Download Plant Responses to Herbicide Applications

Unit
Plant Science
Problem Area
Managing Plant Growth
Lesson
Plant Responses to
Herbicide Applications
Student Learning Objectives
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1. Describe the types of herbicides.
2. Explain the selectivity of herbicides.
3. Discuss the time of application of herbicides.
4. Explain the areas of application of herbicides.
5. Discuss the guidelines for applying
herbicides.
6. Understand safety precautions when using
herbicides.
7. Explain Round-up Ready plants and
herbicide applications.
Terms
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Band Application
Broadcast Application
Carrier
Contact Herbicide
Directed Application
Early Preplant Herbicide
Nonselective Herbicide
Postemergent Herbicide
Preemergent Herbicide
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Preplant and
Incorporated Herbicide
Preplant Herbicide
Preplant Surface Applied
Herbicide
Selective Herbicide
Soil Sterilant
Spot Application
Surfactant
Translocated Herbicide
What are the different types of herbicides?
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A. Translocated (systemic) herbicides are taken
into the plant through the roots or leaves and moved
to a sensitive area such as a growing point or
storage organ. Translocated herbicides are
important in controlling perennial weeds with
underground storage organs, but timing is important.
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B. Contact herbicides, also called nontranslocated
herbicides, are not moved within the plant but simply
kill the plant tissue it contacts. Most contact
herbicides are nonselective.
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C. Herbicides can be classified by their mode of
action. The method by which an herbicide kills
depends on how the plant translocates and
metabolizes the chemical.
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D. Some herbicides inhibit lipid or amino acid
synthesis, chlorophyll formation, or
photosynthetic reactions. Other herbicides act as
growth regulators and interfere with normal
metabolism, or disrupt cell membranes.
How are herbicides selected?
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Herbicides are classified according to the way
they destroy weeds. Herbicides can be classified
as selective, nonselective, or as a soil sterilant.
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1. A selective herbicide is one that will kill only
certain types of plants. Most herbicides used on
cropland are selective because they control
weeds while doing little, if any, damage to the
crop. A selective herbicide is not toxic to some
plants because it can be metabolized into a
nontoxic substance.
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2. A nonselective herbicide is one that will kill any plant it
contacts. Nonselective herbicides can be used with growing
crops but extreme caution must be used to prevent crop
damage. Nonselective herbicides are also used in noncrop
areas such as right-of-ways and around buildings where total
control of vegetation is desired. Nonselective herbicides may
have little or no residual activity after application.
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3. Soil sterilants are herbicides that prevent any vegetation
from growing for a period of months or even years. Soil
sterilants are never used on cropland, but rather are used in
noncrop areas where complete control of vegetation is
desired for a long period of time.
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4. Whether a herbicide is classified as selective, nonselective,
or as a soil sterilant will depend on the rate that it is applied to
the soil or plant.
How does the time of application classify
herbicides?
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A. Preplant herbicide is applied before the crop
is seeded and is usually applied as part of
seedbed preparation.
B. Early preplant herbicide is applied 10 to 30
days before seeding and may or may not be
incorporated into the soil.
C. Preplant surface applied herbicide is
applied up to 10 days before seeding and is not
incorporated into the soil.
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D. Preplant and incorporated is applied up to
10 days prior to seeding and immediately
incorporated because it will evaporate or be
broken down by sunlight.
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E. Preemergent herbicide is applied before the
weeds and/or crop emerges but after the crop
has been seeded.
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F. Postemergent herbicide is applied after the
crop and weeds have emerged from the soil.
What are the application areas of
herbicides?
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A. Band application is treating narrow strips with herbicides.
The strip centered on the seed drill, which is usually at the top
of a row.
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1. A Band is usually 10 to 12 inches wide.
2. This is an efficient way to manage weeds by applying
herbicides close to plants.
3. Cotton and corn plants are common crops where band
application is used.
B. Broadcast application is treating the entire area of a field.
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1. No Bands or strips are left untreated.
2. Broadcast application is used with pastures, lawns, and grain
crops that are not in rows.
3. This application is used in places where cultivation cannot be
used to destroy weeds.
