The importance and role of chemicals/ fungicides in plant disease management is the major objective of plant pathology. The need based, effective, ecofriendly application of chemical fungicides can leads sustainable agriculture and food production.

1. MASTER SEMINAR
ON
“Role of chemicals in plant disease management”
Presented By
Mr. Gaikwad Harshvardhan Dattatraya
Seminar In charge
Dr. T. K. Narute
Chairman of Advisory Committee
Dr. S. N. Hasabnis
Assistant Professor (Plant Pathology)
NARP (PZ), Ganeshkhind, Pune.

2. Introduction
Plant disease management:
Measures taken to prevent incidence of a disease, reduce the amount of inoculum that initiates and spreads the disease in
the crop and, finally, minimize the loss caused by the disease have been traditionally called the control measures. Since the
1970 there has been a general tendency to consider the measures as management strategies rather than control because the
control measures generally manage the population of the pathogens at an innocuous level, not necessarily eliminating them
from the ecosystem.
The principles of plant disease management can have two approaches,
1) Management of a single disease of the crop: Management planning for a disease is directed against a specific disease
causing heavy losses, such as late blight of potato, without taking into consideration other fungal, bacterial or virus
diseases of the same crop.
2) Planning for overall health of the crop: Management of crop health involves an integrated plan in which all diseases of
any significant nature for the crop are taken into consideration, although major stress may be against the most common and
severe diseases.
The second approach, though difficult, is of more practical value for the farmer because he is interested in increasing the
productivity of crop and, therefore, prefers a plan that can provide safeguard against all possible diseases occurring in the
area.

3. Plant disease management principles:
1) Immunization: 1) Induction of resistance a) Genetic manipulation b) Systemic acquired resistance
2) Chemotherapy. Use of systemic fungicides and antibiotics
2) Prophylaxis: 1) Legislation: quarantine, seed inspection and certification for
exclusion of pathogen.
2) Avoidance:
a) Choice of geographic area b) Selection of field c) Choice of time of planting
3) Eradication:
a) Rotation b) Sanitation c) Eradication of alternate and collateral hosts d) Chemical
4) Protection:
a) Chemical b) Cultural

4. Plant disease management practices:
1) Cultural practices for disease management
2) Production and use of disease-free propagating material
3) Adjustment of crop culture of minimize disease incidence
4) Field and plant sanitation
5) Biological control
6) Host resistance for disease management
7) Disease management through Toxic Chemicals
*Fungicides, nematicides and antibiotics in use
1) Sulphur fungicides
2) Copper fungicides
3) Mercury fungicides
4) Quinone fungicides
5) Benzene fungicides
6) Heterocyclic Nitrogen compounds
7) Organo Tin compounds
8) Systemic fungicides
9) Antibiotics
10) Nematicides

6. History of chemicals in plant disease management:
1000 B.C. Homer, the Greek poet, made a mention of sulphur with pest controlling properties. (1)
9th Century Surpala’s Vrksayurveda mentions tree wound dressing, tree fumigations, and seed
treatments for control of diseases and pests.
1637 Remnant mentioned the value of seed treatment with sodium chloride for the control of stinking
smut. (2)
1807 Prevost of France showed effectivity of copper sulphate in the control of stinking smut and also
showed adverse effect of copper sulphate on spore germination.
1833 Kendrick of the U.S.A. proposed lime-sulphur preparation against grape mildew. (3)

7. 1882 Millardet of France made his first report on the control of downy mildew of grapes with
Bordeaux mixture.
1904 Lawrence used Bordeaux mixture for the time in India against leaf spot of groundnut
(Cercospora spp.)
1914 A mercurial compound (HgCl2) was used in India for the first by Burns for steeping seed potato
to prevent Rhizoctonia attack.
1940 Burlingham and Reddish proposed the “Zone of Inhibition” technique for fungal seed
protectant.
1952 Kittleson introduced captan as a fungicide.
1975 Triadiamenol (Baytan), another member of triazole group introduced.
1981 Fungicide Resistance Action Committee (FRAC) founded.

8. Fungicides:
1) Sulphur Fungicides:
Elemental sulphur has been in use as a fungicide for a long time and even today
it is one of the best for the control of powdery mildew diseases. The sulphur
fungicides can be classified as follows:
Sulphur fungicides
Inorganic Organic
Elemental Sulphur Lime-sulphur Carbamate fungicides
Dust Wettable

9. 1) Elemental sulphur: It is occurs widely and abundantly in nature, both in the free state and in
combination. Deep in the earth it is found in the elemental state as sulphides and sulphates.
2) Lime-sulphur: Lime-sulphur, or a mixture of calcium polysulphides and calcium thiosulphate (empirical
formulation CaS.Sx) is the product obtained by the combination of lime with sulphur. It has been used
widely for more than 50 years and is still used for some of the common fruit diseases.
Mechanism of fungicidal action:
There are different mechanism of action of elemental sulphur. These various theories were advanced and
later refuted. They are, Hydrogen sulphide theory given by Pollacci, Direct action theory, and finally Owen
advocatesd an interesting theory that polysulphide free radicle, produced metabolic breakdown of 8-
membered rings of elemental sulphur to H2S, might be responcible for toxicity. He suggested that the
reactive polysulphides free radicles might form stable cross-linkages with protein and other cellular
components.

