Lecture 10. Protection – Physical methods of protection - Chemical fungicides – Ideal
characters - formulations and adjuvants - Safety measures to be followed
while handling fungicides
Eradication
Eradication is the extermination or killing or destruction of the pathogen
Eradication of pathogen from seed materials
Eradication of plant pathogens from the seed and seed materials can be achieved both my
mechanical and physical methods.
Mechanical methods
i. Sieving of seed with appropriate sieve in order to remove the ergot infected seeds in
millets especially pearlmillet ergot (Claviceps fusiformis) and ergot of rye (C. purpurea).
The ergot infected seeds or the ergots or the sclerotia are larger in size when compared
to healthy grains. So they can be easily removed by simple sieving method.
ii. The ergot infected seeds can also be removed by soaking the seeds in 20% brine
solution (common salt solution). The infected grains are lighter in weight and there by
the infected grains will float on the surface in salt solution. They can easily be collected
and removed. After soaking, the seeds must be washed thoroughly to remove the salt
from the seed surfaces. This method can also be employed for the tundu disease in
wheat (caused by the bacterium, Corynebacterium tritici and the nematode, Anguina
tritici)
Physical methods
The physical agents viz., sunlight or solar heat, hot water, hot air and steam can be used to kill
the pathogens present in the seed or seed materials.
i. Sunlight / solar heat
One of the best example for the solar treatment is the Luthras’ solar treatment for the
management of loose smut disease in wheat (caused by Ustilago nuda tritici, an internally seed
borne pathogen). This method was proposed by J.C. Luthra during the year 1941. In this
method the wheat seeds must be soaked in ordinary water for about four hours from 8am to 12
noon and the seeds must be spread over a cement floor during the after noon from 12 noon to
4pm, when the temperature is ≥ 39 0C. The dormant mycelium present in the seed get
germinated or activated and start sprouting, while it is soaked in water and when it is spread
over a cement floor they will be killed easily.
, ii. Hot water treatment
The sugarcane grassy shoot phytoplasma is killed when the sugarcane setts are treated with
hot water at a temperature of 500C for 2.30h.
iii. Hot air treatment
Similarly, the hot air (at 54 0C for 8 hours) can also be used to kill the sugarcane grassy shoot
phytoplasma.
iv. Steam
The steam can also be used to kill the seed borne pathogens like Xanthomonas orzae pv.
oryzae (bacterial leaf blight pathogen of rice) and Helminthosporium oryzae (brown spot
pathogen of rice). The temperature must be between 52 to 54 0C and seeds must be treated for
20 minutes.
Aerated steam therapy: This is a special method of steam therapy to kill the phytoplasma in
grassy shoot infected sugarcane setts. The setts are spread over the shelves through which the
steam is passed by the instrument at a temperature of 500C for 1hour.
Soil Solarization
Soil solarization is a physical method (of soil-disinfestation) using solar heat by
mulching a soil with a transparent polyethylene sheet during hot season to kill soil
borne pathogens
Usually 25 micron transparent polyethylene film
Advantages
Suppress pests and pathogens
Weed control
, Increase plant growth response by conserving moisture
Beneficially altering the soil microbiome
Altering the solubility of minerals and organic matter
Incineration
It is a physical method for eradication of pathogens
Incineration is a process that involves the combustion of substances contained in plant
materials infected with pathogens - Tree crops like Citrus canker - lopping and
incineration
Burning of infected stubbles usually done – Sugacane red rot, Rice sheath blight
FUNGICIDES
The word ‘fungicide’ originated from two Latin words viz., ‘fungus’ and ‘caedo’. The word ‘caedo’
means ‘to kill’. Thus the fungicide is any agency which has the ability to kill the fungus. Hence,
fungicide is a chemical which is capable of killing fungi.
Fungistat
Some chemicals do not kill the fungal pathogens. But they simply arrest the growth of the
fungus temporarily. These chemicals are called fungistat and the phenomenon of temporarily
inhibiting the fungal growth is termed as ‘fungistasis’.
