Agricultural

Chemicals
 Agricultural Chemicals
Agricultural chemicals are chemical agents such as
fungicides and pesticides that are used to control crop-harming
organisms (e.g., fungi, nematodes, mites, insects, and rodents)
or viruses. The chemical agents include those manufactured
using the chemical agents as raw materials or ingredients that
are intended to control the diseases and pests. The law also
includes "natural enemies" and "microorganisms" that are used
to control diseases and pests of agricultural and other products,
as the agricultural chemicals.
Agricultural Chemicals
Agents that simultaneously control harmful insect
Pesticides pest and diseases that damage field crops.

Agents for controlling dieseases that damage field

Fungicides crops

Herbicides Agents for controlling weeds.

Plant Growth Agents to promote or inhibit the growth of field

Hormone crops
Why are Agricultural Chemicals
used?
People have long endeavored to protect field
crops from disease, pests and weeds. These methods
include breeding varieties resistant to pests and
diseases, cultural control of diseases and pests by
plowing and removing crop debris after harvest,
physical pest control such as soil disinfection using
solar heating, and biotic control using natural enemies
such as spiders. In addition, agricultural chemicals are
used because they produce certain effects with less
effort.
 Products of Microbial Process for
Agricultural Chemicals

• Pesticides
• Herbicides
• Insectides
• Plant growth hormones
 Pesticides
Pesticides are any substances intended for preventing,
destroying, or controlling any pest, including vectors of
human or animal disease, unwanted species of plants or
animals, causing harm during or otherwise interfering with
the production, processing, storage, transport, or marketing
of food, agricultural commodities, wood and wood products
or animal feedstuffs, or substances that may be administered
to animals for the control of insects, arachnids, or other pests
in or on their bodies.
 In general, a pesticide is a chemical or
biological agent that deters, incapacitates, kills, or
otherwise discourages pests. Target pests can include
insects, plant pathogens, weeds, molluscs, birds,
mammals, fish, nematodes (roundworms), and
microbes that destroy property, cause nuisance, or
spread disease, or are disease vectors. Along with
these benefits, pesticides also have drawbacks, such as
potential toxicity to humans and other species.
 Application
Pesticides are used to control organisms that are
considered to be harmful. For example, they are used
to kill mosquitoes that can transmit potentially deadly
diseases like West Nile virus, yellow fever, and
malaria. They can also kill bees, wasps or ants that can
cause allergic reactions. Pesticides can protect animals
from illnesses that can be caused by parasites such as
fleas.
Fungicides
Fungicides are pesticides that kill or prevent
the growth of fungi and their spores. They can be
used to control fungi that damage plants, including
rusts, mildews and blights. They might also be used
to control mold and mildew in other settings.
Fungicides work in a variety of ways, but most of
them damage fungal cell membranes or interfere with
energy production within fungal cells.
 A fungicide is any substance, preparation, or
organism intended for destroying or controlling any
fungal species during production, storage, or
distribution of an agricultural commodity or food, in
ornamental plants, or in situations endangering the
health of animals or humans. Numerous organic
chemicals, as well as some inorganic ones, are
formulated for use as fungicides in agriculture and
food storage. Fungicides help to increase efficiency
of production, by preventing or reducing damage to
the growing crop or stored commodity, and to
improve the quality of the product, by preventing
rotting and a damaged appearance.
Types of Fungicides
• Preventive fungicides–These are substances that
prevent fungal infections from occurring in a plant.
They include compounds such as sulfur,
dichlorocarbamates, organometallics, pthalimides,
and benzimides.
• Curative fungicides–These are substances that
move to the place where the infection has occurred
and prevent further development of the pathogen.
They include compounds such as acetimides,
dicarboxymides, sterol inhibitors, and many others.
Importance of Fungicides
Diseases are a common occurrence on plants, often
having a significant economic impact on yield and quality,
thus managing diseases is an essential component of
production for most crops. Broadly, there are three main
reasons fungicides are used:
(a) To control a disease during the establishment and
development of a crop.
(b) To increase productivity of a crop and to reduce
blemishes. Diseased food crops may produce less because
their leaves, which are needed for photosynthesis, are affected
by the disease
(c) To improve the storage life and quality of harvested plants
and produce.
Herbicides
An agent, usually chemical, for killing
or inhibiting the growth of unwanted plants, such as
residential or agricultural weeds and invasive species.
A great advantage of chemical herbicides over
mechanical weed control is the ease of application,
which often saves on the cost of labour. Most
herbicides are considered nontoxic to animals and
humans, but they can cause substantial mortality of
nontarget plants and the insects that depend on them,
especially when applied aerially.
 Selective herbicides control specific weed
species, while leaving the desired crop relatively
unharmed, while non-selective herbicides
(sometimes called total weedkillers in commercial
products) can be used to clear waste ground,
industrial and construction sites, railways and railway
embankments as they kill all plant material with
which they come into contact.
Classification of Herbicides

