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Plant Disease management
Pl. Path. 111 (Cr. Hrs. 3+1)
P.N. Sharma
Department of Plant Pathology,
CSK HPKV, Palampur (H.P.)
Disease Management All plant diseases result from a
three-way interaction between
the host,
the pathogen and
the environment.
An epidemic develops if all three
of these factors are favourable to
disease development.
Therefore, disease can be
controlled by manipulating one or
more of these factors so that
conditions are unsuitable for
replication, survival or infection by
the pathogen.
Principles of Disease Management
The history of controlling the diseases is very old,
Man discovered empirical cultural and physical
control practices for crop protection even before
the causal nature of plant diseases.
General acceptance of the idea that fungi can
induce diseases of plant opened the way for
scientific study of means to control diseases and
The principle search was for use of chemical for
disease control. Bovdeaux mixture in 1882 by
Millardet.
Plants resistance to the diseases were
recognized in the nineteenth century (Biffen
1905) by breeding for disease resistant
varieties after the discovery of Mendals’ law
of heredity in 1900.
Success in controlling the diseases with
chemical and host resistance in early 20th
century shifted plant pathologists from
cultural control (Stevens, 1960).
The approach to the management of a
given disease was often based on type
of the disease, economic importance
of the crop and quality or demand of
the market.
Host resistance and cultural practices
were the principal methods used
against pathogens of agronomic crops
because of the low unit value of most
agronomic crops could not justify the
use of chemicals.
Since the main objective of plant
pathology is the economic control of
plant disease. However, the term
control evokes the notion of finality or
completeness, which is not true in
nature. Whereas the word
“Management” conveys the concept of
a continuous process and
management is based on the principle
of maintaining the damage or less
below an “economic injury level”.
The concept of IDM
The philosophy and approach of crop protection have been influenced significantly during last two decade by the evolution of the concept of “IPM”.
This concept has evolved into holistic, multi disciplinary, management system that integrates control methods on the basis of ecological and economic principles for pests of all classes (pathogen, insects induced that exits in an agroecosystem (Glass 1975).
Knowledge of different aspects of disease
development is essential for effective and
economic control.
Cause of the disease.
Mode of survival and spread of the
pathogen.
Host pathogen relationship and mode of
secondary spread.
Effect of environment a pathogeneses
and spread of disease i.e. Epidemiology
knowledge.
TIME-LINE OF INFECTION
Fungal pathogen:
Host:
Preinfection: Germination Germ tube search Appressorium formation Penetration peg
Postinfection Haustorium formation (biotroph) Toxin formation (necrotroph) Detoxification of phytoalexins Reproduction
General induced Papillae Cork & lignin Systemic defenses: formation layers acquired resistance Specific recognition: Hypersensitivity Phytoalexins
structural CONSTITUTIVE DEFENSES chemical
Outside of host Inside of host
Basis of
Disease management principles
Immunization-prophylaxis system: the cure
of diseased plant is not possible because
the disease become visible only after injury
to plant has taken place, thus preventive
measures are most important.
These include preventive measure through
induction of resistance in the host
(immunization) and protection of plant by
prophylactic measures.
Plant disease control Immunization Prophylaxis
Legislation
Cultural
Resistance
Protection
Eradication
Chemotherapy
Destruction
of alternate
hosts
Central State
Rotation Chemicals Sanitation
chemical
Choice of Control Measure
The efficient and economic control of a plant disease is dependent on crop value, effectiveness of control measure, risk involved and cost/benefit ratio. Fruits and vegetables diseases are best controlled
by fungicides whereas
for field crop disease, host resistance is the preferable method.
Management of environment and changes in the cultural practices are desirable in several cases e.g. soil borne disease.
Disease management can be brought about by manipulating the components of the disease pyramid i.e host, pathogen, environment and time.
