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Citrus Weed Control By Tim Braun
Ask citrus growers in California or Arizona other than an organic grower “What herbicide do you use?” and the answer
will probably be Round Up. The use of glyphosate (Round Up) for citrus weed control is world wide. Herbicide use reports
in Arizona show glyphosate use in citrus at 14 to 1 over other herbicides. There are several reasons for this and the main
reason is that glyphosate works in more weed control situations than other methods.
Glyphosate is a substituted amino acid formulated to be accepted by weeds as a herbicide. The glyphosate compound is
allowed by the weed to bind very strongly with a vital enzyme. This enzyme is needed by the weed to produce proteins that
are responsible for the formation of nearly 35% of the dry weight of weeds. Once the glyphosate compound binds with this
enzyme in the weed the enzyme doesn’t function. The loss of the enzyme’s activities usually results in the death of the
weed. Animals do not have this particular enzyme that glyphosate can bind with in their system. This glyphosate substituted
amino acid is specific for binding with this specific enzyme in weeds.
After the researchers found this compound that would bind with and stop the enzyme from functioning they had to find a
way to get the glyphosate to the enzyme. This particular enzyme is located in the growing systems of the weed. These
parts include new shoots, new root tips, young buds and meristem cell areas of growth.
In the weed’s body food or sugar is produced in one location and the energy in the sugar or food is used or stored in
growth areas and storage areas. There is a name for these growth and storage locations in the weed. Growth and storage
locations are called “sinks“. The storage areas “sinks” where water soluble sugars are changed to water insoluble starch
that can be stored include the weed’s roots.
When trying to kill weeds in the past, contact weed killers like petroleum oils were used. This contact weed control
method only killed young seedlings and other annual weeds that don’t have the type of roots that can support the growth of
new shoots. Disking and other forms of cultivation give the same results as contact herbicides. In some cases repeated
applications of contact herbicides or repeated disking and cultivation could kill these roots by cutting off their food supply
and starving them to death.
The weed’s body locations of sugar or food production is where photosynthesis takes place. Photosynthesis combines
sunlight energy with carbon dioxide and water to produce sugars and oxygen. This food production takes place in
chlorophyll containing cells. Photosynthesis takes place in most of the mature aerial parts of the weed. These places are
called “sources”. When the sugar reaches a storage area like the roots an enzyme causes the water soluble sugar to form
molecular long chains. The chains of sugar molecules are called starch which is not water soluble. Because of this
insolubility of starch the water diffuses to an area in the plant where it’s needed leaving the starch in the storage or “sink”
When food is needed by the weed in growth areas another enzyme causes the starch’s long chains to separate forming
water soluble sugar. The sugar is water soluble again and this storage area becomes a “source” sending sugars to “sinks“.
Depending on the enzyme, storage areas in weeds can be either a “sink” or a “source“.
Entering the weed and traveling to the target enzyme has to be done with the help of the weed. Glyphosate has to get to its
target using the weed’s translocation system. In order to do this the glyphosate must change its chemical formulation to
take advantage of the weeds system that moves materials around inside the weed. Glyphosate becomes a “hitchiker” in the
weeds vascular transport system.
Glyphosate must first get to the vascular system inside the weed. In order to do this the glyphosate must pass through an
oil layer, a water layer and another oil layer. Then glyphosate must travel through the plant in a water system. Water and oil
do not mix therefore glyphosate must change from being able to pass through water then change to a form that can pass
through oil and change back to a form that it can pass through water.
The active ingredient, glyphosate is polar with a negative (-) charge.
Glyphosate is formulated as a weak acid. It joins with positive hydrogens. When they join together the two of them form a
particle that has no charge. The particle is neutral. Neutral particles without a charge can pass through oil dissolving
materials.
The negative active ingredient, glyphosate, can join together with positive surfactants and become neutral. The surfactant
when joined together with glyphosate will cause a droplet of water containing the surfactant and glyphosate to spread out
on the leaf surface increasing the area that can absorb the glyphosate into the leaf. The surfactant used in the formulation
will also make glyphosate mix better and be easier to apply.