Herbecides are classified/grouped in

various ways, according to the activity,
timing of application and method of
application.
 Timing of Application
Preplant: Preplant herbicides are nonselective
herbicides applied to soil before planting. Some
preplant herbicides may be mechanically incorporated
into the soil. The objective for incorporation is to
prevent dissipation through photodecomposition and/or
volatility. The herbicides kill weeds as they grow
through the herbicide treated zone. Agricultural crops
grown in soil treated with a preplant herbicide include
tomatoes, corn, soybeans and strawberries. Soil
fumigants like metam-sodium and dazomet are in use as
preplant herbicides.
Preemergence: Preemergence herbicides are applied
before the weed seedlings emerge through the soil
surface. Herbicides do not prevent weeds from
germinating but they kill weeds as they grow through
the herbicide treated zone by affecting the cell
division in the emerging seedling. Dithopyr and
pendimethalin are preemergence herbicides. Weeds
that have already emerged before application or
activation are not affected by pre-herbicides as their
primary growing point escapes the treatment.
Postemergence: These herbicides are applied after
weed seedlings have emerged through the soil
surface. They can be foliar or root absorbed, selective
or nonselective, contact or systemic. Application of
these herbicides is avoided during rain because the
problem of being washed off to the soil makes it
ineffective. 2,4-D is a selective, systemic, foliar
absorbed postemergence herbicide.
Method of application
Soil applied: Herbicides applied to the soil are
usually taken up by the root or shoot of the emerging
seedlings and are used as preplant or preemergence
treatment. Several factors influence the effectiveness
of soil-applied herbicides. Weeds absorb herbicides
by both passive and active mechanism. Herbicide
adsorption to soil colloids or organic matter often
reduces its amount available for weed absorption.
Positioning of herbicide in correct layer of soil is very
important, which can be achieved mechanically and
by rainfall.
Herbicides on the soil surface are subjected to several
processes that reduce their availability. Volatility and
photolysis are two common processes that reduce the
availability of herbicides. Many soil applied
herbicides are absorbed through plant shoots while
they are still underground leading to their death or
injury. EPTC and trifluralin are soil applied
herbicides.
Foliar applied: These are applied to portion of the
plant above the ground and are absorbed by exposed
tissues. These are generally postemergence herbicides
and can either be translocated (systemic) throughout
the plant or remain at specific site (contact). External
barriers of plants like cuticle, waxes, cell wall etc.
affect herbicide absorption and action. Glyphosate,
2,4-D and dicamba are foliar applied herbicide.
Application
Most herbicides are applied as water-based
sprays using ground equipment. Ground equipment
varies in design, but large areas can be sprayed using
self-propelled sprayers equipped with long booms, of
60 to 120 feet (18 to 37 m) with spray nozzles spaced
every 20–30 inches (510–760 mm) apart. Towed,
handheld, and even horse-drawn sprayers are also
used. On large areas, herbicides may also at times be
applied aerially using helicopters or airplanes, or
through irrigation systems (known as chemigation).
 Weed-wiping may also be used, where a
wick wetted with herbicide is suspended from a
boom and dragged or rolled across the tops of
the taller weed plants. This allows treatment of
taller grassland weeds by direct contact without
affecting related but desirable shorter plants in
the grassland sward beneath. The method has
the benefit of avoiding spray drift. In Wales, a
scheme offering free weed-wiper hire was
launched in 2015 in an effort to reduce the
levels of MCPA in water courses.
Uses
Herbicides can be used to clear roadside
weeds, trees, and brush. They can also kill invasive
weeds that may cause environmental damage.
Herbicides are commonly applied in ponds and lakes
to control algae and plants such as water grasses that
can interfere with activities like swimming and
fishing and cause the water to look or smell
unpleasant. Uncontrolled pests such as termites and
mold can damage structures such as houses.
List of Common Herbicides
• 2,4-D is a broadleaf herbicide in the phenoxy group
used in turf and no-till field crop production. Now,
it is mainly used in a blend with other herbicides to
allow lower rates of herbicides to be used; it is the
most widely used herbicide in the world, and third
most commonly used in the United States. It is an
example of synthetic auxin (plant hormone).
• Aminopyralid is a broadleaf herbicide in the
pyridine group, used to control weeds on grassland,
such as docks, thistles and nettles. It is notorious for
its ability to persist in compost.
• Atrazine, a triazine herbicide, is used in corn and
sorghum for control of broadleaf weeds and grasses.
Still used because of its low cost and because it
works well on a broad spectrum of weeds common
in the US corn belt, atrazine is commonly used with
other herbicides to reduce the overall rate of
atrazine and to lower the potential for groundwater
contamination; it is a photosystem II inhibitor.
• Glyphosate, a systemic nonselective herbicide, is
used in no-till burndown and for weed control in
crops genetically modified to resist its effects. It is
an example of an EPSPs inhibitor.

