This document discusses the importance of biological control over chemical control for managing plant diseases. It notes that plant pathogens can infect most crop types and reduce yields. While chemicals are widely used to control bacteria, fungi and nematodes, there are concerns about pathogen resistance, environmental contamination, and human/animal toxicity. Biological control uses organisms like beneficial bacteria, fungi and insects to naturally reduce pathogens through competition, antibiotics or predation. It has benefits like lower impact on other organisms, compatibility with natural enemies, and no toxic residues. The document concludes that biological products are a more sustainable approach to pest control as chemicals are phased out due to resistance or commercial viability issues.

1. Importance of
Biological Control
instead of
Chemical Control for
Plants

2.  A plant pathogen is a broad term that refers
to any of the organisms, such as fungi,
bacteria, protists , nematodes, and viruses
that cause plant diseases.
 Plant pathogens that cause plant diseases
reduce a grower's ability to produce crops
and can infect almost all types of plants.

3. Fig- Schematic representation of the basic functions in a plant (left) and of the kinds of
interference with these functions (right) caused by some common types of plant diseases.

4. Crops Name of Diseases Name of pathogen Location
1. Rice Brown spot of Rice (Fungal) Drechslera oryzae Externally
2. Wheat Leaf Blight of wheat ( Fungal) Alternaria triticina Externally &
internally
3. Barley Loose smut of barley(Fungal) Ustilago nuda Internally
4. Rice Bacterial blight of rice (Bacteria) Xanthomonas
campestris pv. oryzae
Internally
5. Cotton Angular leaf spot of cotton
(Bacteria)
Xanthomonas
campestris pv. oryzae
Externally &
internally
6. Potato Brown rot of potato ( Bacteria) Xanthomonas
compestris pv.
malvacearum
Seed borne
7. Bean Mosaic of bean (Virus) Common bean mosaic
virus
Internally
8. Potato Leaf roll of potato (Virus) Potato virus-1 Infected seed tuber
9. Rice Ufra disease or rice (Nematode) Ditylenchus angustus Externally

5.  Blight- A disease characterised by widespread death of plant tissue.
 Canker- A sunken necrotic lesion often of a main stem, branch or root.
 Damping Off-Collapse and rot of seedlings near soil level before emergence or soon after
emergence caused by Pythium spp., Phytophthora spp., Fusarium spp., and Rhizoctonia spp.
 Downey mildew- White or grey 'bloom' on leaves and stems caused by production of
sporangiophores and sporangia by members of the Peronosporales (downy mildew fungi).
 Gall- An abnormal growth or swelling produced as a result of pathogenic invasion.
 Mosaic- Patchy variation of normal green colour in leaves, usually light and dark green mosaic,
 symptomatic of many viral diseases.
 Powdery mildew-White powdery 'bloom' on the plant surface caused by the production of fungal
mycelium,conidiophores and conidia by members of the Erysiphales (powdery mildew fungi).
 Pustule- A blister-like spore mass breaking through a plant epidermis.
 Rot- Disintegration of tissue, often caused by enzymes or toxins produced by pathogens.
 Rust- Rust-coloured pustules formed by members of the Uredinales (rust fungi).
 Scab- A discrete, superficial roughened lesion.
 Smut- A disease characterised by black spore masses on leaves, stems or inflorescences, caused
by members of the Ustilaginales (smut fungi).
 Vascular Wilt-A disease in which the pathogen is confined to the vascular system of the host and
in which wilting is a characteristic symptom; plants lose their turgidity and become flaccid, leaves
collapse.

6. Loose smut of
barley(Fungal)
Brown spot of Rice
(Fungal)
Mosaic of bean
(Virus)
Brown rot of potato
(Bacteria)
Leaf Blight of wheat
(Fungal)
Earcockle of wheat
(Nematode)

8.  A variety of chemicals are available that have
been designed to control plant diseases
by inhibiting the growth of or by killing the
disease-causing pathogens.
 Chemicals used to control bacteria
(bactericides), fungi (fungicides), and
nematodes (nematocides) may be applied to
seeds, foliage, flowers, fruit, or soil.

9.  Listed some effects of chemicals on plant diseases:-
Name of Chemical Name of plant disease Used to control
1. Copper compound
(Bordeaux mixture)
Downy mildew of grape,
Bacterial leaf spot etc
Fungicides,Bactericides
2.Sulfer compound Powdery mildews,certain
rusts, leaf blight
Fungicides
3. Carbonate compounds
(sodium biocarbonate)
Black spot fungus of rose,
Grey mold fungus etc
Fungicides
4. Organophosphate Gall formation of
Nematodes, Downy
mildew etc
Nematocides, Fungicides
5. Organic Sulfer
compound
(Dithiocarbamates)
Foliage disease etc. Fungicides

10.  They prevent or reduce infections by utilizing
various principles of disease control.
 Eradicants are designed to kill a pathogen
that may be present in the soil, on the seeds,
or on vegetative propagative organs, such as
bulbs, corms, and tubers.
 Protectants place a chemical barrier between
the plant and the pathogen.
 Therapeutic chemicals are applied to combat
an infection in progress.

