is a Herbicide?
are substances that are used for
killing all types of plants, especially noxious weeds. Herbicides
into 8 different groups including one group that is "ungrouped."
are chemicals that kill plants or inhibit their growth.
are varied and theoretically as numerous as the processes essential to
life. Herbicides are most often and most effectively used
cultural practices in a turf weed management program. The choice
specific combination varies with agronomic, ecological and economic
Do Herbicides Really Work?
work in many different ways. In order to be
effective, herbicides must first be applied to a plant. After the
applied, it must then be retained on the leaf's surface. Then it
through the water filled space that is around the cell. Once the
moved through the water filled cell or space, it must then enter a new
through a lipid like membrane. When it has passed through that
herbicide will usually reach its target. The target is usually an
Finally when the herbicide reaches the target it will bind to and
target enzyme. The herbicide must take a different
approach. It must
target the weed and not the plant or crop. Then the crop and not
itself must break it down.
Why Do Herbicides Kill Plants?
They kill the
plants by causing a build up of
toxic substances where the toxic compounds usually stay at low
the target site the herbicide causes substances to build up and then
plant. This is how herbicide glyphosate works. In other
death of the
target plants seems to occur from deregulation of the very carefully
process of cell growth. This is how herbicides such as 2, 4-D
plants just grow them selves to death. Herbicide resistant plants
farmer reduce expenses indirectly. Although seeds are a small
farm costs a farmer may save money if the new seeds are paired with
that are cheaper because their patents have expired and have to compete
generic versions. The biggest potential lies with designer seeds
new more efficient proprietary chemicals, according to Charles
executive director of the Board of agriculture at the National Academy
Sciences. Herbicides resistant seeds may also help to solve the
“carryover” in which the chemical lingers in the soil and is toxic to
crop to be planted. The new plants will almost certainly be
multiple resistance's to give the grower even more choices to match his
For chemical companies herbicide resistance is a smart way to protect
current markets or expand into new ones. Most of the major
manufactures are engaged in some research to develop herbicide
plants. The volume of herbicide use in the U.S.
is actually declining because
the most recent weed killers are more potent. Some types of
soil applied herbicides.
Use in Forestry
herbicide uses in forests are in some instances, a cost
effective tool for the control of vegetation. Landowners use them
different ways to increase the forest productivity. Forestry
help prepare sites for tree planting, reduce unwanted vegetation, and
conditions for prescribed fires. They will also reduce
herbaceous weeds so that newly planted trees are given a boost for
reproduction. They may be applied to improve the growth rates
stands by selective removal of non crop trees. The vast majority
are used for growing pines although some are applied for herbaceous
timber stand improvement in hardwood forest.
Many people have the
misconception that all compounds whose name ends in “ cide” such as
insecticide, rodenticide, or fungicide can be lumped together as danger
toxic chemicals, and unsafe at any application level. This is
vast majority of agriculture pesticides and is certainly not true of
herbicides. Table 1 provides the acute toxicity of the active
several forestry herbicides for comparison some other
common chemicals. The table lists the
LD50, which is a rating system for chemical toxicity. A low LD50
a small amount of chemical is toxic and is a more dangerous
other hand, the larger the LD50 the less toxic the chemical is.
forestry herbicides have active ingredients that are less toxic than
And, the active ingredient is diluted to make the herbicide product
sold on the
market. All over the counter formulations of the products listed
have LD50 above 1700 mg/kg and so are therefore less toxic than
|LD50 of Active Ingredient mg/kg
McNabb, Ken, Environmental Satey of Forestry
Herbicides, March, 1997.
Alberta Agriculture, Food and Rural Development, How Herbicides Work
of Action, copy write 1996, 56 pgs.
By: Chris Henderson