercial growers. These
are all poisons, some more deadly than others, many have shown
links to cancer and other health concerns that none of us
would like to have. If a poison can kill an insect pest it
can also kill beneficial insects, harm children, pets, wild
life and the user. Plants absorb a poison and if the plant
is one which we eat, there will be a residue left in the plant,
long after the withholding period has expired. The residue
maybe very low but over time the residues do build up in our
The interesting thing with poisoning insects is that over
a period of time the insects become immune to the poison and
thus loses its control of the target pest. All it does is
harm the environment and your health along with a waste of
your dollars. Many pest insects have become immune to most
of the common chemicals available to the home gardener, as
we have been using them for too many years.
The more life-cycles a pest insect has in a season the greater
the chance of resistance to poisons.
Say an insect has a life cycle of 7 days then there can be
about 30 generations in a season.
White fly has a 3 day cycle which may mean 90 plus generations
in a season. Ample generations to become super
pests over a few years. Chemical sprays kill insects and the
ones that are affected die quickly. They are not nice to use
and becoming very expensive.
Aphids have soft bodies and if we take the old, yellow, cake,
Sunlight soap and lather it up in warm water and then spray
the aphids with this what happens? The fatty acids in the
soapy water breakdown the soft bodies of the aphids and they
die over a period of a few hours to a day or two.
Do the aphids become immune to Sunlight soap? Apparently no
as our grandmothers used to take the same soapy water out
of the boiler (after washing the clothes) and throw it over
the roses to kill the aphids. This is a more natural remedy
that will still be killing aphids in a 1000 years time if
Sunlight soap is still available. (Note that liquid soaps
and chemical soaps will not work)
Pyrethrum is one of Natures natural insecticides. It is derived
from the dried flowers of two members of the chrysanthemum
family, C. cinerariifolium and C. coccineum. Pyrethrum affects
the nervous system of many insects when they come into contact
with it. Used in many non toxic fly sprays, you see the results
of flies spinning on their backs as their nervous system is
Some insects such as ants can detect the presents of pyrethrum
and avoid that area, hence it has a repelling effect for some
pest insects. Pyrethrum is very sensitive to UV and freshly
sprayed in an area exposed to UV it will be broken down within
about 2 hours.
To obtain the best advantage from pyrethrum you need to spray
just on dusk so that the spray will be active till next morning.
It is not 100% kill, according to the scientists than have
tested the product and generally found about a 80% kill or
better factor. Because Pyrethrum is broken down so quickly
in sunlight and it is natural to boot, there is no withholding
period on food crops.
Another advantage is Key Pyrethrum (trade name) can be used
at only 1 ml per litre of water making it very economical.
A great natural spray for most insect pests.
Any Problems ring me at 0800 466464 (Palmerston
Web site www.gardenews.co.nz
Another natural product is from the Neem
Tree. The kernels of the Neem Tree contain an oil that has
anti-feeding, growth regulator and repelling properties, besides
being an oil which will smoother some insects such as scale.
The oil does not kill any insects, instead it will prevent
them from feeding or being able to go to the next stage of
development which means they will eventually die.
It would appear the anti-feeding aspect is the most noticeable
and when a pest insect gets some Neem in its gut it never
eats again. Damage stops at that point and over the next few
days the insect dies of starvation. When we use Neem Tree
Oil as a spray we will not have immediate deaths of the pests
but a few days later you will note a marked decline in populations.
One or two repeat sprays about 3 to 7 days apart usually gives
great results. Neem Tree Oil is also broken down by UV and
has up to about 7 days control period. Sprayed on a leaf of
a plant (over and under) it will control those insects on
that leaf that are either chewing, sucking or rasping the
leaf but it will not effect any insects on the leaf next to
it if not also treated in a like manner. This means the spray
does not enter a leaf and translocate to other leaves. To
be effective then, the whole plant needs to be sprayed, over
and under the foliage.
We mentioned before that the oil is obtained from the kernels
of the Neem Tree. This is done by cold pressing the kernels
to extract the oil. What is left of the kernel is called Neem
Cake in India and what we call Neem Tree Granules
These granules still retain a little of the Neem insecticide
properties which can be used to advantage. Sprinkle the Neem
Tree Granules onto the soil in the root zone of a plant where
they break down releasing the properties, which are then taken
up by the roots of the plant.
Any pest insect chewing or sucking on the roots get a dose
of Neem and stop eating. Great for root mealy bugs, nematodes,
grass grubs etc. Because the Neem has entered the roots it
is then translocated up the plant and in some cases to the
foliage. When a plant takes up a substance that it does not
need it works on converting the substance to carbohydrates
or sugars. Plants maybe very efficient in doing this and others
not so good. With the ones not so good, means that the Neem
properties reach the leaves and when an insect attacks the
leaves it gets a small dose of Neem and stops eating. Populations
don't build and you are happy as you have not needed to spray.
This will not work on all plants but appears to work for tomatoes,
(whitefly) brassicas, (caterpillars) lettuce, (black aphid)
apples (codlin moth) roses (aphids and maybe other pests)
cabbage trees (caterpillars) citrus (borer) and likely some
other plants as well. The granules need to be refreshed about
every 4 to 8 weeks.
You can also take a strong solution of Neem Tree Oil say 25
mils into a litre of warm water and water that into the root
zone for an initial dose and then apply the Neem Tree Granules.
Neem Oil sprayed on plants has also been found to be effective
in stopping possum and rabbit damage to plants by a number
of rural gardeners. (Likely because it tastes horrible)
Neem Tree Oil and Key Pyrethrum can be added together for
good results and if Raingard is also applied then the protection
period will be longer as Raingard reduces UV damage.
By the way the best natural control for mites (spider mites)
is Liquid Sulphur sprays.
I hope that gives you a better understanding.
Problems ring me at 0800 466 464 (Palmerston
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