The host The host can be manipulated by increasing its
resistance to disease, which is the most effective and least expensive method of controlling diseases. However, frequent breakdown of resistance necessitate the Management of the resistance in nature and this can be done by: diverse sources of resistance (e.g. Sonalika and
Girija),
pyramiding of genes for resistance,
deploying genes for resistance in space and time,
use of multlines and the use of horizontally resistant or tolerant cvs.
or by applying chemicals, such as fungicides, that
prevent or halt infections in the plant.
The pathogen The aim of pathogen management is to reduce
inoculum to such a level that economic losses are minimum
The pathogen can be manipulated by excluding or reducing inoculum available to infect plants.
If a particular pathogen is not present in an area then attempts can be made to prevent its introduction.
Quarantine regulations govern the introduction of plant material from high-risk areas. Seed certification schemes also reduce the risk of introducing a new pathogen, and propagating material can be treated to kill any inoculum that is present, before it is introduced to a new area.
The pathogen
The aim of pathogen management is to reduce
inoculum to such a level that economic losses are
minimum
This can be achieved in addition to host resistance, through
the use of chemicals (used only when other methods prove
inadequate).
Chemicals are generally used to crops of high cash values,
against very destructive diseases and in seasons favoring
epidemic development
main aim of managing the pathogen is:
Reducing initial inoculum
Reducing infection rate
Elimination of an existing pathogen is achieved by
chemical and physical treatment and trapping,
crop rotation,
i) Reduction in the initial amount of inoculum can
be brought about by:
Seed treatment (e.g. Vitavax for loose smut of
wheat, barley, bunts,)
Soil treatment e.g. formaldehyde (4%)
Dip treatment of fruits (Thiabendazoles for
storage rots)
quarantine practices and preventative treatments
The pathogen
ii) Reduction in the infection rate can be
achieved by:
Spray chemicals either protectants or systemic.
However, the no. of sprays is dependent on the degree of
freedom from disease desired (which may be high in case of
fruits and vegetables where quality is of paramount
importance)
For field crop, more than one spray may be uneconomic and therefore in such cases Chemicals can be used only if they are inherently more efficient (eg.
Indar (RH124) against leaf rust of wheat
or only against Very destructive diseases e.g. rice blast or
On varieties having a fair degree fo reisistance to disease. Or
In environment not particularly favourable for pathogen development. Or
If forecasting system for judicious use of spray is available (potato blight).
The pathogen
The environment
The environment can be modified so that
it is suitable for plant growth but not for
disease development.
For example, improving soil
drainage, changing the time of sowing,
reducing the density of plants in a crop or
changing irrigation practices can all produce
conditions unfavourable to particular
diseases, while maintaining conditions
suitable for the growth of the plant.
Management of environment
Temperature management by adjusting sowing time to avoid bunt and flag smut of wheat, use of solar heat to eradicate internally seed borne loose smut infection of wheat and barley hot water treatment to eradicate black rot bacterium from cauliflower seeds are typical examples.
Moisture regulation
Irrigation is effective against potato scab, whereas simple water spray under pressure can eradicate powdery mildew.
Flooding of soil can be effective in eradicating Fusarial wilt organism.
Pathogens which are serious in alkaline soil (e.g. Sclerotinia on beans) can be effective controlled by low34ering soil pH to <5.2 by applying sulphur.
Nutritionl status of soil
Affects several soil borne and some airborne diseases. Diseases caused by Rhizoctonia are reduced by nitrate N application. Inorganic N also suppresses S. rolfsii. Adequate N fertilization considerably reduces Helminthosporium on rice and maize. Fusarial wilt can be checked by adequate K nutrition.
Management of cultural practices Proper following of sanitation
Sanitation is effective in greatly reducing incidence of late blight, ring rot and leaf roll of potato.
Use of clean seed or disease free seed is effective in checking different diseases (e.g. potato viruses and bean anthracnose). Harvesting of potato tuber only after defoliation of foliage is effective in preventing tuber rot due to late blight.
Tillage help in soil loosening, thus provide aeration which is effective in preventing/ against Fusarium root rot of beans, Sclerotium rolfsii.
Deep ploughing during dry season followed by a fellow period for nine months destroy the bacterium causing wilt of solanacaeous plants.
