Quantcast Using Soil Sterilants

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AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
only after fully considering potential conse-
persistence in the soil are influenced by (1) its
quences and alternatives. Bare soil erodes both
solubility; (2) the rainfall in the area; (3) the
by water movement and by wind. The loss of
physical and chemical properties of the soil,
soil maybe accompanied by rill and gully ero-
such as texture, structure, and pH; (4) organic
matter; and (5) the micro-organisms in the soil
sion, and the dust problem from wind erosion
may be considerable. Also, water erosion of soil
that are able to deactivate the chemical.
often carries the herbicides with it and may
c. The rate of application and the optimum
time for treatment vary with soil, rainfall, and
severely injure or kill desirable grasses, woody
plants, or other vegetation in downslope areas.
the weed species to be controlled. In most areas,
Mowing existing vegetation may adequately
it is better to make repeated annual applications
maintain a site for its planned use. Maintaining
of soil sterilants at relatively light rates than to
low-growing grasses or other vegetation is al-
rely on a single heavy treatment. Such a mainte-
most always preferable to having the soil bare.
nance dosage results in a smaller annual expen-
diture than a "one-shot" method and keeps
b. There are four major considerations in
chemicals in the surface soil where they can kill
maintaining bare ground:
weed seeds coming in from outside or that may
(1) No herbicide kills all species at reason-
have been dormant in the soil. The full effective-
able rates of application.
ness of some soil sterilants like bromacil, tebu-
(2) Reinfestation results from weed seeds in
thiuron, diuron, and simazine is most evident in
the soil after the herbicide has been leached
the second or third year of use, especially in dry
below the surface.
areas or with deep rooted weeds.
(3) Desirable trees, ornamental plants, and
d. Broadleaf species are usually the first vege-
turf in adjoining areas may be killed or injured
tation to reinfest sterilized areas. Relatively inex-
if surface water drains across treated areas to
pensive supplemental treatments with esters
untreated ones, or it tree roots extended into
2,4-D at 1 to 2 pounds per acre, or other
treated areas.
herbicides in attachment 7, will maintain areas
(4) Bare soil is subject to serious erosion
free of tall vegetation for several additional
where the terrain is steeply sloped and there is
Irears. Make spot treatments of the difficult-to-
enough rainfall to cause runoff. You should
kill plants by hand at rates high enough to kill
meet these problems by using the most appropri-
the tolerant weeds rather than making another
ate herbicide treatment for the situation, and by
general spray treatment.
using soil binding or stabilizing treatments or
e. Failure to get expected control may result
structures to prevent erosion.
from an incomplete distribution of the herbicide
on the soil or from inadequate amounts in the
3-5. Using Soil Sterilants. There is no one
soil solution to effect a kill. A chemical of low
herbicide available that meets all requirements
solubility may be adsorbed in the upper soil
for complete control of vegetation.
layer and not reach deeper roots. This may
a. At practical rates of application, even the
happen in soils with poor underdrainage, in dry
soil sterilants do not always kill all vegetation.
regions, or when the treatment is made at the
There are two major reasons. First, each of the
wrong time. A soluble chemical may leach out
soil sterilants listed in this publication has one or
of the soil before the plant roots absorb a lethal
more plant species that is tolerant to it; and,
dose. This occurs most commonly in sandy soils
second, these herbicides do not behave equally
having excessive underdrainage and with high
well under all environmental conditions.
rainfall, seasons of heavy showers, or under
b. Soil sterilants prevent the growth of green
irrigation. It may result from improper timing of
plants. They do not actually sterilize the soil. To
the treatment. A number of actions can be taken
be effective, a soil sterilant must be soluble
when hard-to-kill species are a problem, or
enough to be carried into the root zone by
where environmental factors reduce the activity
moisture in the soil. Also, it must remain in the
of a chemical: (1) increase the rate of applica-
soil long enough for a lethal dose to be absorbed
tion, (2) use a mixture of chemicals, or
by the plant. A soil sterilant's movement and
(3) repeat the treatment.


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