Introduction Mode of action: Primary and Secondary Soil applied herbicides and factors affecting them Foliar applied herbicides and factors affecting them Plant leaf cuticle and its structure Herbicide translocation in plant: Symplast and Apoplast

1. CREDIT SEMINAR
TOPIC: MOVEMENT OF HERBICIDE IN
PLANTS AND SOIL
Presented by:
Adit Singla
Roll No. 21-M-AGRI-017
M.Sc. (Ag.) Agronomy
Supervised by:
Dr. S.P. Bainade
Assistant Professor
Department of Agriculture
SAST, RIMT University

2. INTRODUCTION
To produce the ultimate effect, a herbicide need to
move from its site of application (e.g. soil, leave or shoot)
to the site of action, which is normally inside the plant.
Once a herbicide enter into plant and reaches to a
specific site in plant cells or organelles, it affects a single or
in some cases multiple biochemical processes depending of
herbicide.

3.  MOVEMENT OF HERBICIDE
 Movement of herbicide is the process of penetration of
herbicide into the plant tissue.
 Herbicide are applied either to the soil or plant foliage .

4. Mode of action of herbicide refers to the entire chain of
event occurring from its first time of application or contact to its
ultimate effect at the site of action, which could be death of a
plant.
 MODE OF ACTION
 PRIMARY SITE OF ACTION
The site inside the plant system, which is affected first at the
lowest rate of application of a herbicide, is called “the primary
site of action” of that herbicide.
Photosynthesis may be the primary site of action of all triazines,
triazinones, phenylureas and uracils etc

5.  SECONDARY SITE OF ACTION
The site, which also gets affected later in addition to or in
conjunction with the primary site of action is called “the
secondary site of action”.
For example: Respiration, cell division might be the secondary
site of action of all photosynthesis inhibitor herbicide like
triazines, phenylureas and uracils. If photosynthesis is inhibited,
respiration and cell division are likely to be affected due to
reduced supply of sugar in plant.

6.  SOILAPPLIED HERBICIDES
 Herbicide applied to the soil either at pre-planting or pre-
emergence are usually taken up by the root or shoot of the
emerging seedling.
 Water, salt and water soluble herbicide are taken up by root hair
and cortex cell of this primary absorbing region.
 The xylem in the absorbing region is sufficiently differentiated
to be functional and the endodermis, a single layer of closely
packed cell, is not sufficiently lignified to prevent penetration by
solute.

7.  From root hair and cortex, the molecules migrate via the Symplast
into the stele where they leak from the transpiration stream
 They are absorbed by both passive and active mechanisms.
 The passive entrance is primarily along the absorbed water and
herbicide move with the water throughout the plant in the apoplast
system including the xylem.
 Active absorption requires energy and the herbicide enter into the
protoplast and move via the symplast system.
Roots, shoots, and seed are the major sites of uptake of the soil-
applied herbicides.

8.  FACTORS AFFECTING AVAILABILITY OF SOIL-APPLIED
HERBICIDE:
1. Adsorption: Adsorption is holding up of herbicide molecules, ions on the
surface of soil colloids by physicochemical attraction. This leads to the less
availability of herbicide in the soil solution and in tern less uptake by plant.
2. Vaporization: Vaporization leads to less of herbicide activity on account of
its less retention on the plant surface.
3. Photodecomposition: Decomposition of some herbicides takes place in
presence of light and this may lead to less availability of herbicide to plants.
4. Leaching: Leaching of herbicide through soil profiles depends on the
solubility of herbicide, amount of water, soil texture and the adsorptive
capacity of soil.

9. 5. Chemical decomposition: Certain herbicide may undergo
chemical modification or breakdown in soil, which may leads to
their unavailability or less availability to plant
6. Microbial decomposition: Generally warm and moist condition
favor microbial activity and hence the breakdown of herbicide.
Some herbicide persist only for a short while, while others for
more then one year
7. Soil moisture: Moisture helps incorporation of some herbicide
with low solubility and increases the availability for absorption by
root from soil solution.
8. Run off / Wash off: Heavy rain and irrigation may cause off loss
of treated herbicide.