11.  Soil treatments are designed to kill soil
inhabiting nematodes, fungi, and bacteria.
 This eradication can be accomplished using
steam or chemical fumigants.
 Soilborne nematodes can be killed by applying
granular or liquid nematicides.
 Most soil is treated well before planting;
however, certain fungicides can be mixed with
the soil at planting time.

12.  Protective sprays and dusts applied to
the foliage and fruit of crops and ornamentals
include a wide range of organic chemicals designed
to prevent infection.
 Protectants are not absorbed by or translocated
through the plant; thus they protect only those parts
of the plant treated before invasion by the pathogen.
 A second application is often necessary because the
chemical may be removed by wind, rain, or irrigation
or may be broken down by sunlight.
 New, untreated growth also is susceptible to
infection.
 New chemicals are constantly being developed.

13.  Pathogen resistance to chemical agents has been a
problem since the 1970s.
 Throughout the 1980s and 1990s, public concern has
grown about the use of agricultural chemicals in general.
 The main concerns are the risk of poisoning humans or
animals, contamination of livestock products, harm to
beneficial insects, and the contamination of food
products, waterways and soil.
 When properly used, fungicides should not cause
problems in any of these areas, but they do have the
potential to alter the balance of diseases on certain
crops.

14.  Biological control of plant diseases involves
the use of organisms other than humans to
reduce or prevent infection by a pathogen.
 These organisms are called antagonists; they
may occur naturally within the host’s
environment, or they may be purposefully
applied to those parts of the potential host
plant where they can act directly or indirectly
on the pathogen.

15.  Generally Biological controls
consist of three different parts:-
1. Macrobials
2. Microbials
3. Biochemicals

16.  Biological control assumes that natural
predators or parasites are able to suppress pests.
 Initially, therefore, natural enemies were
imported to control the pests.
 These natural predators were released in small
numbers, but once they became established
they were effective in the long term.This
method is also called inoculation.
 When the natural predator is introduced
periodically, it is known as inundation.

17.  Several beneficial micro-organisms can also be
used to improve plant health and control pests
and diseases.
 Bacteria, fungi and other micro-organisms can
have these effects because they compete for
nutrients or space, they produce antibiotics or
they simply eat other harmful microorganisms.
 Some examples of commonly used microbials
areTrichoderma and Bacillus subtilis

18.  In addition to macro-organisms and micro-
organisms, there are also resources of natural
origin and pheromones which can be used to
control pests and diseases.
 This category is very wide, including plant
extracts, vitamins and plant hormones.
 These also work preventively to make plants
strong and healthy.
 The pheromones are used to lure the pest (insects)
into a trap. Sex pheromones and aggregating
pheromones are the most commonly used types.

20.  Biological products, known as biopesticides,
can play a significant role in a more
 sustainable food chain as chemical pesticides
are withdrawn due to resistance problems or
because they are no longer commercially
viable, according to the research. Chemicals
also endanger workers' health and can
contaminate groundwater.

21.  Biological control agents such as naturally
occurring fungi, bacteria or viruses are
applied in much the same way as chemical
pesticides to fight insect pests, but have
obvious benefits as they have little impact on
other organisms, are compatible with other
natural enemies, do not leave toxic residues
and are relatively cheap to develop.These far
outweigh the disadvantages of lower
effectiveness and a shorter shelf life.

24.  Biological pest control notes from the University of California
 What Is BiologicalControl? from Cornell University
 Information about biopesticides from the EPA (Environmental ProtectionAgency)
 Ideas for natural homemade insecticides fromTreeHugger
 Facts about chemical pesticides fromToxTown (an NIH or National Institutes of
Health site)
 Principles of integrated pest management from the EPA
 The EnvironmentalWorking Group has a Dirty Dozen list as well as other
information about pesticide residues on food.
 The National Pesticide Information Center is a useful resource for pest control and
pesticide safety information.
 The website is run by Oregon State University and the U.S. Environmental
ProtectionAgency.
 GEORGE N. AGRIOS, Plant Pathology, 5th ed.
 Compilations of practical information are A. JOHNSTON and C. BOOTH (eds.), Plant
Pathologist’s Pocket Book, 2nd ed. (1983), on the identification, isolation, and
culture of plant pathogens; MICHAEL D. SMITH (ed.),
 The Ortho Problem Solver, 3rd ed. (1989), a handbook for indoor and outdoor
plants; Westcott’s Plant Disease Handbook, 5th ed. rev. by R. KENNETH
HORST (1990),