10. 3) Organic sulphur (carbamate) fungicides
Most of these are foliage fungicides, while some of them are used for soil and seed treatments. All
the carbamate fungicides at present available commercially ate derivatives of dithiocarbamic acid.
Ziram: It is the coined name of zinc dimethyldithiocarbamate. The molecular weight of ziram is
305.8. It is soluble to the extent of 65 ppm in water, completely soluble in chloroform. It is white
substance. Mostly used for late and early blight of potato.
Thiram: It is the coined name of tetramethylthirum disulphide or bis (dimethylthiocarbamoyl)
disulphide. The molecular weight of thiram is 240.4. It is unstable in presence of acids. It is white
coloured substance insoluble in water, completely soluble in chloroform. It is used for seed
treatment both as dry powder and as a slurry. It controls damping off, smut, and neck rot of onion,
anthracnose and stem rot of tobacco.

11. 2) Copper Fungicides:
The fungicidal activity of copper sulphate was first recognized in 1807 by Prevost(4), it was
not until 1885 that this fungicidal property was utilized for the production of foliage from
pathogenic fungi. They are widely used to control diseases of plants and commonly used in
plantation crops like tea, rubber and coffee. The copper fungicides can be classified as
follows:

12. Copper fungicides
Copper sulphate Copper Copper Cuprous
Preparations carbonate oxychloride oxide
Preparation preparations preparations
1. Bordeaux mixture Chaubatia paste e.g. Fytolan e.g. Perenox
2. Bordeaux paste Blitox-50, etc. etc.
3. Burgundy Mixture
4. Chestnut Compound

13. A) Copper sulphate preparations:
1) Bordeaux mixture: In 1882 Millardet of France accidently observed the efficacy of copper sulphate against
grape downy mildew caused by Plasmopara viticola. Millardet had proposed the admixture of 100 litres of
water in which 8 kg of bluestone was dissolved with 30 litres of a lime suspension prepared from 15 kg lime.
This formula (8-15-100) was soon found to be too strong and apt to cause foliar injury. The one formula used
relatively often at present time is 4-4-50.
2) Bordeaux paste: Bordeaux paste is consists of the same ingredients as that of Bordeaux mixture, but it is in
paste form. It is primarily used for tree wound dressing to prevent fungal attacks.
3) Burgundy Mixture: It was introduced by Mason in 1887 in Burgundy (France). It is prepared same way as
the Bordeaux mixture, except that lime is substituted by sodium carbonate. It is slightly less effective than
Bordeaux mixture.
4) Chestnut Compound: The compound was suggested by Bewley in 1921. It contains two parts of copper
sulphate and 11 parts of ammonium carbonate. It is used to drench nursery beds for the control of ‘damping-
off’.

14. B) Copper carbonate preparations: This paste was developed at Government Fruit Research Station, Chaubatia in
U.P. This was developed as a wound dressing fungicide to be applied to pruned parts of apple, pear and peach trees
for control of diseases like stem-black, stem-brown, stem canker. The paste is prepared by mixing copper carbonate
(800 gm) in 1 litre of lanolin or raw linseed oil. Advantage: not washed off easily by rains.
C) Copper oxychloride preparations: Due to toxicity of Bordeaux mixture to certain plants, low soluble copper
fungicides are frequently used. Low soluble copper available in India is copper oxychloride. It is formulated both as
wettable power and as ready-to-use dust. Commercial preparations are Blimix 4%, Blitox-50, Cupramar, Micop D-
06, Micop W-50.
D) Cuprous oxide preparations: Harsfall suggested the use of red oxide of copper as a seed treatment fungicide in
1932. In 1939, Heuberger and Horsfall reported that the fungicidal and protective values of the cuprous oxides vary
inversely as the particle size. Fungimar consists of 50 per cent metallic copper in the form of cuprous oxide.
Mechanism of fungicidal action:
Solubilisation hypothesis, Non Solubilisation hypothesis proposed by scientists. The enzymes which require free
sulphhydryl groups for activity appear to be especially susceptible to inactivation by ions of heavy metels. It is
therefore quite possible that copper kills spores by combining with the sulphhydryl groups of certain enzymes.

15. 3) Mercury Fungicides:
Mercurial compounds have been used mostly for treating the seeds to protect them from fungal
attacks. Because of their extreme toxicity, their use for spraying the foliage could not be
encouraged, some compounds are used as fruit and foliage protectants.
Mercurial Fungicides
Inorganic Organic
e.g. Mercurial chloride e.g. Ethyl mercury
Mercurous chloride chloride, Phenyl
Mercury acetate,
etc.

