Agrochemicals Word
Agrochemicals Word
Agrochemicals Word
A Brief History
Even before 2000 BC, humans have used pesticides to protect their crops. The
first known pesticide was the elemental sulphur dust used by ancient Sumerians
around 4,500 years ago in ancient Mesopotamia. Rigveda, about 4,000 years old,
refers to the use of poisonous plants to control pests. By the time of the
15th century, toxic chemicals such as arsenic, mercury and lead were useful in
destroying the pests in crops. Nicotine sulphate was derived from tobacco leaves
in the 17th century for use as an insecticide. The 19th century saw the introduction
of two more natural pesticides, pyrethrum, derived from chrysanthemums, and
rotenone, derived from the roots of tropical vegetables. Until the 1950s, pesticides
based on arsenic were dominant.
Paul Müller found that DDT was a highly effective insecticide. Until 1975
organochlorines such as DDT were dominant, but by the year of 1975
organophosphates and carbamate replaced DDT in the US. However, 20 years
later, because of the biological consequences and human safety concerns, almost
86 counties declared the banning of DDT. Since then, pyrethrin compounds have
become the dominant insecticide in the industry. Herbicides became popular in the
early 1960s, then came “triazine and other similar nitrogen-based compounds,
carboxylic acids including glyphosate and 2,4-dichlorophenoxyacetic acid”.
Definitions of Pesticides
The Food and Agriculture Organization (FAO) has defined pesticide as:
“any substance or mixture of 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”.
Types of Pesticides
Pesticides are also referred to by the type of pest they control. Pesticides can be
either biodegradable pesticides, that break down into harmless compounds by
bacteria and other living organisms, or persistent/Non-Biodegradable pesticides,
which can take months or years to break down.
Insecticides – Insects
Herbicide – Plants
Rodenticides – Rodents (rats & mice)
Bactericides – Bacteria
Fungicides – Fungicide
Larvicides – Larvae
Uses
FORMULATION OF PESTICIDES
A pesticide formulation is a mixture of chemicals which effectively controls
a pest. Formulating a pesticide involves processing it to improve its storage,
handling, safety, application, or effectiveness.1 See the text box on Some
Formulations.
The type of surface, training, equipment, runoff, drift, habits of the pest,
and safety are all considered when a manufacturer designs a pesticide
formulation.
Type of surface
Some formulations are more effective on certain surfaces than others.
Discoloration or pitting of the surface of plants or other surfaces may
occur with some formulations.
Many pesticide products that the public purchases and uses are ready-to-use
(RTU) formulations which require no dilution and can be applied quickly and
conveniently. Examples of ready-to-use formulations used by homeowners
are granules for insect and weed control and baits for rodent control.
Many of the formulations used by farmers and commercial applicators (like
pest control companies) need to be applied with certain equipment. These
formulations may also require certification or training for individuals
performing the application. For example, termiticide applicators may be
required by the Department of Agriculture in each state to complete specific
training in the use of termiticides.
Some liquid pesticide formulations commonly used by farmers and
commercial applicators are applied with a compressed air sprayer, fogger, or
soil injector.6 Other liquid pesticide formulations used by farmers may require
the use of aircraft, low pressure boom sprayer, high-pressure sprayer, or ultra-
low-volume sprayer.6
The equipment required for the application is listed on the label.
Runoff or drift
Rain soon after the application may cause the pesticide to run off and
contaminate lakes, rivers, streams, or ponds.7
Wind may carry or drift the pesticide during the application onto adjacent
property, bodies of water, people, or animals.
Specific environmental precautionary statements may be present on the label
describing how to avoid runoff or drift.
The pesticide product label will list any chemicals that it should not be mixed
with (i.e., incompatible with) or containers that it should not be mixed in. 4 For
example, wettable sulfur should not be mixed with Lorsban or Morestan
because they are incompatible.6
Some pesticides can be mixed together (i.e., they are compatible with each
other).