Antisporulant
Some other chemicals may inhibit the spore production without affecting the growth of
vegetative hyphae and are called as ‘antisporulant’.
Antipenetrant
A chemical that exhibits poor or no antifungal activity under in vitro conditions but provides
protection to the plants against diseases by inhibiting the penetration of host surface by the
, fungi is called antipenetrant. Examples - Tricyclazole, Pyroquilon, Edifenphos, Iprobenphos
and Carpropamid against rice blast, Quinoxyfen against powdery mildew.
Characteristics of an ideal fungicide
Low phytotoxicity
Stability in storage
Stability after dilution to spray strength
Should not be toxic to humans, animals, earth worms and other beneficial microbes
Easily available in market with cheap price
Availability in different formulations
Broad spectrum of activity
Compatible with other agrochemicals
Ease transport
Fungicides can be broadly grouped based on their (i) mode of action (ii) general use and (iii)
chemical composition.
I. Based on mode of action
1. Protectant
Protectant fungicides are prophylactic in their behaviour. Fungicide which is effective only if
applied prior to fungal infection is called a protectant.
eg., Zineb, Sulphur.
2. Therapeutant
Fungicide which is capable of eradicating a fungus after it has caused infection and there by
curing the plant is called chemo therapeutant. Usually chemo therapeutant are systemic in their
action. eg. Carboxin, Oxycarboxin.
3. Eradicant
Eradicant are those which remove pathogenic fungi from an infection court (area of the host
around a propagating unit of a fungus in which infection could possibly occur). eg. Organic
mercurial, lime sulphur, dodine etc. These chemicals eradicate the dormant or active pathogen
from the host. They can remain effective on or in the host for some time.
II. Based on general uses
The fungicides can also be classified based on the nature of their use in managing the
diseases.
1. Seed protectants : Captan, thiram, organomercuries,carbendazim, carboxin etc.
characters - formulations and adjuvants - Safety measures to be followed
while handling fungicides
Eradication
Eradication is the extermination or killing or destruction of the pathogen
Eradication of pathogen from seed materials
Eradication of plant pathogens from the seed and seed materials can be achieved both my
mechanical and physical methods.
Mechanical methods
i. Sieving of seed with appropriate sieve in order to remove the ergot infected seeds in
millets especially pearlmillet ergot (Claviceps fusiformis) and ergot of rye (C. purpurea).
The ergot infected seeds or the ergots or the sclerotia are larger in size when compared
to healthy grains. So they can be easily removed by simple sieving method.
ii. The ergot infected seeds can also be removed by soaking the seeds in 20% brine
solution (common salt solution). The infected grains are lighter in weight and there by
the infected grains will float on the surface in salt solution. They can easily be collected
and removed. After soaking, the seeds must be washed thoroughly to remove the salt
from the seed surfaces. This method can also be employed for the tundu disease in
wheat (caused by the bacterium, Corynebacterium tritici and the nematode, Anguina
tritici)
Physical methods
The physical agents viz., sunlight or solar heat, hot water, hot air and steam can be used to kill
the pathogens present in the seed or seed materials.
i. Sunlight / solar heat
One of the best example for the solar treatment is the Luthras’ solar treatment for the
management of loose smut disease in wheat (caused by Ustilago nuda tritici, an internally seed
borne pathogen). This method was proposed by J.C. Luthra during the year 1941. In this
method the wheat seeds must be soaked in ordinary water for about four hours from 8am to 12
noon and the seeds must be spread over a cement floor during the after noon from 12 noon to
4pm, when the temperature is ≥ 39 0C. The dormant mycelium present in the seed get
germinated or activated and start sprouting, while it is soaked in water and when it is spread
over a cement floor they will be killed easily.