• Linuron is a nonselective herbicide used in the

control of grasses and broadleaf weeds. It works by
inhibiting photosynthesis
 Plant Growth Hormones
Plant hormones (also known as phytohormones)
are signal molecules produced within plants, that occur
in extremely low concentrations. Plant hormones
control all aspects of growth and development, from
embryogenesis, the regulation of organ size, pathogen
defense, stress tolerance and through to reproductive
development. Unlike in animals (in which hormone
production is restricted to specialized glands) each
plant cell is capable of producing hormones.The term
'phytohormone' was coined by Went and Thimann and
used in the title of their book in 1937.
 Phytohormones are found across the plant
kingdom, and even in algae, where they have similar
functions to those seen in higher plants.Some
phytohormones also occur in microorganisms, such as
unicellular fungi and bacteria, however in these cases
they do not play a hormonal role and can better be
regarded as secondary metabolites.
Classification of Plant Hormones
• Plant Growth Promoters – They promote cell
division, cell enlargement, flowering, fruiting and
seed formation. Examples are auxins, gibberellins
and cytokinins.
• Plant Growth Inhibitors – These chemicals inhibit
growth and promote dormancy and abscission in
plants. An example is an abscisic acid.
 Types of Plant Growth Hormones
• Auxins
An auxin, indole‐3‐acetic acid (IAA), was the first
plant hormone identified. It is manufactured primarily in the
shoot tips (in leaf primordia and young leaves), in embryos,
and in parts of developing flowers and seeds. Its transport
from cell to cell through the parenchyma surrounding the
vascular tissues requires the expenditure of ATP energy. IAA
moves in one direction only—that is, the movement is polar
and, in this case, downward. Such downward movement in
shoots is said to be basipetal movement, and in roots it is
acropetal.
 Auxins alone or in combination with other hormones
are responsible for many aspects of plant growth. IAA in
particular:
• Promotes growth of vascular tissue in healing of
wounds.
• Activates a gene required for making a protein necessary
for growth and other genes for the synthesis of wall
materials made and secreted by dictyosomes.
• Promotes initiation and growth of adventitious roots in
cuttings.
• Promotes the growth of many fruits (from auxin
produced by the developing seeds).
• Cytokinins
Named because of their discovered role in cell division
(cytokinesis), the cytokinins have a molecular structure similar
to adenine. Cytokinins are found in sites of active cell division
in plants—for example, in root tips, seeds, fruits, and leaves.
They are transported in the xylem and work in the presence of
auxin to promote cell division. Differing cytokinin:auxin ratios
change the nature of organogenesis. If kinetin is high and
auxin low, shoots are formed; if kinetin is low and auxin high,
roots are formed. Cytokinins are also involved in repair, if a
plant is wounded, it can fix itself with the help of cytokinins
and auxins.
• Ethylene
Ethylene is a simple gaseous hydrocarbon produced from
an amino acid and appears in most plant tissues in large amounts
when they are stressed. It diffuses from its site of origin into the
air and affects surrounding plants as well. Large amounts
ordinarily are produced by roots, senescing flowers, ripening
fruits, and the apical meristem of shoots. Auxin increases
ethylene production, as does ethylene itself—small amounts of
ethylene initiate copious production of still more. Ethylene
stimulates the ripening of fruit and initiates abscission of fruits
and leaves. Ethylene can be produced in almost any part of a
plant, and can diffuse through the plant’s tissue, outside the
plant, and travel through the air to affect a totally different plant.
 Production of Pesticides
In pesticide manufacturing, an active
ingredient is first synthesized in a chemical factory.
Next, a formulator mixes the active ingredient with a
carrier. Liquid pesticides are packaged in 200-liter
drums for large-scale operations or 20-liter jugs for
small-scale operations, while dry formulations can
be packaged in 5 to 10 kilogram plastic or plastic-
lined bags.
 Raw Materials
Active ingredients were once distilled from natural
substances; now they are largely synthesized in a laboratory.
Almost all are hydrocarbons derived from petroleum. Most
pesticides contain other elements, the type and number of which
depend on the pesticide desired. Chlorine, oxygen, sulfur,
phosphorus, nitrogen, and bromine are most common. Inert
ingredients can be many substances, dependent on the type of
pesticide. Liquid pesticides have traditionally used kerosene or
some other petroleum distillate as a carrier, though water has
recently begun to replace kerosene.
Raw Materials
Emulsifiers (such as soap) are also added to
distribute the active ingredient evenly throughout the
solvent. A powder or dust pesticide will typically
contain vegetable matter such as ground up nut shells
or corn cobs, clays such as diatomite or attapulgite, or
powdered minerals such as talc or calcium carbonate
as a base.
The Manufacturing Process
Manufacturing a pesticide involves at least
three separate activities. The active ingredient is first
synthesized in a chemical factory, then formulated in
the same place or sent to a formulator, who prepares
the liquid or powder form. The pesticide is then sent
to the farmer or other certified applicator, who dilutes
it before applying it to the fields.
Synthesizing the pesticide