Not all pesticides can be mixed together (incompatible) because they
separate out of the solution, gel, curdle, or clog the equipment during
application.
Pesticides that are physically different (i.e., dust versus liquid) are typically
incompatible.
Verify with the pesticide label what types of pesticide formulations to avoid
mixing. Formulated pesticide products that are ready-to-use (RTU) liquids and
concentrated liquids that have been diluted according to label instructions
can be mixed together. However, undiluted liquid concentrations should not
be combined.
To reduce incompatibilities of flowable, wettable powder, and water-
dispersible granule formulations, regular shaking is needed.2
If you have questions about compatibility or other pesticide-related issues
contact your State Department of Agriculture or your local County Cooperative
Extension Service for more information.
TOXICITY OF PESTICIDES
Pesticides are designed to control pests, but they can also be toxic (poisonous)
to desirable plants and animals, including humans. Some pesticides are so
highly toxic that very small quantities can kill a person, and almost any
pesticide can make people ill if they are exposed to a sufficient amount.
Because even fairly safe pesticides can irritate the skin, eyes, nose, or mouth, it
is a good idea to understand how pesticides can be toxic so you can follow
practices designed to reduce or eliminate your exposure and the exposure of
others to them.
HOW PESTICIDES ENTER THE BODY
Before a pesticide can harm you, it must be taken into the body. Pesticides can
enter the body orally (through the mouth and digestive system); dermally
(through the skin); or by inhalation (through the nose and respiratory system).
ORAL EXPOSURE
Oral exposure may occur because of an accident, but is more likely to occur as
the result of carelessness, such as blowing out a plugged nozzle with your
mouth, smoking or eating without washing your hands after using a pesticide,
splashing concentrate while mixing, or eating fruit that has been recently
sprayed with a pesticide containing residues above the tolerance set for the
commodity by the Environmental Protection Agency. The seriousness of the
exposure depends upon the oral toxicity of the material and the amount
swallowed.
DERMAL EXPOSURE
Dermal (skin) exposure accounts for about 90% of the exposure pesticide users
receive from nonfumigant pesticides. It may occur any time a pesticide is
mixed, applied, or handled, and it often goes undetected. Both liquid pesticides
and dry materials—dusts, wettable powders, and granules—can be absorbed
through the skin.
Absorption continues to take place on all of the affected skin area as long as the
pesticide is in contact with the skin. The seriousness of the exposure is
increased if the contaminated area is large or if the material remains on the skin
for a period of time.
Rates of absorption through the skin are different for different parts of the body.
Usually, absorption through the forearm is the standard against which
absorption rates in other areas of the body are tested. Absorption is over 11
times faster in the lower groin area than on the forearm (Table 1). Absorption
through the skin in the genital area is rapid enough to approximate the effect of
injecting the pesticide directly into the bloodstream.
INHALATION EXPOSURE
Toxicity is usually divided into two types, acute or chronic, based on the
number of exposures to a poison and the time it takes for toxic symptoms to
develop. Acute toxicity is due to short-term exposure and happens within a
relatively short period of time, whereas chronic exposure is due to repeated or
long-term exposure and happens over a longer period. (Table 2).
All new pesticides are tested to establish the type of toxicity and the dose
necessary to produce a measurable toxic reaction. In order to compare the
results of toxicity tests done in different labs, there are strict testing procedures.
Toxicity testing is extensive (involving many phases) and therefore expensive.
Humans, obviously, cannot be used as test subjects, so toxicity testing is done
with animals and plants. Since different species of animals respond differently
to chemicals, a new chemical is generally tested in mice, rats, rabbits, and dogs.
The results of these toxicity tests are used to predict the safety of the new
chemical to humans.
Toxicity tests are based on two premises. The first premise is that information
about toxicity in animals can be used to predict toxicity in humans. Years of
experience have shown that toxicity data obtained from a number of animal
species can be useful in predicting human toxicity, while data obtained from a
single species may be inaccurate. The second premise is that by exposing
animals to large doses of a chemical for short periods of time, we can predict
human toxicity from exposure to small doses for long periods of time. Both
premises have been questioned.