When more molecules or particles are next to an area with less of the same particles, the particles will move freely to the
area with the lesser number. This is referred to as a concentration gradient. This occurs until the number of molecules in
both areas are the same or equal. This is how neutral glyphosate moves through the wax or oil surface of the weed’s leaves.
The glyphosate moves through the weed’s cuticle. Weed’s have a cuticle on their aerial surfaces. The cuticle has three
layers. The outside layer is wax, an oil material. The mid layer of the cuticle has both water soluble pectin strands and wax.
The inside layer next to the cell wall contains water. The cell wall of a weed cell is made of cellulose and other materials
that allow water to pass freely through it. The cell wall supports the weed which is unlike animals who get their support
from their skeletons. Animals do not have cell walls.
Once the neutral glyphosate joined with its surfactant passes through the waxy outer layer of the cuticle, it enters the
water soluble pectin strands and then into the water and through the cell wall. Once the neutral glyphosate enters the water
area of the weed the two particles, glyphosate and its surfactant divide. Glyphosate becomes a negative charged particle
that is soluble in water.
The post emergent systemic herbicides are usually weak acids. 2-4D and Poast are weak acids. The active ingredient is
negative (-). As a weak acid the active ingredient, glyphosate, with its negative charge is weakly bound to a positive(+)
charged hydrogen ion. In basic water solutions that have low amounts of hydrogen ions the weak acids like Round Up
donate hydrogen ions to the solution. This changes the glyphosate to a negative (-) charged particle that is easily
transported in the basic solutions that have low numbers of hydrogen ions. In acid solutions with high amounts of
hydrogen ions the weak acid picks up hydrogen ions and becomes a neutral particle without a charge. This neutral particle,
a weak acid containing joined glyphosate and hydrogen ions, can pass through oil barriers.
On the glyphosates journey through the wax oily surface of the cuticle it was bound to the surfactant as a neutral particle
that freely passed into the water in the pectin strands. Once in the basic water solution the glyphosate splits with the
surfactant becoming a negative charged glyphosate particle. This negative glyphosate stayed in the water and travels with
the water through the cell wall. Once past the cell wall the negative charged glyphosate was stopped by the cell membrane
that is an oil structure and won’t allow charged glyphosate to pass through.
Inside the cell membrane the cytoplasm solution is basic and has to keep a low amount hydrogen ions present to remain
basic with a pH above 7. Inside the living cell hydrogen ions are produced by the activity of the living cell processes.
Special protein pumps keep the number of hydrogen ions low in the basic cytoplasm solution by pumping the hydrogen
ions out of the cell through the cell membrane. The special protein pumping causes a build up of hydrogen ions in the water
solution just outside the cell membrane.
The negative charged glyphosate in the water outside the cell membrane hooks up with these hydrogen ions that have been
pumped through the cell membrane. Now the glyphosate as a weak acid is neutral and can freely pass through the cell
membrane. Once inside the cell membrane the hydrogen ion (+) and glyphosate (-) split up in the basic water soluble
cytoplasm of the living cell. The cell walls have openings or holes through which the weed cell material inside its membrane
is connected to the rest of the living cells of the weed. The living cells of the entire growing weed share the same cell
membrane. Inside the living cell membrane the glyphosate can travel throughout the weed in the living fluids inside the cell
membrane.
A living weed cell is similar to a rubber balloon containing fluid and various materials inside a building. The balloon skin
can fill many rooms spreading from room to room through openings in the walls dividing the rooms. The particles and fluid
in the balloon can travel from room to room through these openings in the wall by staying inside the membrane of the
balloon.
The weed’s phloem is a group of these living cells connected together end to end inside cell walls forming phloem tubes.
The phloem vascular system is used by the weed to move sugars from where they are produced to plant locations where
these sugars are used by the plant.