Spacing:Disease which spread very fast under crowdy conditions (e.g. Cercospora on pulses) are checked considerably by wide spacing.
Use of organicamendments
4. Time dimensions
Although time dimension is important in
the epidemic development of most
diseases, not much can be done to
manage thus component except the use
of early maturing varieties (e.g. wheat to
escape rust or fast emerging vars. To
escape bunt and flag smut of wheat.
Principle of disease management
The principles of disease
management are generally
based on i) identity of the
disease to be mange
Whetzel (1929) was the first
to classify methods for the
control of disease as :
Exclusion, Eradication,
protection and Resistance,
and later two more methods
were included, avoidance and
Therapy (National Sci.
Academy, 1968).
Six principles
Avoidance
Exclusion
Eradication
protection
Resistance
Therapy
Principles of Plant Disease Management 1. Avoidance of the pathogen
This involves those methods/ practices which avoid the contact of the host with pathogen o susceptible stage of the plant and conditions favorable for the pathogen should not coincide.
Most of diseases can be prevented by selecting suitable site or time of sowing of crop, varietal selection, seed and planting material and by modifying the cultural practices.
Selection of geographical areas
Selection of field
Choice of time of sowing
Disease escaping varieties
Selection of seed and planting material
Modification of cultural practices.
a) Selection of geographical areas
It depends upon suitability of prevailing environmental condition for
particular cop e.g. temp and RH e.g. Certain diseases (fungal and
bacterial) are more serious in wet areas than in dry areas. Thus growing
of such crops in dry areas with irrigation facilities can be avoided from
those diseases e.g. Smut of bajra (Tolyposporium penicillariae) and
ergot of bajra (Cleviceps microsphala) are serious in wet areas.
b) Selection of field
Soil borne diseases can be avoided e.g. Red rot of sugar cane,
late blight, wilt diseases of arhar, root knot nematodes, bacterial
wilt of solnaceous plants.
Selection of site in case fruit crops e.g. Apple trees should not
be planted in areas where oak trees were grown previous to
avoid attack from collar rot (Rosellinia sp.).
c) Choice of time of sowing
In this coincidence of susceptible stage of crop and environment fabourable for
pathogen is taken care off., e.g. Pea and Gram plnted soon after rain, when soil
temp and moisture level are high, shows high incidence of root rot, blight and
wilt. So late sowing (Nov.-Dec.)
d) Disease escaping varieties
The disease escaping quality of varieties due to characteristics of
growth and time of maturity e.g. var. of Pea which matures early (by
January) usually escape damage from powdery mildew and rust.
e) Selection of seeds and planting material
Smuts, red rot of sugarcane, virus free potato tubers etc.
Avoidance of the pathogen
Exclusion It can be defined as a legal restriction of the movement
of agricultural commodities for the purpose of
exclusion, prevention or delay in the spread of plant
pests and diseases in uninfected areas.
Objective of the exclusion is to prevent spread of the
diseaseand this can be achieved by:
Seed treatment
Inspection and certification
Eradication of insect vectors.
Quarantines
Exclusive quarantine or Embargo
Regulatory quarantine
Domestic quarantine
Inspection &Seed Certification
• Setting Certification Standards
• General Seed Certification Standards
– Common for all crops put under certification
• Specific Seed Certification Standards
–Applicable for individual crop or group
of crops.
3. Eradication of the pathogen
Biological control of the pathogens
Crop rotation
Removal and destruction of diseased plants and organs. Rouging
Eradication of alternate and colleteral hosts
Sanitation
Polythene traps and mulches
Control through trap plants
Heat and chemical treatment of diseased plants
Soil treatment
SANITATION
Sanitation involves all procedures that prevent the spread of disease to new plants, plant products, and new areas, or to reduce the amount of inoculum in an already affected area.
It includes thorough washing or chemical treatment of machinery, tools, potting equipment, shoes and hands that will come in contact with multiple plants, washing produce and its containers and storage areas, protecting soil used for propagation from contamination.