Chronic toxicity is tested using animal feeding studies. In these studies, the
pesticide under investigation is incorporated into the daily diet and fed to
animals from a very young to a very old age. These, as well as the reproductive
effects studies, are designed to arrive at a No-Observable-Effect-Level (NOEL);
that is, a level in the total diet that causes no adverse effect in treated animals
when compared to untreated animals maintained under identical conditions.
This NOEL is expressed on a mg/kg of body weight/day basis.
A Reference Dose (RfD), also known as Acceptable Daily Intake (ADI), is
usually established at 1/100 of the NOEL, in order to add an additional margin
of safety. The RfD (ADI) is the amount of chemical that can be consumed daily
for a lifetime without ill effects.
ACUTE TOXICITY
The commonly used term to describe acute toxicity is LD50. LD means lethal
dose (deadly amount) and the subscript 50 means that the dose was acutely
lethal to 50% of the animals to whom the chemical was administered under
controlled laboratory conditions. The test animals are given specific amounts of
the chemical in either one oral dose or by a single injection, and are then
observed for a specified time.
The lower the LD50 value, the more acutely toxic the pesticide. Therefore, a
pesticide with an oral LD50 of 500 mg/kg would be much less toxic than a
pesticide with an LD50 of 5 mg/kg. LD50 values are expressed as milligrams per
kilogram (mg/kg), which means milligrams of chemical per kilogram of body
weight of the animal. Milligram (mg) and kilogram (kg) are metric units of
weight. Milligrams per kilogram is the same measure as parts per million. To
put these units into perspective, 1 ppm is analogous to 1 inch in 16 miles or 1
minute in 2 years.
For example, if the oral LD50 of the insecticide parathion is 4 mg/kg, a dose of 4
parts of parathion for every million parts of body weight would be lethal to at
least half of the test animals.
There is no standard measure like the LD50 for chronic toxicity. How chronic
toxicity of chemicals is studied depends upon the adverse effect being studied.
Chronic adverse effects may include carcinogenic effects (cancers), teratogenic
effects (birth defects), mutagenic effects (genetic mutations), hemotoxic effects
(blood disorders), endocrine disruption (hormonal problems), and reproductive
toxicity (infertility or sterility).
CARCINOGENESIS (ONCOGENESIS)
To alert pesticide users to the acute toxicity of a pesticide, a signal word may
appear on the label. Four different categories are used (Table 3). Signal words
are used to tell the user whether the chemical is highly toxic, moderately toxic,
slightly toxic, or relatively non-toxic. These label warnings are based, for the
most part, on the chemical's acute toxicity. For example, the acute oral and
acute dermal toxicity of a pesticide may be in the slightly toxic category. But if
the acute inhalation toxicity is in the highly toxic category, the pesticide label
will have the signal words for a highly toxic pesticide. The degree of eye or skin
irritation caused by the pesticide also influences the signal word.
For chronic toxicity there is no comparable set of signal words like those used
for acute toxicity. Instead, a statement identifying the specific chronic toxicity
problem is sometimes used on the label. Such a statement might read "This
product contains (name of chemical), which has been determined to cause
tumors or birth defects in laboratory animals." Chronic toxicity warning
statements may be accompanied by label directions to wear certain kinds of
protective clothing when handling or working with the pesticide to minimize or
eliminate exposure to the pesticide.
It is important to read the label to look for signal words identifying the product's
acute toxicity and for statements identifying any chronic toxicity problem. A
pesticide may be low in acute toxicity (signal word caution), but it may have a
label statement identifying potential chronic toxicity.