The sugar produced through the process of photosynthesis in the leaves enters the phloem from the adjoining sugar
producing cells along with water. In the confined phloem tube inside the cell walls and membrane the mixture of water and
sugar swells up. This swelling causes pressure build-up. The pressure caused by combining sugar and water pushes the
sugar and water to the place where the sugar is used by the weed; “ the sink“. The place in the weed producing the sugar is
called the “source”. Sources are mature leaves where photosynthesis makes sugar. The area where the sugar is being used
is called the “sink”. The “sinks” can be new shoots, new bud formations, fruiting areas, new root growth or storage areas
in the weed. When the sugar reaches a “sink” like a growing shoot, the sugar or food is used in the growth processes of
the shoot. Then the water is diffused to the other areas of the plant where it is needed. Once glyphosate gets inside a cell
membrane it moves to the phloem vascular system then moves or “hitchikes” with the sugar to the target enzyme. In order
that glyphosate keeps moving throughout the weed’s vascular system the weed has to keep growing as vigorously as
possible.
Glyphosate has an advantage over other systemic herbicides. Glyphosate works better when applied at lower volumes of
water. Good coverage with high volumes of water is one major requirement for control with most herbicides. However
tests using lower volume and nozzles that reduce the formation of small droplets increased the activity of glylphosate in
88% of the tests. Large droplets and reduced spray volume usually reduces the activity of other systemic herbicides.
Glyphosate when applied to larger weeds without increasing the volume of water performed better than other post
emergence herbicides. Glyphosate stays active longer and moves to the growing points of the weed faster than other leaf
applied herbicides.
One reason given for glyphosate’s good performance in lower volumes of water is that water contains materials like
calcium and magnesium. These materials when in the salt stage are positive charged calcium and magnesium ions. They
will tie up the negative charged glyphosate (-). This is referred to as “hard water”. The tied up calcium glyphosate and
magnesium glyphsate will settle out as solids in the bottom of the spray tank or stay on the leaf and become useless. The
higher water volume exposes glyphosate to more tie up. The use of lower volumes reduces the chances of glyphosate tie-
up. Each droplet contains more weed killing free glyphosate in low water volume applications.
The label has rates of sulfate of ammonium fertilizer that can be added to known hard water to prevent losses of the
herbicide due to tie-up. The calcium and magnesium will take the place of the glyphosate and tie-up with the sulfate in
added ammonium sulfate. They become the solids calcium sulfate and magnesium sulfate. Ammonium sulfate when
dissolved in water releases hydrogen ions that forms neutral forms of the weak acid, glyphosate, and aids in the penetration
of oil or waxy like barriers.
For twenty years glyphosate weed resistance was of no great problem. Other herbicides developed resistant problems in a
much shorter period of time. The weeds that developed resistance to glyphosate did this in a number of ways. Weeds like
the resistant horseweed produced more of the target enzyme then the glyphosate could destroy. This allowed the weed to
carry on protein production and continue to thrive.
Another method that resistant weeds used was the interception of glyphosate before it entered the membrane of the living
cell where it is moved in the living phloem throughout the plant. Some theorized that the intercepted glyphosate moved
inside the walls of the xylem vascular system where water moves only up to the leaves. It is then absorbed into the living
cell mebranes of the leaves where it ties up with the enzyme. The roots of the weed aren’t affected and they send out new
shoots keeping the weed alive.
The third form of glyphosate resistance was when plants, in this case marestail weeds, were sprayed with glyphosate.
The growing points yellowed, but didn’t die. The bottom of the plant generated new branches and the weed kept growing.
This form of resistance overcomes the effects of glyphosate by diluting the herbicide with excessive branching.
The number of glyphosate resistant weeds is still limited, but resistant weeds are increasing. Application according to label
instructions is required to reduce the number of new weeds that are resistant to glyphosate. The use of alternatives weed
control methods without complete dependence on glyphosate will delay a buildup of the number of resistant weeds in citrus
orchards that you are responsible for.
Glyphosate has several advantages:
It is effective in low volumes of water. The lowest water volume label rate can often be used if drift is not a problem.
It is rarely detoxified by most of the weeds.
It can be applied through nozzles that reduce the size of the droplets. This reduces drift and allows less water to be applied.