When a new pesticide is first developed, it is

manufactured on a small scale in a laboratory. If the substance
proves viable, production begins in the factory. Batch or
continuous manufacturing insures a high volume, perhaps as
much as 500 kilograms per cycle. Synthesizing a pesticide is a
complex chemical procedure that requires trained chemists and
a large, sophisticated laboratory.
 The basic procedure entails altering an organic molecule
to form a pesticide. This may involve any of a number of
specific reagents and catalysts and often must take place in a
controlled climate (within a certain temperature range, for
example). Once synthesized, the active ingredient is packaged
and sent to a formulator. Liquid insecticides can be shipped in
tank trucks or 200-liter drums. Transport of the active ingredient
follows all regulations for hazardous materials transportation.
 Formulating the Pesticide
A formulator accepts the active ingredient, measures out
the proper amount, mixes it with carrier if it is to be a liquid
pesticide or with inert powders or dry fertilizers if it is to be a
dust pesticide, then bottles or packages it. Liquid pesticides are
packaged in 200-liter drums if a large-scale farmer is the
anticipated customer or 20-liter jugs for small-scale operations.
Dry formulations can be packaged in 5 to 10 kilogram plastic or
plastic-lined bags. An emulsified formulation is usually
concentrated to render transport easier (the active ingredient
typically makes up 50 percent of the emulsified concentrate),
but granulated and dry pesticides are ready to use.
Diluting the Pesticide

The Pesticide might be stored a short time before

it is requested. When it is ready for transport, the
estimated necessary amount is sent to the farmer, who
dilutes the emulsified concentrate to create the amount
of pesticide desired. In most instances, the final
product consists of only .5 to 1 percent of the original
active ingredient. The pesticide is now ready to be
applied.
 Applying the Pesticide
There are several ways to apply a pesticide. The
method with which Americans are most familiar is crop
dusting, though its use is generally limited to large, flat
areas. A plane loaded with 2000-liter (or larger) tanks
flies over a field and sprays out the pesticide from
booms. Booms are long, horizontal rods from which
several sprinklers spray down. Another method is to
attach the tanks and booms to a tractor and spray closer
to the ground.
 For small farmers, the most economical method
of spraying is to use one or more workers with hand-
held sprayers attached to small tanks. A hand pump can
be carried on the shoulder; its tank capacity is only
about 3 to 12 liters. Small tanks with a capacity of
around 200 liters are also used. The pesticides are
applied with a hand gun. A rough estimate of the
amount applied is 150 to 300 liters per hectare.