SAFETY FACTORS
Monitoring foods for pesticide residues is carried out by the Food and Drug
Administration (FDA) and the United States Department of Agriculture
(USDA). Crops found to contain residues over the official tolerance (maximum
legal level) established by the EPA must be destroyed. The threat of crop
destruction with resultant financial loss is a strong incentive for farmers to
observe use instructions on pesticide labels and thus assures that residues will
be below established tolerances. Crops grown for export are often checked for
residues by foreign residue laboratories to assure that local tolerance limits are
not exceeded. Lastly, market-basket surveys (analyses of food items from
grocery stores) have confirmed the low exposure of the general public to
pesticides in foods.
HAZARD
Hazard is a function of the toxicity of a pesticide and the potential for exposure
to it. We do not have control of the toxicity of a pesticide because toxicity is a
given characteristic of a particular pesticide; however, we can have control over
our exposure to pesticides. We achieve control over exposure by following
several safety practices including the use of protective clothing and equipment
(PPE).
All pesticides are hazardous if misused, no matter what their toxicity. All
pesticides can be handled safely by using safety practices that minimize or
eliminate exposure to them.
Federal laws regulating pesticides have placed the burden of proving safety of
pesticide usage on the manufacturer. Hazard evaluation studies are generally
done by scientific laboratories maintained by the manufacturer or through
outside contract laboratories. Few products are subjected to the extensive and
vigorous testing pesticides undergo before they are marketed. In fact, many
promising pesticide products are not marketed because they do not pass the
extensive toxicology testing. Older pesticide products that were registered
before the current toxicology testing standards were established are being re-
evaluated to ensure they meet current standards. Precautions and other safety
information found on the product's label are based on information from these
tests. By reading and following the directions on the label, users can minimize
or eliminate hazards due to use of the pesticide to themselves and others.
COMMON PESTICIDE POISONINGS
Cases listed as organophosphates (and the other categories as well) may also
include other insecticides such as carbamates and organochlorine in a single
product. Asymptomatic cases are included in Table 4 only.
CONTROL OF WEEDS
Weed control is important in agriculture. Methods include hand cultivation
with hoes, powered cultivation with cultivators, smothering with mulch,
lethal wilting with high heat, burning, and chemical control with
herbicides (weed killers).
Weed control is a type of pest control, which attempts to stop or reduce growth
of weeds, especially noxious weeds, with the aim of reducing their competition
with desired flora and fauna including domesticated plants and livestock, and in
natural settings preventing non native species competing with native species.
Weed control is important in agriculture. Methods include hand cultivation
with hoes, powered cultivation with cultivators, smothering with mulch,
lethal wilting with high heat, burning, and chemical
control with herbicides (weed killers).
Need for control
Weeds compete with productive crops or pasture, they can be poisonous,
distasteful, produce burrs, thorns or otherwise interfere with the use and
management of desirable plants by contaminating harvests or interfering with
livestock.
Weeds compete with crops for space, nutrients, water and light. Smaller, slower
growing seedlings are more susceptible than those that are larger and more
vigorous. Onions are one of the most vulnerable, because they are slow to
germinate and produce slender, upright stems. .By contrast broad beans produce
large seedlings and suffer far fewer effects other than during periods of water
shortage at the crucial time when the pods are filling out. Transplanted crops
raised in sterile soil or potting compost gain a head start over germinating
weeds.
Weeds also vary in their competitive abilities according to conditions and
season. Tall-growing vigorous weeds such as fat hen (Chenopodium album) can
have the most pronounced effects on adjacent crops, although seedlings of fat
hen that appear in late summer produce only small plants. Chickweed (Stellaria
media), a low growing plant, can happily co-exist with a tall crop during the
summer, but plants that have overwintered will grow rapidly in early spring and
may swamp crops such as onions or spring greens.
The presence of weeds does not necessarily mean that they are damaging a crop,
especially during the early growth stages when both weeds and crops can grow
without interference. However, as growth proceeds they each begin to require
greater amounts of water and nutrients. Estimates suggest that weed and crop
can co-exist harmoniously for around three weeks before competition becomes
significant. One study found that after competition had started, the final yield of
onion bulbs was reduced at almost 4% per day.