Removing and disposing of infected leaves and other plant material is also crucial for reducing the amount of inoculum available to cause new infections.
4. Protection
(For destruction and inactivation of inoculum; involves physical and chemical control methods)
Chemical treatments: (Sprays and seed treatment
Chemical control of insect vectors.
Modification of environment: includes management of physical environment like temp. moisture, light, aeration, pH, nutrition.
Modification of host nutrition
Host Resistance
What is resistance?
It is the ability of a host to hinder/ resist the harmful effects of a
pathogen.
It is a relative term. Resistance can be expressed at any stage of
development of disease.
The resistance is expressed as
Morphological resistance
Biochemical resistance
Classification of resistance
Genetic basis
Monogenic resistance (single gene controlled resistance)
Oligogenic resistance (controlled by two genes)
Polygenic resistance (controlled by more than two genes)
Extra chromosomal resistance (Cytoplasmic resistance e.g.
TMS lines in maize resistant to couthern corn leaf blight
Epidemiological basis of resistance
Van der Plank, (1963) introduced the terms,
“Vertical” and “Horizontal” for resistance.
Vertical resistance vertical resistance is the resistance that is controlled by oe or
two genes and is effective against one or some races of the
pathogen and not against others . VR acts epidemiologically
by decreasing the initial inoculum (X0) but not the rate of
increase (r) of virulent races or checks the epidemic.
Horizontal resistance horizontal resistance is controlled by manu genes
and is effective against all races of the pathogen.
HR reduces the rate of spread of disease (r) i.e.
slows down the epidemic.
Vertical resistance
Is monogenic or oligogenic.
VR is also called as
differential resistance, field
immunity, hypersensitive
resistance, major gene
resistance, qualitative
resistance, R-gene resistance,
race -specific resistance, and
specific résistance.
VR is a temporary resistance
but provides a complete
control of disease against
specific race
Checks the epidemic
Horizontal resistance
Controlled by many
genes
is also called Race non
specific resistance, minor
gene resistance,
quantitative resistance,
general resistance,
durable resistance,
partial resistance
It is permanent
resistance
Slows down the
epidemic
Apparent resistance It is generally a result of disease escape or
tolerance to disease
Disease escape: it occurs when genetically
susceptible plant do not become infected because
of non coincidence of susptble stage with
favouorable condiditions or duw to fast growth rate
of host as compared to pathogen or due to mixed
cropping or age of the host plant
Disease tolerance: it’s the ability of the plant to
produce a good crop even when its attacked by the
pathogen.
Development of resistant varieties The resistance varieties can be developed by using following
methods
Selection oh host for resistance
Hybridization using resistant (R) and agronomically superior
susceptibe (S) varieties
Resistance from various sources
Crossing between R and S parents
Mutation
Physical mutagens X-rays; UV rays etc
Chemical mutagens: EMS
Resistance through host nutrition
Cross protection
Induced resistance
SAR
CP mediated resistance
Use of genetic engineering: resistance can be transferred to a plant
species from alien sources e.g. BT gene in cotton crom bacteria
Bacillus thuringiensis
Management of Resistance
The following strategies of R-gene management are
available.
Pyramiding of vertical genes
Regional deployments of vertical genes
Rotation of vertical genes or gene cycling.
Intra-specific within field diversity by genotype mixtures
Cultivar mixtures
Multilines
6. Therapy
Chemotherapy
Chemical seed treatment
Thermotherapy
Hot water or air treatment
Tree surgery
Removal of disease part and treatment with
chemicals
Integrated disease management
Integrated disease management uses all suitable techniques that complement each other with the aim of keeping the disease below the threshold at which economic damage occurs.
This approach also aims to avoid the problem of developing resistance in pathogens to widely used fungicides or antibiotics.
In IDM, various control measures are combined for effective and economic management of the disease e.g. Resistant crop varieties might be used in conjunction with chemical treatment, crop rotation and manipulation of the environment.
Multiple approaches to disease management are particularly useful when the disease cycle is not fully understood.