It travels faster through the weed to the growing points. This allows the herbicide to kill the weed before the weed
stops functioning allowing more target contact of more of the weed.
It is tightly held by soil particles thus reducing leaching to the ground water.
Many formulations contain their own adjuvant.
It travels to the growing points in the weed’s roots. This makes glyphosate ideal for tough perennial weed control.
During cool or cloudy weather the glyphosate treated weed will be controlled even though the symptoms may take longer to
appear.
There are some control situations that should be avoided with glyphosate.
It isn’t a soil applied herbicide. In dirty water containing soil or organic matter glyphosate is tied-up becoming ineffective.
When heavy dew is present on the weeds glyphosate will wash off.
Glyphosate is a non-selective herbicide. It will injure non-resistant crops it contacts unlike Poast, Fusilade and 24-D.
On orchards with weeds in various growing conditions and sizes more applications may be needed.
In order for glyphosate to move actively with sugars to vital growing points in the weed apply during daylight hours when
photosynthesis is occurring.
Weeds that are stressed from heat, drought and pest damage will not be active enough
to carry the glyphosate to the growing points where control takes place .
The use of trade names in this course is solely for the purpose of providing specific information. It is not a guarantee or
warranty of the products named, and does not signify that they are approved to the exclusion of others of suitable
composition. Use pesticides safely. Read and follow directions on the manufacturer’s label.
Acknowledgements:
www.ag.ohio-state.edu/%7Eextension/index.php"
www.ag.ohio-st"ate.edu/%7Eextension/about/ index.php"
www.weeds.iastate.edu/mgmt/2001/cuticle2.JPG""http://www.weeds.iastate.edu/mgmt/2001/cuticle2.JPG"
/www.weeds.iastate.edu/mgmt/2006/glyphosatetrans.shtml
www.weeds.iastate.edu/mgmt/2007/glysurvival.
www.weeds.iastate.edu/mgmt/2003/nozzlestudy.shtml
Kimball, John W. “Kimball’s Biology Pages”
Ask citrus growers in California or Arizona other than an organic grower “What herbicide do you use?” and the answer
will probably be Round Up. The use of glyphosate (Round Up) for citrus weed control is world wide. Herbicide use reports
in Arizona show glyphosate use in citrus at 14 to 1 over other herbicides. There are several reasons for this and the main
reason is that glyphosate works in more weed control situations than other methods.
Glyphosate is a substituted amino acid formulated to be accepted by weeds as a herbicide. The glyphosate compound is
allowed by the weed to bind very strongly with a vital enzyme. This enzyme is needed by the weed to produce proteins that
are responsible for the formation of nearly 35% of the dry weight of weeds. Once the glyphosate compound binds with this
enzyme in the weed the enzyme doesn’t function. The loss of the enzyme’s activities usually results in the death of the
weed. Animals do not have this particular enzyme that glyphosate can bind with in their system. This glyphosate substituted
amino acid is specific for binding with this specific enzyme in weeds.
After the researchers found this compound that would bind with and stop the enzyme from functioning they had to find a
way to get the glyphosate to the enzyme. This particular enzyme is located in the growing systems of the weed. These
parts include new shoots, new root tips, young buds and meristem cell areas of growth.
In the weed’s body food or sugar is produced in one location and the energy in the sugar or food is used or stored in
growth areas and storage areas. There is a name for these growth and storage locations in the weed. Growth and storage
locations are called “sinks“. The storage areas “sinks” where water soluble sugars are changed to water insoluble starch
that can be stored include the weed’s roots.
When trying to kill weeds in the past, contact weed killers like petroleum oils were used. This contact weed control
method only killed young seedlings and other annual weeds that don’t have the type of roots that can support the growth of
new shoots. Disking and other forms of cultivation give the same results as contact herbicides. In some cases repeated
applications of contact herbicides or repeated disking and cultivation could kill these roots by cutting off their food supply
and starving them to death.