Perennial weeds with bulbils, such as lesser celandine and oxalis, or with
persistent underground stems such as couch grass (Agropyron repens)
or creeping buttercup (Ranunculus repens) store reserves of food, and are thus
able to persist in drought or through winter. Some perennials such as couch
grass exude allelopathic chemicals that inhibit the growth of other nearby
plants.
Weeds can also host pests and diseases that can spread to cultivated
crops. Charlock and Shepherd's purse may carry clubroot, eelworm can be
harboured by chickweed, fat hen and shepherd's purse, while the cucumber
mosaic virus, which can devastate the cucurbit family, is carried by a range of
different weeds including chickweed and groundsel.
Pests such as cutworms may first attack weeds but then move on to cultivated
crops.
Some plants are considered weeds by some farmers and crops by
others. Charlock, a common weed in the southeastern US, are weeds according
to row crop growers, but are valued by beekeepers, who seek out places where it
blooms all winter, thus providing pollen for honeybees and other pollinators. Its
bloom resists all but a very hard freeze, and recovers once the freeze ends.
Weed propagation
Seeds
Annual and biennial weeds such as chickweed, annual meadow
grass, shepherd's purse, groundsel, fat hen, cleaver, speedwell and hairy
bittercress propagate themselves by seeding. Many produce huge numbers of
seed several times a season, some all year round. Groundsel can produce 1000
seed, and can continue right through a mild winter, whilst Scentless
Mayweed produces over 30,000 seeds per plant. Not all of these
will germinate at once, but over several seasons, lying dormant in the soil
sometimes for years until exposed to light. Poppy seed can survive 80–100
years, dock 50 or more. There can be many thousands of seeds in a square foot
or square metre of ground, thus any soil disturbance will produce a flush of
fresh weed seedlings.
Subsurface/surface
The most persistent perennials spread by underground creeping rhizomes that
can regrow from a tiny fragment. These include couch grass, bindweed, ground
elder, nettles, rosebay willow herb, Japanese knotweed, horsetail and bracken,
as well as creeping thistle, whose tap roots can put out lateral roots. Other
perennials put out runners that spread along the soil surface. As they creep they
set down roots, enabling them to colonise bare ground with great rapidity. These
include creeping buttercup and ground ivy. Yet another group of perennials
propagate by stolons- stems that arch back into the ground to reroot. The most
familiar of these is the bramble.
Methods
Weed control plans typically consist of many methods which are divided into
biological, chemical, cultural, and physical/mechanical control.
Physical/mechanical methods
Coverings
In a domestic gardens, methods of weed control include covering an area of
ground with a material that creates an unsuitable environment for weed growth,
known as a weed mat. For example, several layers of wet newspaper prevent
light from reaching plants beneath, which kills them.
In the case of black plastic, the greenhouse effect kills the plants. Although the
black plastic sheet is effective at preventing weeds that it covers, it is difficult to
achieve complete coverage. Eradicating persistent perennials may require the
sheets to be left in place for at least two seasons.
Some plants are said to produce root exudates that
suppress herbaceous weeds. Tagetes minuta is claimed to be effective against
couch and ground elder, whilst a border of comfrey is also said to act as a
barrier against the invasion of some weeds including couch. A 5–10 centimetres
(2.0–3.9 in) layer of wood chip mulch prevents some weeds from sprouting.
Gravel can serve as an inorganic mulch.
Irrigation is sometimes used as a weed control measure such as in the case
of paddy fields to kill any plant other than the water-tolerant rice crop.
Manual removal
Many gardeners still remove weeds by manually pulling them out of the ground,
making sure to include the roots that would otherwise allow some to re-sprout.
Hoeing off weed leaves and stems as soon as they appear can eventually
weaken and kill perennials, although this will require persistence in the case of
plants such as bindweed. Nettle infestations can be tackled by cutting back at
least three times a year, repeated over a three-year period. Bramble can be dealt
with in a similar way.
A highly successful, mostly manual, removal programme of weed control in
natural bush land has been the control of sea spurge by Sea Spurge Remote
Area Teams in Tasmania.
