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Insecticides, as the name
implies, are substances that are meant to kill six
legged creatures called insects. Some of them will also
kill those with eight legs such as
spider
mites
(technically, miticides do that job better). And, if not
used properly, insecticides can also kill four and two
legged creatures...so, take care! |
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Formulations |
Insecticide come in a
wide variety of chemical formulations but the most
commonly used in the home landscape are liquids,
dusts and granules.
Of course, liquids
are most commonly applied with a sprayer or,
sometimes, out of a pale as a soil drench. They may
also be injected directly into trees with special
equipment.
Dusts are best
applied with a spreader made for that purpose. Since
these are such light particles, it is easy for the
wind to blow them around and they could blow back
onto you. Duster equipment will help to minimize
this problem.
Granules are similar
to what you see in a bag of fertilizer. Small,
roundish pellets that are easily spread with drop or
broadcast spreaders.
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Categories of
Insecticides |
There are many ways to describe the substances we use as
insecticides. Some of them have to do with the way they
do the job of killing while others describe their
chemical classification. Here are some of the more
common ones:
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Spectrum - More
traditional insecticides fell mostly in the Broad
Spectrum type which would kill anything and
everything that it either touched or was consumed
by. In the early days of chemical insecticides, this
was thought to be a great idea. Imagine spraying
once and killing all your insect enemies at once. Of
course, this proved to be too good to be true.
Eventually, we figured out that we were also killing
the beneficial insects and that only made the
problem worse. Also, many of these types of
chemicals stayed in the environment for years and
affect a lot of so called "non-target" organisms
too.
As we enter the 21st century, more and more
insecticides are touted as narrow spectrum products.
They are meant to kill a very limited group of
insect pests and have very short active lives. This
is much better for the environment but they require
the user to have a lot more knowledge. They need to
be able to properly identify the specific pest and
the best time to attack it. No more "spray and pray"
philosophy.
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Inorganic Compounds
- Until the early to mid 1900s, there were only a
handful of substances available to farmers,
orchardists, greenhouse growers, and others for the
control of insect pests. Such nasty chemicals a lead
arsenate, nicotine sulfate, hydrocyanic acid gas and
kerosene emulsions were used in the fight against
insects.
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Chlorinated Hydrocarbons
- Around the 1930's, the chemists got busy and
created a lot of new types of chemicals that seemed
to do a good job of killing insects. Perhaps the
most famous of these was a little product called DDT
which worked wonders against insects and even
promised to eradicate mosquitoes that carried
malaria in the tropics. Chlordane and benzene
hexachloride were valued for their long term
effectiveness. Chlordane could be measured in the
soil ten years after a single application.
Of course, once again, unforeseen consequences
reared their ugly heads. All of a sudden eagles and
other birds started to decline. For a long time,
nobody knew why until someone discovered high levels
of DDT in the birds and other animals. Then, they
found out that the DDT caused the birds to lay eggs
with very thin shells that collapsed under little
pressure. Chlorinated hydrocarbons were also found
to accumulate in animals at the top of the "food
chain" in a process called bio-accumulation.
The Environmental Protection Agency (EPA) finally
took DDT off the market. In a few decades, low and
behold, the eagles and other birds began to make a
comeback. That was great but there is some ongoing
debate about the impact of DDT on the mosquitoes and
the malaria deaths in third world countries.
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Organophosphates -
These are another group of compounds that make up
the active ingredient for many of the common
insecticides on the market today. Generally, they
are chemicals that act on the nervous system of
animals including insects and, if misapplied,
humans. They can kill either through absorption by
the skin and mucus membranes or by being ingested
i.e. stomach poisons.
Unlike in the past, these compounds must be studied
thoroughly for both effectiveness and environmental
impacts before they are approved by the EPA. In the
end, however, they are still compounds intended to
kill forms of animal life. So, safety precautions
and proper application techniques are listed on the
label of every product. Still, with misapplications,
serious problems can still arise.
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Microbial Insecticides
- We have learned how to turn naturally occurring
insect diseases against the critters that are
bothering our plants. The most common microbes used
in the battle with insect pests are bacteria which
are available in dusts, wettable powders and liquid
forms. These would include Bacillus thuringiensis
or Bt which is used against
caterpillars and
Bacillus popillae sold as milky spore disease
for control of
Japanese beetles.
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Botanical Insecticides
- As the name implies, these are insecticides that
come from the world of botany i.e. plants. As part
of their natural defenses against insects, certain
plants create chemicals that are poisonous. We have
either extracted these chemicals from the plants
themselves or learned how to create them in the
laboratory and use them in insecticides. Common
botanical insecticides include rotenone, pyrethrum,
nicotine, ryania and sabadilla.
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Systemic Insecticides
- Systemic insecticides are a relatively recent
addition to the arsenal of plant managers. The idea
is to get the chemical into the vascular system of
the plant so that, when the insect feeds on it, the
insect will die. Animals have a nice circulatory
system that spreads blood throughout the body.
Inject a chemical into a vein and it can quickly
move to all parts. Unfortunately, plants do not have
exactly the same system. However, they do have pipes
which can be used in a vaguely similar manner and
that is where systemic insecticides come in.
Since the plant's vascular system is not the same as
an animals, to get good coverage of the entire
plant, the systemic product must be introduced
through multiple sites. Sometimes, the product is
mixed with large amounts of water which are poured
over the root system. It is then taken up by many
different roots and spread to the various branches
and leaves. Another approach is to drill several
holes around the base of the tree trunk and, under
pressure, deliver the insecticide into each one of
the holes.
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Oil Based Insecticides
- Highly refined petroleum oil products are used as
insecticides. Unlike other products, they do not
poison the insect but, rather, they smother it. The
idea behind
horticultural oils is that they are
sprayed onto the insect and clog up their breathing
pores.
Oil based insecticides fall into two broad
categories. One is called dormant oil. These are
oils with a thicker viscosity which are applied
during the time when plants are without their
leaves, thus dormant. They are meant to cover the
likes of scale insects or the eggs of others that
overwinter on the trunks of trees. These products
are sprayed during a warm spell in the winter so
that they will spread properly. They must not be
used while the plant has leaves or they will cause
the death of the leaves.
The other type is called a summer oil. These are
products that are "thinner" or more dilute that may
be used while the plants have leaves. Again, they
spread over the insects and smother them.
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Note: We
have provided some general information and
observations on this topic aimed at the home
gardener. Before you take
any serious action in your landscape, check
with your state's land grant university's
Cooperative
Extension
Service for the most current,
appropriate, localized recommendations. |
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