The weed’s body locations of sugar or food production is where photosynthesis takes place. Photosynthesis combines
sunlight energy with carbon dioxide and water to produce sugars and oxygen. This food production takes place in
chlorophyll containing cells. Photosynthesis takes place in most of the mature aerial parts of the weed. These places are
called “sources”. When the sugar reaches a storage area like the roots an enzyme causes the water soluble sugar to form
molecular long chains. The chains of sugar molecules are called starch which is not water soluble. Because of this
insolubility of starch the water diffuses to an area in the plant where it’s needed leaving the starch in the storage or “sink”
When food is needed by the weed in growth areas another enzyme causes the starch’s long chains to separate forming
water soluble sugar. The sugar is water soluble again and this storage area becomes a “source” sending sugars to “sinks“.
Depending on the enzyme, storage areas in weeds can be either a “sink” or a “source“.
Entering the weed and traveling to the target enzyme has to be done with the help of the weed. Glyphosate has to get to its
target using the weed’s translocation system. In order to do this the glyphosate must change its chemical formulation to
take advantage of the weeds system that moves materials around inside the weed. Glyphosate becomes a “hitchiker” in the
weeds vascular transport system.
Glyphosate must first get to the vascular system inside the weed. In order to do this the glyphosate must pass through an
oil layer, a water layer and another oil layer. Then glyphosate must travel through the plant in a water system. Water and oil
do not mix therefore glyphosate must change from being able to pass through water then change to a form that can pass
through oil and change back to a form that it can pass through water.
The active ingredient, glyphosate is polar with a negative (-) charge.
Glyphosate is formulated as a weak acid. It joins with positive hydrogens. When they join together the two of them form a
particle that has no charge. The particle is neutral. Neutral particles without a charge can pass through oil dissolving
materials.
The negative active ingredient, glyphosate, can join together with positive surfactants and become neutral. The surfactant
when joined together with glyphosate will cause a droplet of water containing the surfactant and glyphosate to spread out
on the leaf surface increasing the area that can absorb the glyphosate into the leaf. The surfactant used in the formulation
will also make glyphosate mix better and be easier to apply.
When more molecules or particles are next to an area with less of the same particles, the particles will move freely to the
area with the lesser number. This is referred to as a concentration gradient. This occurs until the number of molecules in
both areas are the same or equal. This is how neutral glyphosate moves through the wax or oil surface of the weed’s leaves.
The glyphosate moves through the weed’s cuticle. Weed’s have a cuticle on their aerial surfaces. The cuticle has three
layers. The outside layer is wax, an oil material. The mid layer of the cuticle has both water soluble pectin strands and wax.
The inside layer next to the cell wall contains water. The cell wall of a weed cell is made of cellulose and other materials
that allow water to pass freely through it. The cell wall supports the weed which is unlike animals who get their support
from their skeletons. Animals do not have cell walls.
Once the neutral glyphosate joined with its surfactant passes through the waxy outer layer of the cuticle, it enters the
water soluble pectin strands and then into the water and through the cell wall. Once the neutral glyphosate enters the water
area of the weed the two particles, glyphosate and its surfactant divide. Glyphosate becomes a negative charged particle
that is soluble in water.
The post emergent systemic herbicides are usually weak acids. 2-4D and Poast are weak acids. The active ingredient is
negative (-). As a weak acid the active ingredient, glyphosate, with its negative charge is weakly bound to a positive(+)
charged hydrogen ion. In basic water solutions that have low amounts of hydrogen ions the weak acids like Round Up
donate hydrogen ions to the solution. This changes the glyphosate to a negative (-) charged particle that is easily
transported in the basic solutions that have low numbers of hydrogen ions. In acid solutions with high amounts of
hydrogen ions the weak acid picks up hydrogen ions and becomes a neutral particle without a charge. This neutral particle,
a weak acid containing joined glyphosate and hydrogen ions, can pass through oil barriers.