Tillage
Weed control through tilling with hoes, circa
1930-40s
Ploughing includes tilling of soil, intercultural ploughing and summer
ploughing. Ploughing uproots weeds, causing them to die. Summer ploughing
also helps in killing pests.
Effect on Water
Make water unfit for consumption.
Agrochemicals in water diffuse with larger water bodies to promote the
growth of algae – which can cause organisms such as fish to die. (This
phenomenon is widely called Fish kills)
Excess chemicals lead to eutrophication.
Leads to water pollution.
Alters the chemical properties of water.
Eutrophication.
Eutrophication, defined as the addition of ‘excess’ nutrients to a water body, is a
widespread environmental problem facing the world’s aquatic habitats.
Eutrophication is the process in which a water body becomes overly enriched
with nutrients, leading to the plentiful growth of simple plant life. The excessive
growth (or bloom) of algae and plankton in a water body are indicators of this
process. Eutrophication is considered to be a serious environmental concern since
it often results in the deterioration of water quality and the depletion of
dissolved oxygen in water bodies. Eutrophic waters can eventually become “dead
zones” that are incapable of supporting life.
Aquatic ecosystems are home to several plant and animal life forms – both simple
and complex. The process of eutrophication destroys the balance in these
ecosystems by favouring the growth of simple plant life. This greatly decreases
the biodiversity of the ecosystem by killing off several desirable species.
Causes of Eutrophication
The availability of nutrients such as nitrogen and phosphorus limits the growth of
plant life in an ecosystem. When water bodies are overly enriched with these
nutrients, the growth of algae, plankton, and other simple plant life is favoured
over the growth of more complex plant life.
Fertilizers
Untreated sewage
Detergents containing phosphorus
Industrial discharge of waste.
Among these sources, the primary contributors to eutrophication include
agriculture and industrial wastes.
Classification of Eutrophication
The process of eutrophication can be categorized into two types based on its root
cause. Both these types are explained in this subsection.
Anthropogenic Eutrophication
Anthropogenic eutrophication is caused by human activity – Agricultural farms,
golf courses, lawns, etc. are supplied with nutrients by humans in the form of
fertilizers. These fertilizers are washed away by rains and eventually find their
way into water bodies such as lakes and rivers.
When introduced to an aqueous ecosystem, the fertilizers supply plentiful
nutrients to algae and plankton, resulting in the eutrophication of the water body.
Overpopulation places a huge demand on industrial and agricultural expansion,
which in turn leads to deforestation. When this occurs, the soil erodes more
easily, resulting in increased soil deposits in water bodies. If the soil is rich in
phosphorus, it can lead to eutrophication and severely damage the ecosystem in
and around the water body.
When sewage pipes and industrial wastes are directed to water bodies, the
nutrients present in the sewage and other wastes increase the rate at which
eutrophication occurs.
Natural Eutrophication
Natural eutrophication refers to the excessive enrichment of water bodies via
natural events. For example, the nutrients from the land can be washed away in a
flood and deposited into a lake or a river. These water bodies become overly
enriched with nutrients, enabling the excessive growth of algae and other simple
plant life.
The process of natural eutrophication is much slower when compared to the
process of anthropogenic eutrophication. This process is also somewhat
dependent on the temperature of the environment. It may even be complemented
by the temperature changes brought on by global warming.
Effects of Eutrophication
Primarily, the adverse effects of eutrophication on aquatic bodies include a
decrease in biodiversity, an increase in toxicity of the water body, and a change
in species dominance. Some other important effects of this process are listed
below.
An image detailing the change in the quality of water in eutrophic water bodies
is provided above.
Decrease in Biodiversity
When an aquatic ecosystem is enriched with nutrients by either natural or
artificial means, the conditions become extremely beneficial to primary
producers. Commonly, algae and other similar species utilize these nutrients and
a huge increase in their population (algal bloom) is observed.