10.  When a herbicide is applied at post-emergence, the spray is usually
directed at the plant, most of the chemical reaching the foliage which
then absorbs the herbicide molecules.
 FOLIAR PENETRATION
 Effect of a herbicide depends upon its ability to penetrate the cuticle
which is a part of the apoplast, and the plasmalemma which covers all
surface of the symplast including plasmodesmata to enter the symplast.
 Foliage applied herbicide may exist in poler from or non-poler from.
 Foliage applied herbicides enter the living cells either by a lipoidal
route or aqueous route or both.
 FOLIAGE APPLIED HERBICIDES

11.  FACTORS AFFECTING AVAILABILITY OF FOLIAGE-
APPLIED HERBICIDE
1. Plant structure: If target plant (weed) are shorter in height
than other plant (crop), greater amount of herbicide will be
intercepted by the taller plant
2. Plant morphology: Plant canopy surface area, nature,
structure and angle of leave, location of growing points, age of
plant particularly in reference to root growth and kind of
steam, e.g. hairy stem, ridged stem etc. affect absorption of
herbicide by plant.
3. Relative humidity: The lower leaf surface is usually more
permeable to herbicide. Herbicide can enter through stomata or
through cuticle. If the humidity is higher, spray solution will
evaporate more slowly, and there will be more opportunity
time for droplets to penetrate the leaves.

12. 4. Vaporization: Vaporization leads to less of
herbicide activity on account of its less retention on
the plant surface.
5. Run off / Wash off: Rain, irrigation, heavy dew, or
a very high spray volume may cause run off or wash
off of treated herbicide.
.

13.  PLANT LEAF CUTICLE
 The herbicide has to pass through a wax layer called cuticle
which protects the inner cells. The cuticle is a thin, continuous,
noncellular lipoidal membrane covering the plant surface.
 It covers the guard, mesophyll, and epidermal cell adjoining the
stomatal chamber and intercellular air spaces in leaves. The
cuticle is made up of four different substances;
Cutin, cutin wax, pectin and cellulose.

14. STRUCTURE OF CUTICLE

15.  HERBICIDE TRANSLOCATION IN PLANTS
A herbicide enters in to a plants through leaves, stems, roots or seed and
reaches to a specific location to suppress some physiological function. This
movement is called translocation.
1. Symplast and symplastic movement: Symplastic movement is a
“source to sink” translocation. Herbicide move trough phloem with
sugars produced during photosynthesis and get accumulated where
sugars and photosynthates (carbon) are being used or stored. In plant,
“sinks” are the site where sugars translocation from the “source” is
where sugar is produced (stroud, 1989).
2. Apoplast and apoplastic movement: In apoplastic movement the
herbicide are primarily absorbed by root and move through xylem in
plants and translocated along with water or mineral nutrient ions and
therefore, the movement may or may not require metabolic energy.

16. 3. Symplast and Apoplast together: Symplast and apoplast
together are involved in the translocation of some herbicides
(example: isoproturon, glyphosate, 2,4-D, atrazine) in plants,
although Symplast for foliage-applied herbicides and apoplast
for soil-applied herbicides from the usual basis of herbicide
movement in plants.
4. No or limited mobility in treated plant: They are mainly
contact herbicide with limited or no mobility plant.
Example: propanil, paraquat and diquat.

17.  HERBICIDE TRANSLOCATION IN PLANTS

18. Contact
Absorption
Movement
Site of Action
HERBICIDE MODE OF ACTION
Toxicity

19. Foliar Contact
(Gramoxone)
Root Contact
(Treflan)
Phloem
(Roundup)
Xylem
(Spike)
Xylem and
Phloem
(Banvel, Tordon)

20. CONCLUSION
1. Movement of herbicide is the process of
penetration of herbicide into the plant tissue.
2. A herbicide enters in to a plants through leaves,
stems, roots or seed and reaches to a specific
location to suppress some physiological function.
3. Symplastic movement is a “source to sink”
translocation.
4. In apoplastic movement the herbicide are primarily
absorbed by root and move through xylem in
plants and translocated along with water or
mineral nutrient ions.