On the glyphosates journey through the wax oily surface of the cuticle it was bound to the surfactant as a neutral particle
that freely passed into the water in the pectin strands. Once in the basic water solution the glyphosate splits with the
surfactant becoming a negative charged glyphosate particle. This negative glyphosate stayed in the water and travels with
the water through the cell wall. Once past the cell wall the negative charged glyphosate was stopped by the cell membrane
that is an oil structure and won’t allow charged glyphosate to pass through.
Inside the cell membrane the cytoplasm solution is basic and has to keep a low amount hydrogen ions present to remain
basic with a pH above 7. Inside the living cell hydrogen ions are produced by the activity of the living cell processes.
Special protein pumps keep the number of hydrogen ions low in the basic cytoplasm solution by pumping the hydrogen
ions out of the cell through the cell membrane. The special protein pumping causes a build up of hydrogen ions in the water
solution just outside the cell membrane.
The negative charged glyphosate in the water outside the cell membrane hooks up with these hydrogen ions that have been
pumped through the cell membrane. Now the glyphosate as a weak acid is neutral and can freely pass through the cell
membrane. Once inside the cell membrane the hydrogen ion (+) and glyphosate (-) split up in the basic water soluble
cytoplasm of the living cell. The cell walls have openings or holes through which the weed cell material inside its membrane
is connected to the rest of the living cells of the weed. The living cells of the entire growing weed share the same cell
membrane. Inside the living cell membrane the glyphosate can travel throughout the weed in the living fluids inside the cell
membrane.
A living weed cell is similar to a rubber balloon containing fluid and various materials inside a building. The balloon skin
can fill many rooms spreading from room to room through openings in the walls dividing the rooms. The particles and fluid
in the balloon can travel from room to room through these openings in the wall by staying inside the membrane of the
balloon.
The weed’s phloem is a group of these living cells connected together end to end inside cell walls forming phloem tubes.
The phloem vascular system is used by the weed to move sugars from where they are produced to plant locations where
these sugars are used by the plant.
The sugar produced through the process of photosynthesis in the leaves enters the phloem from the adjoining sugar
producing cells along with water. In the confined phloem tube inside the cell walls and membrane the mixture of water and
sugar swells up. This swelling causes pressure build-up. The pressure caused by combining sugar and water pushes the
sugar and water to the place where the sugar is used by the weed; “ the sink“. The place in the weed producing the sugar is
called the “source”. Sources are mature leaves where photosynthesis makes sugar. The area where the sugar is being used
is called the “sink”. The “sinks” can be new shoots, new bud formations, fruiting areas, new root growth or storage areas
in the weed. When the sugar reaches a “sink” like a growing shoot, the sugar or food is used in the growth processes of
the shoot. Then the water is diffused to the other areas of the plant where it is needed. Once glyphosate gets inside a cell
membrane it moves to the phloem vascular system then moves or “hitchikes” with the sugar to the target enzyme. In order
that glyphosate keeps moving throughout the weed’s vascular system the weed has to keep growing as vigorously as
possible.
Glyphosate has an advantage over other systemic herbicides. Glyphosate works better when applied at lower volumes of
water. Good coverage with high volumes of water is one major requirement for control with most herbicides. However
tests using lower volume and nozzles that reduce the formation of small droplets increased the activity of glylphosate in
88% of the tests. Large droplets and reduced spray volume usually reduces the activity of other systemic herbicides.
Glyphosate when applied to larger weeds without increasing the volume of water performed better than other post
emergence herbicides. Glyphosate stays active longer and moves to the growing points of the weed faster than other leaf
applied herbicides.
One reason given for glyphosate’s good performance in lower volumes of water is that water contains materials like
calcium and magnesium. These materials when in the salt stage are positive charged calcium and magnesium ions. They
will tie up the negative charged glyphosate (-). This is referred to as “hard water”. The tied up calcium glyphosate and
magnesium glyphsate will settle out as solids in the bottom of the spray tank or stay on the leaf and become useless. The
higher water volume exposes glyphosate to more tie up. The use of lower volumes reduces the chances of glyphosate tie-
up. Each droplet contains more weed killing free glyphosate in low water volume applications.