These algal blooms hinder the flow of sunlight to the bottom of the aquatic body
and also cause wide swings in the dissolved oxygen levels in the water.
When the dissolved oxygen in the water reduces to an amount below the hypoxic
level, many marine animals suffocate and die. This reduces the effective
biodiversity of the water body.
Effect on Air
Functions of Auxins
1. Facilitate flowering in plants
2. Used in the process of plant propagation.
3. Used by gardeners to keep lawns free from weeds.
4. Involved in the initiation of roots in stem cuttings.
5. Prevention of dropping of leaves and fruits at early stages.
6. Regulate xylem differentiation and assists in cell division.
7. Auxins are widely used as herbicides to kill dicot weeds.
8. Used to produce fruit without preceding fertilization.
9. Promote natural detachment (abscission) of older leaves and fruits.
10. Apical dominance may occur in which the growth of lateral buds is
inhibited by the growth of apical buds. In such cases, the shoot caps
may be removed.
11. These are produced by the apex of root and shoot.
Gibberellins
Gibberellins are an extensive chemical family based on the ent-
gibberellane structure. The first gibberellin to be discovered was gibberellic
acid. Now there are more than 100 types of gibberellins and are mainly
gathered from a variety of organisms from fungi to higher plants.
They are acidic and are denoted as follows – GA1, GA2, GA3etc.
Functions of Gibberellins
1. Delay senescence in fruits.
2. Involved in leaf expansion.
3. Break bud and seed dormancy.
4. Promote bolting in cabbages and beet.
5. Facilitate elongation of fruits such as apples and enhance their
shape.
6. Used by the brewing industry to accelerate the malting process.
7. Used as the spraying agent to increase the yield of sugarcane by
elongation of the stem.
8. In young conifers, utilized to fasten the maturity period and facilitate
early seed production
9. Helps in increasing the crop yield by increasing the height in plants
such as sugarcane and increase the axis length in plants such as
grape stalks.
10. Gibberellins are acidic in nature.
11. It also delays senescence.
Cytokinins
These are produced in the regions where cell division occurs; mostly in the
roots and shoots. They help in the production of new leaves, lateral shoot
growth, chloroplasts in leaves etc. They help in overcoming apical
dominance and delay ageing of leaves.
Functions of Cytokinins
1. Break bud and seed dormancy.
2. Promotes the growth of the lateral bud.
3. Promotes cell division and apical dominance.
4. They are used to keep flowers fresh for a longer time.
5. Used in tissue culture to induce cell division in mature tissues.
6. Facilitate adventitious shoot formation and lateral shoot growth.
7. Promotes nutrient mobilization that in turn assists delaying leaf
senescence.
8. Helps in delaying the process of ageing (senescence) in fresh leaf
crops like cabbage and lettuce.
9. Involved in the formation of new leaves and chloroplast organelles
within the plant cell.
10. Used to induce the development of shoot and roots along with auxin,
depending on the ratio.
Ethylene
Ethylene is a simple, gaseous plant growth regulator, synthesised by most
of the plant organs includes ripening fruits and ageing tissues. It is an
unsaturated hydrocarbon having double covalent bonds between and
adjacent to carbon atoms.
Ethylene is used as both plant growth promoters and plant growth
inhibitors. Ethylene is synthesized by the ripening fruits and ageing tissues.
Functions of Ethylene
Ethylene is the most widely used plant growth regulator as it helps in
regulating many physiological processes.
1. Induce flowering in the mango tree.
2. Promotes sprouting of potato tubers.
3. Breaks the dormancy of seeds and buds.
4. Enhances respiration rate during ripening of fruits.
5. Applied to rubber trees to stimulate the flow of latex.
6. Facilitates senescence and abscission of both flowers and leaves.
7. Used to stimulate the ripening of fruits. For example, tomatoes and
citrus fruits.
8. Affects horizontal growth of seedlings and swelling of the axis in dicot
seedlings.
9. Increases root hair formation and growth, thus aids plant to expand
their surface area for absorption.