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Welcome to New Zealands Plant Portal. Wally Richards Weekly Garden Tips & Advice.


Gardening Articles for week ending
16th February 2008

Written by Wally Richards.

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 not well.
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 fatty tissues.
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 destroyed.
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.

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Any Problems ring me at 0800 466464 (Palmerston North 3570606)
Email wallyjr@gardenews.co.nz
Web site www.gardenews.co.nz

Garden Pages and News at www.gardenews.co.nz
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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) rhododendrons (thrips)
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 North 3570606)
Web site www.gardenews.co.nz

Garden Pages and News at www.gardenews.co.nz
Shar Pei pages
at www.sharpei.co.nz

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