The label has rates of sulfate of ammonium fertilizer that can be added to known hard water to prevent losses of the
herbicide due to tie-up. The calcium and magnesium will take the place of the glyphosate and tie-up with the sulfate in
added ammonium sulfate. They become the solids calcium sulfate and magnesium sulfate. Ammonium sulfate when
dissolved in water releases hydrogen ions that forms neutral forms of the weak acid, glyphosate, and aids in the penetration
of oil or waxy like barriers.
For twenty years glyphosate weed resistance was of no great problem. Other herbicides developed resistant problems in a
much shorter period of time. The weeds that developed resistance to glyphosate did this in a number of ways. Weeds like
the resistant horseweed produced more of the target enzyme then the glyphosate could destroy. This allowed the weed to
carry on protein production and continue to thrive.
Another method that resistant weeds used was the interception of glyphosate before it entered the membrane of the living
cell where it is moved in the living phloem throughout the plant. Some theorized that the intercepted glyphosate moved
inside the walls of the xylem vascular system where water moves only up to the leaves. It is then absorbed into the living
cell mebranes of the leaves where it ties up with the enzyme. The roots of the weed aren’t affected and they send out new
shoots keeping the weed alive.
The third form of glyphosate resistance was when plants, in this case marestail weeds, were sprayed with glyphosate.
The growing points yellowed, but didn’t die. The bottom of the plant generated new branches and the weed kept growing.
This form of resistance overcomes the effects of glyphosate by diluting the herbicide with excessive branching.
The number of glyphosate resistant weeds is still limited, but resistant weeds are increasing. Application according to label
instructions is required to reduce the number of new weeds that are resistant to glyphosate. The use of alternatives weed
control methods without complete dependence on glyphosate will delay a buildup of the number of resistant weeds in citrus
orchards that you are responsible for.
Glyphosate has several advantages:
It is effective in low volumes of water. The lowest water volume label rate can often be used if drift is not a problem.
It is rarely detoxified by most of the weeds.
It can be applied through nozzles that reduce the size of the droplets. This reduces drift and allows less water to be applied.
It travels faster through the weed to the growing points. This allows the herbicide to kill the weed before the weed
stops functioning allowing more target contact of more of the weed.
It is tightly held by soil particles thus reducing leaching to the ground water.
Many formulations contain their own adjuvant.
It travels to the growing points in the weed’s roots. This makes glyphosate ideal for tough perennial weed control.
During cool or cloudy weather the glyphosate treated weed will be controlled even though the symptoms may take longer to
appear.
There are some control situations that should be avoided with glyphosate.
It isn’t a soil applied herbicide. In dirty water containing soil or organic matter glyphosate is tied-up becoming ineffective.
When heavy dew is present on the weeds glyphosate will wash off.
Glyphosate is a non-selective herbicide. It will injure non-resistant crops it contacts unlike Poast, Fusilade and 24-D.
On orchards with weeds in various growing conditions and sizes more applications may be needed.
In order for glyphosate to move actively with sugars to vital growing points in the weed apply during daylight hours when
photosynthesis is occurring.
Weeds that are stressed from heat, drought and pest damage will not be active enough
to carry the glyphosate to the growing points where control takes place .
The use of trade names in this course is solely for the purpose of providing specific information. It is not a guarantee or
warranty of the products named, and does not signify that they are approved to the exclusion of others of suitable
composition. Use pesticides safely. Read and follow directions on the manufacturer’s label.
Acknowledgements:
www.ag.ohio-state.edu/%7Eextension/index.php"
www.ag.ohio-st"ate.edu/%7Eextension/about/ index.php"
www.weeds.iastate.edu/mgmt/2001/cuticle2.JPG""http://www.weeds.iastate.edu/mgmt/2001/cuticle2.JPG"
/www.weeds.iastate.edu/mgmt/2006/glyphosatetrans.shtml
www.weeds.iastate.edu/mgmt/2007/glysurvival.
www.weeds.iastate.edu/mgmt/2003/nozzlestudy.shtml
Kimball, John W. “Kimball’s Biology Pages”