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C. Directed application is treating only selected plants or
target plants.
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1. Method primarily used with trees.
2. Small trees to be culled were injected with an herbicide just
above the ground.
3. Directed application has been used in row crops. Newer
technologies with “smart” sprayers only apply herbicides where
weeds are present. These sprayers use computers and photo
detectors to determine the location of each weed.
4. This approach saves money by only spraying where weeds are
present.
D. Spot application is treating only certain areas in a
field or pasture.
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1. Locations where weeds are growing are targeted.
2. Saves in the cost of herbicide and labor to apply it.
3. Used along fence rows, around barns, and in crops where
weeds are in spots.
What are some guidelines for applying
herbicides?
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A. Recommendations: Herbicide recommendations vary
from one year to another. Most states annually release
weed control guidelines. Only herbicides approved for a
particular use should be applied. The rate and timing of
application should comply with the approved use.
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B. Soil Type: The rate of herbicide to use with preplant
and preemergence applications depends on the soil.
Before buying and applying herbicide, determine the
type of soil. Some herbicides are more effective in sandy
soils than in clay and loam soils and vice versa.
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C. Stage of growth: The size and age of both
weed and crop plants must be considered. The
best results will be achieved when the weeds
are small—preferably in the seedling stage.
Larger weeds are more difficult to control.
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D. Form of Herbicide: Herbicides are typically in
a liquid form. Some are mixed with pellets of
fertilizer or other materials for specific uses,
such as in lawns.
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E. A carrier is the material in which the active ingredient
of a herbicide is mixed. Most carriers are water, but
some are oil. A carrier dilutes the herbicide and reduces
toxicity. Carriers provide a from that allows maximum
safety and effectiveness when a herbicide is used.
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F. A surfactant is a material added to herbicide mixes to
assure that the applied material spreads over leaves and
does not bounce off. Surfactants are like soap. Surface
tension between the leaf and herbicide is reduced to the
material spreads over the leaf surface. Surfactants are
sometimes known as wetting agents. In oil-based
sprays, filming agents are used to help assure good
coverage.
What are safety precautions when dealing
with herbicides?
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A. All herbicides must be used only as approved.
B. Do not treat food crops that are near harvest.
C. Properly store herbicides.
D. Keep herbicides out of the reach of children or other
people who are not responsible.
E. Dispose of empty containers properly.
F. Flush skin and eyes with water if contact is made with
herbicides.
G. Know the emergency telephone number in case of an
accident.
H. Protect wildlife and domestic animals.
I. Wear proper personal protection, including clothes,
respirators, hats, gloves, and boots.
What are Round-up Ready plants?
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Weed control practices in soybeans have evolved
over the past several decades. Before the
introduction of herbicides, weed control was
achieved by mechanical and cultural means.
Herbicides began to replace tillage and cultivation
practices as the primary weed control method for
soybeans in the 1960’s, at which time, soilincorporated and preemergence herbicides became
the dominant chemical weed control methods.
Today, roundup-ready plants emerge as a profitable
and efficient means to weed control.
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A. Roundup Ready® soybeans set a precedent
in 1996, as they were the first Roundup Ready
seed product to come to market in the United
States. Since then, other Roundup Ready crops
such as corn, cotton and canola have been
introduced.
B. All are tolerant to over-the-top applications of
Roundup® herbicide—providing post-emergent
weed control.
C. Plants, using biotechnology, are made to
withstand the application of the herbicide
Roundup.
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D. Roundup Ready herbicide works by inhibiting
the production of EPSPS, an enzyme necessary
for the production of amino acids essential for
protein production and plant growth. As a result,
protein cannot be made and the plant system
collapses leading to plant death. This process is
found only in plants.
Roundup Ready plants have been modified
using genetic engineering techniques to
increase its tolerance to applications of Roundup
Ready herbicide.
Review/Summary
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What are the different types of herbicides?
How are herbicides selected?
How does the time of application classify
herbicides?
What are the application areas of herbicides?
What are some guidelines for applying
herbicides?
What are safety precautions when dealing with
herbicides?
What are Round-up Ready plants?