Sunday, June 24, 2007

CHEMICAL CONTROLS: INSECTICIDES

CHEMICAL CONTROLS: INSECTICIDES
The surest way to control most of the insects and
similar creatures that threaten your vegetable crop is
by using a chemical insecticide. A word here about
terminology: In horticultural language the terms
"pesticide" and "insecticide" are not
interchangeable. A pesticide is any form of chemical
control used in the garden; an insecticide is a
specific type of pesticide used to control a specific
situation — to kill insects. A herbicide is a different
kind of pesticide with a different application — it's
used to help control garden weeds. These
distinctions are important, because using the wrong
one will cause havoc in your garden. For instance, if
you use a herbicide instead of an insecticide you'll
lose your entire crop for the season. It's also
important to keep separate equipment for use with
each kind of pesticide.
Insecticides are chemical products that are
sprayed or dusted on the affected crops. The type you
spray on is bought in concentrated form, then
diluted for use with a hand sprayer or a spray
attachment fitted to the end of your garden hose.
Dust-on insecticides are powders that you pump on to
the plants. Spraying is preferable because it gives
more thorough coverage, and it's easier to treat the
undersides as well as the tops of leaves and plants
with a spray. You can also apply insecticides directly to
the soil to kill insects under the soil surface — this
technique is known as applying a "soil drench."
Used correctly and responsibly, insecticides are
not harmful to humans or other animals. They are
toxic, but the toxicity levels are low, and their
residual or carryover effect is short — the longest any
of the insecticides commonly used in the home
garden will remain on the plant is about 14 days.
Malathion, for instance, has the same toxicity level
as Scotch whiskey and breaks down faster. As to any
long-lasting hazards that may be involved —
nobody knows if hazards exist or what they might be;
we don't know what the long-lasting hazards of any
product might be. The choice of an organic or a
synthetic pesticide is a matter of personal opinion.
If you know all the options you'll be able to make your
own choice.
Commonly used insecticides
The insecticides listed below for use in your home
vegetable garden will provide effective control of
garden insects with minimum hazard. Remember,
though, that most insecticides are poisons and must
be handled as such.
Diazinon. This is an organic phosphate, and it's an
effective insecticide for general use. Diazinon is a
contact poison. Its toxicity is low, and it's a good
control for underground insects that attack the roots
of cabbage family plants, onions, and radishes. You
can get it as a wettable powder or in liquid form.
Malathion. This is also a phosphate insecticide; it
kills sucking insects like aphids. Its effects are not as
long-lasting as those of some other insecticides,
but it's effective and safe in use. It's available as a dust,
a wettable powder, or a liquid.
Sevin. This is also known as carbaryl and is
another safe material for use in home gardens. It's an
effective control for many leaf-eating caterpillars
and leafhoppers, and is available as a wettable
powder or a dust.
Bacillus thuringiensis. This is an organic
insecticide. It's a bacterium that is considered
harmless to all but insects, and you can buy it under
the brand names of Dipel, Thuricide, or Bactur. It
controls cabbage worms and other caterpillars and
is available in wettable powder or liquid forms. This is
the choice of many gardeners who prefer not to use
chemical insecticides.
Cause and cure: Be sure you've got them right
Because an insecticide can't distinguish between
friend and foe, it's your responsibility to make sure
you're eliminating the pest, not the friendly insect
that's out there working for you. Let's say, for
instance, that aphids are attacking your cabbage
plants, and you use carbaryl (Sevin) to try to get rid of
them because you know carbaryl is a relatively safe
insecticide with a short residual effect. You've
overlooked the fact that carbaryl has to enter the
insect's stomach in order to kill it, and since the
aphid's mouth is inside the cabbage plant, none of
the insecticide is going to enter the insect through the
mouth and reach its stomach. Ladybugs, however,
love aphids and are most helpful in keeping down
their numbers. So when the ladybug eats the aphid,
the carbaryl on the aphid's body enters the ladybug's
stomach and kills it. Despite the best intentions in
the world, you've killed off the useful insect and left
the pest unharmed. In fact you've done the pest a
favor by killing off its enemy — a ladybug can put
away hundreds of aphids in a day.
Carbaryl can also be toxic to bees, and bees are
important to your garden because they pollinate most
fruiting vegetable crops. To avoid killing the bees,
spray in the late evening when the flowers are closed.
This way you kill the destructive pests but protect
the bees.
If you use an insecticide you must always be
aware also of how long its residual effect is going to
last. A residue of insecticide left on the plant when
it's harvested is poisonous. The residual effect of an
insecticide that you use in your vegetable garden is
likely to be fairly short, but the effect may vary from
one type of crop to another. And because the effect
is not long-lasting, you can't spray as a preventive
measure; you have no way of knowing which pests .
are going to attack your plants before they're actually
on the scene.

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