, ii. Hot water treatment
The sugarcane grassy shoot phytoplasma is killed when the sugarcane setts are treated with
hot water at a temperature of 500C for 2.30h.
iii. Hot air treatment
Similarly, the hot air (at 54 0C for 8 hours) can also be used to kill the sugarcane grassy shoot
phytoplasma.
iv. Steam
The steam can also be used to kill the seed borne pathogens like Xanthomonas orzae pv.
oryzae (bacterial leaf blight pathogen of rice) and Helminthosporium oryzae (brown spot
pathogen of rice). The temperature must be between 52 to 54 0C and seeds must be treated for
20 minutes.
Aerated steam therapy: This is a special method of steam therapy to kill the phytoplasma in
grassy shoot infected sugarcane setts. The setts are spread over the shelves through which the
steam is passed by the instrument at a temperature of 500C for 1hour.
Soil Solarization
Soil solarization is a physical method (of soil-disinfestation) using solar heat by
mulching a soil with a transparent polyethylene sheet during hot season to kill soil
borne pathogens
Usually 25 micron transparent polyethylene film
Advantages
Suppress pests and pathogens
Weed control
, Increase plant growth response by conserving moisture
Beneficially altering the soil microbiome
Altering the solubility of minerals and organic matter
Incineration
It is a physical method for eradication of pathogens
Incineration is a process that involves the combustion of substances contained in plant
materials infected with pathogens - Tree crops like Citrus canker - lopping and
incineration
Burning of infected stubbles usually done – Sugacane red rot, Rice sheath blight
FUNGICIDES
The word ‘fungicide’ originated from two Latin words viz., ‘fungus’ and ‘caedo’. The word ‘caedo’
means ‘to kill’. Thus the fungicide is any agency which has the ability to kill the fungus. Hence,
fungicide is a chemical which is capable of killing fungi.
Fungistat
Some chemicals do not kill the fungal pathogens. But they simply arrest the growth of the
fungus temporarily. These chemicals are called fungistat and the phenomenon of temporarily
inhibiting the fungal growth is termed as ‘fungistasis’.
Antisporulant
Some other chemicals may inhibit the spore production without affecting the growth of
vegetative hyphae and are called as ‘antisporulant’.
Antipenetrant
A chemical that exhibits poor or no antifungal activity under in vitro conditions but provides
protection to the plants against diseases by inhibiting the penetration of host surface by the
, fungi is called antipenetrant. Examples - Tricyclazole, Pyroquilon, Edifenphos, Iprobenphos
and Carpropamid against rice blast, Quinoxyfen against powdery mildew.
Characteristics of an ideal fungicide
Low phytotoxicity
Stability in storage
Stability after dilution to spray strength
Should not be toxic to humans, animals, earth worms and other beneficial microbes
Easily available in market with cheap price
Availability in different formulations
Broad spectrum of activity
Compatible with other agrochemicals
Ease transport
Fungicides can be broadly grouped based on their (i) mode of action (ii) general use and (iii)
chemical composition.
I. Based on mode of action
1. Protectant
Protectant fungicides are prophylactic in their behaviour. Fungicide which is effective only if
applied prior to fungal infection is called a protectant.
eg., Zineb, Sulphur.
2. Therapeutant
Fungicide which is capable of eradicating a fungus after it has caused infection and there by
curing the plant is called chemo therapeutant. Usually chemo therapeutant are systemic in their
action. eg. Carboxin, Oxycarboxin.
3. Eradicant
Eradicant are those which remove pathogenic fungi from an infection court (area of the host
around a propagating unit of a fungus in which infection could possibly occur). eg. Organic
mercurial, lime sulphur, dodine etc. These chemicals eradicate the dormant or active pathogen
from the host. They can remain effective on or in the host for some time.
II. Based on general uses
The fungicides can also be classified based on the nature of their use in managing the
diseases.
1. Seed protectants : Captan, thiram, organomercuries,carbendazim, carboxin etc.