16. Inorganic Mercurials: Hiltner, a German worker, very successfully used mercuric chloride for the control of
Fusarium disease of rye as early as 1910. This was a demonstration of the therapeutic value of mercury
because the mycelium of the fungus remains dormant within the seed. Mercuric chloride was used in India for
treating potato tubers and propagative material of other root crops to protect them from decays during
germination.
Organic Mercurials: The development of organic mercurial resulted from the efforts to find less toxic
substitutes to inorganic mercurial. Organic mercurials are used for treating the seed, dry, wet, or slurry, for the
control of externally seed-borne smuts and various seed and seedling diseases. Germisan, uspulum and tillantin
are organic mercurials used in India.
Mechanism of fungicidal action:
It is generally accepted that the site of action of the fungicidal activity of mercury is at the sulphhydryl (-SH)
groups of the susceptible enzymes. In general, organic mercurial are more toxic than the inorganic one.
Ban on Mercurials: Due to persistence of the organomercuries they get into the food chain. Several countries
are now banned the use of organomercuries. Concept of tolerable concentration instead of zero concentration.

17. 4) Quinone Fungicides:
From quinone group choranil and dichlone are commercially developed, these have proved to be excellent
seed treatment fungicides. Though both these fungicides are unavailable in India.
Cholranil: It was released in 1940 in U.S.A. as a commercial seed dressing fungicide under the trade name
pf Spergon. The molecular weight of chloranil is 245.9 and colour is golden yellow. It is practically in
soluble in water, partially soluble in chloroform.
Dichlone: It is developed as a seed protectant after success of chloranil. Trade name is Phygon, Phygon
XL, etc. The molecular weight of dichloneis 227 and colour is yellow and no odour.
Mechanism of fungicidal action:
Mechanisms: 1) Binding of the quinone nucleus to SH and NH2 groups in the fungus cell 2) disturbance in
the electron transport system- Diclone affects metabolism, inhibit phosphotylation.

18. 5) Benzene Fungicides:
Chlorothalonil is sold as Bravo, Daconil and Termil. It is broad spectrum fungicide.
Dinocap is an acaricide but most commonly used for control of powdery mildew in fruit orchards.
6) Heterocyclic Nitrogen compounds:
This group have some of the best fungicides. Captan is sold under the trade names of Captan, orthocide
Vancide etc. It is used for seed treatment against Pythium and soil drench and foliar spray.
Folpet is closely related to captan effectively used against powdery mildew and some rusts.

19. 7) Organo Tin compounds:
It includes Du-ter is very effective against Cercospora, Helminthosporium, Alternaria. Brestan is
effective against Cercospora, Alternaria. Brestanol have similar activity as Du-ter and Brestan.
Systemic Fungicides:
The discovery of systemic fungicides in 1966. A systemic fungicide is one which is taken up and
translocated within plant as a result of which the later become fungitoxic.
1) Oxathiins, Carboxins and Carboxamides: The first systemic fungicide developed in 1966 were
carboxin (vitavax) and oxycarboxin (plantavax). Both chemicals translocated from roots to control
rust on primary leaves of beans
2) Benzimidazol: They are broad spectrum fungicides. The suppression of fungi in xylem was not
possible but this fuyngicide can do it. e.g. MBC, Bavistin.

20. Presentation of various fungicide available with their origins and relative importance.

21. Role of Chemicals in plant disease management:
Effectively control diseases,
Control diseases before ETL,
If applied in low or recommended dose there will be less environmental losses
Storage period / shelf life is more than natural
Future Aspect:
The chemicals used for the disease management are applied in large amount that’s why the
fungicidal resistance,
residue in environment,
Pollution,
Global warming.
More emphasis on organic or naturally formed chemicals to manage plant disease.

22. References:
Books:
Introduction to principles of plant pathology. R.S. Singh. Oxford & IBH Publishing Co. PVT.
LTD. New Delhi. Fourth Edition, 296-356 pp.
Fungicides in plant disease control. Y.L. Nene and P.N. Thapliyal. Oxford & IBH Publishing Co.
PVT. LTD. New Delhi. Third Edition. 24-160 pp.
Plant pathology diseases and management. A. Mishra, A. Bohra and A. Mishra. Agribios (India).
First Edition. 614 pp.
1 Shepard, H.H. 1939. The chemistry and toxicity of insecticides. Bugress Publ. Co., Minneapolis,
Minn., U.S.A., 383 pp.
2 Woolman, H.M. and H.B. Humphrey. 1924. Summary of literature on bunt or stinking smut of
wheat. U.S. Dep Agric. Bull. 1210:1-44.
3 Lodeman, E.G. 1896. The spraying of plants. Macmillan, New York, 399 pp.

23. Thank You