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Herbicide use
Although herbicide use is not to be taken lightly, the threat of
noxious weeds to the ecosystem of Gilpin County is very real, and
herbicides are often the only realistic way to control weeds with
deep root systems, such as leafy spurge, canada thistle, and yellow
toadflax. It is also sometimes the only way to get a larger weed
infestation under control.
Gilpin County works hard to minimize the use of herbicides for
weed control. All weeds are spot-sprayed, and there is no blanket
or aerial spraying of herbicides. We also work on educating the
public, in order to encourage the early detection and eradication
of new infestations - a new infestation is a perfect time to hand
pull weeds. Where biocontrols (insects that eat the leaves or seeds
of a noxious weed) are feasible, these are used as well. The ultimate
goal of the weed program is to stay on top of weed infestations
while they are small, and to lessen the need for herbicides.
We recognize that some people are extremely chemically sensitive,
and work with them to notify them of dates of spraying (Registry
of pesticide sensitive persons). We further encourage anyone
concerned about spraying near their house to "adopt" the
roads nearby by pulling any weeds in the area (if there are no weeds,
no spray will be used).
Risk analyses of use of herbicides
http://www.fs.fed.us/r3/projects/ro/ea-noxiousweeds/ea-weedsappa.html
Assessing
health risks from pesticides from the EPA
Pesticides
and ecological risk assessment
Facts on herbicides
Colorado Environmental
Pesticide Education Program
National Pesticide information
center - this website gives easy to understand information,
as well as environmental fates of pesticides.
Pesticides
in perspective
Using
herbicides safely and herbicide toxicity
http://teamarundo.org/control_manage/docs/glyphosate_aqua_risk.pdf
Pesticides
and water quality
The information below comes from Forest
herbicide toxicity from Alabama Cooperative Extension
Toxicity
Many people have the misconception that all compounds whose name
end in "cide," such as insecticide, rodenticide, or fungicide,
can be lumped together as dangerous, highly toxic chemicals, and
unsafe at any application level. This is simply not the case for
the vast majority of agricultural pesticides and is certainly not
true of the herbicides used on right of ways and public lands.
Table 1 provides the acute toxicity of the active ingredient in
several herbicides for comparison to some other common chemicals.
The table lists the LD50, which is a rating system for chemical
toxicity.
A low LD50 indicates that a small amount of chemical is
toxic and is a more dangerous substance. Likewise, the larger the
LD50 the less toxic the chemical.
Most of the herbicides used on public lands have active ingredients
that are less toxic than caffeine. And, the active ingredient is
diluted to make the herbicide product sold on the market. All over-the-counter
formulations of the products listed in Table 1 have LD50s above
1,700 mg/kg (milligrams of chemical per kilogram of body weight)
and so are therefore less toxic than aspirin! Even so, we still
limit their use to the minimum necessary to prevent the spread of
noxious weeds.
Table 1. The Relative Toxicity of Commonly Used Herbicides
| Trade Name |
Active Ingredient
|
LD50* of the Active Ingredient
mg/kg |
| Arsenal |
imazypyr |
5,000 |
| Garlon |
triclopyr |
630 |
| Oust |
sulfometuron methyl |
5,000 |
| Roundup |
glyphosate |
4,320 |
| Tordon |
picloram |
8,200 |
| Velpar |
hexazinone |
1,690 |
| Weedone |
2,4-D |
375 |
| For Comparison: |
>
|
| |
Table Salt |
3,750 |
| |
Aspirin |
1,700 |
| Malathion |
(insecticide) |
370 |
| |
Household bleach |
192 |
| |
Caffeine |
200 |
*LD50 is the dose that is lethal to 50 percent of a test animal
population, expressed as milligrams (mg) of chemical per kilogram
(kg) of body weight.
How can this be so? How can a chemical with such low toxicity be
so effective at killing plants? Imazapyr, for example, has an LD50
above 5,000 mg/kg, making it practically non-toxic. Yet this compound
is a very effective herbicide and can control many of the largest
trees. The secret to understanding this apparent contradiction comes
from realizing that herbicides work on biochemical pathways that
are specific to plants. For example, only plants photosynthesize
(produce food from carbon dioxide and water), so, if a compound
inhibits one or several of the steps in the long biochemical pathway
that is photosynthesis, that compound is then toxic to plants. At
the same time, this compound may have no effect on animal systems
because the biochemical pathway for photosynthesis does not exist
in animals. As another example, some herbicides work on amino acid
pathways that are specific to plants and not found in animals. All
of these types of compounds can be very effective herbicides yet
are safe for animals because the biochemical basis for toxicity
does not exist.
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