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LECTURE 15
PROTECTION : Use of chemicals for the control of plant diseases is generally referred to as protection or therapy.
Protection : The prevention of the pathogen from entering the host or checking the further development in already infected plants by the application of chemicals is called protection and the chemicals used are called protectants.
Therapy means cure of a disease, in which fungicide is applied after the pathogen is in contact with the host. Chemicals used are called therapeutants. Fungicide : Any agent (chemical) that kills the fungus
Fungistat : Some chemicals which do not kill fungi, but simply inhibit the fungus growth temporarily.
Antisporulant : The chemical which inhibits spore production without affecting vegetative growth of the fungus.
Fungicides are classified into three categories: Protectants, eradicants and therapeutants.
1. Protectants : These are the chemicals which are effective only when used before infection (prophylactic in behavior). Contact fungicides which kill the pathogen present on the host surface when it comes in contact with the host are called protectants. These are applied to seeds, plant surfaces or soil. These are non-systemic in action (i.e, they cannot penetrate plant tissues). Ex: Zineb,sulphur, captan, Thiram, etc. 2. Eradicants : Those chemicals which eradicate the dormant or active pathogen from the host. They can remain on/in the host for some time. Ex: Lime sulphur, Dodine. 3. Therapeutants : These are the agents that inhibit the development of a disease syndrome in a plant when applied after infection by a pathogen. Therapy can be by physical means (solar and hot water treatment) and chemical means (by use of systemic fungicides, i.e., chemotherapy).
CLASSIFICATION OF FUNGICIDES BASED ON CHEMICAL NATURE
Many fungicides have been developed for purpose of managing crop diseases which may be used as sprays, dusts, paints, pastes, fumigants, etc. The discovery of Bordeaux mixture in 1882 by Professor Millardet, University of Bordeaux, France led to the development of fungicides. Major group of fungicides used include salts of toxic metals and organic acids, organic compounds of sulphur and mercury, quinones and heterocyclic nitrogenous compounds. Copper, mercury, zinc, tin and nickel are some of the metals used as base for inorganic and organic fungicides. The non metal substances include, sulphur, chlorine, phosphorous etc. The fungicides have been classified based on their chemical nature as follows
COPPER FUNGICIDES: Copper fungicides can be classified as preparatory and proprietory copper compounds.
PREPARATORY COPPER FUNGICIDES
Common name Chemical composition Diseases managed
- Bordeaux mixture
It is prepared by suspending 5 Kg of copper sulphate and 5 Kg of lime in 500 liters of water (1%)
Downy mildew of grapes, Coffee rust, Tikka leaf spot of groundnut, citrus canker, citrus scab, etc.
2.Bordeaux paste It is prepared by mixing 1 Kg of copper sulphate and 1 Kg of lime in 10 liters of water
It is a wound dressing fungicide and can be applied to the pruned parts of the host plants such as fruit crops and ornamentals. Ex: Citrus gummosis, Stem bleeding of coconut, Bud rot of coconut, etc.
3.Burgundy mixture
Sodium carbonate is used in place of lime. It is prepared by mixing 1 Kg of copper sulphate and 1 Kg of sodium carbonate in 100 liters of water
Downy mildew of grapes, Coffee rust, Tikka leaf spot of groundnut, citrus canker, citrus scab
4.Cheshunt compound
It is a compound prepared by mixing 2 parts of copper sulphate and 11 parts of ammonium carbonate
It is used for soil drenching only. Sclerotial wilt diseases of chilli, tomato and groundnut. Fusarial wilt diseases. Damping-off diseases of solanaceous crops. 5.Chaubattia paste
It is a compound prepared by mixing 800g of copper sulphate and 800g of red lead in 1 liter of lanolin or linseed oil
Pink disease of citrus, stem canker and collar rot of apple and pears
Proprietary copper fungicides or Fixed or insoluble copper fungicides: In the fixed or insoluble copper compounds, the copper ion is less soluble than in Bordeaux mixture. So, these are less phytotoxic than Bordeaux mixture but are effective as fungicides.
Common name Trade name Dosage Disease managed
- Copper oxy chloride
Blitox-50, Blue copper- 50, Cupramar- 50
0.3 to 0.5% for foliar application, 25 to 35 Kg/ha for dusting
Anthracnose of grapevine, Tikka leaf spot of groundnut, Sigatoka leaf spot of banana, citrus canker, black arm of cotton
- Cuprous oxide Fungimar and Perenox
0.3% for foliar spray Anthracnose of grapevine, Tikka leaf spot of groundnut, Sigatoka leaf spot of banana, citrus canker, black arm of cotton
- Copper hydroxide Kocide 0.3% for foliar spray Blister blight of tea, False smut of rice, Tikka leaf spot of groundnut
SULPHUR FUNGICIDES Sulphur is probably the oldest chemical used in plant disease management for the control of powdery mildews and can be classified as inorganic sulphur and organic sulphur. Inorganic sulphur fungicides include lime sulphur and elemental sulphur fungicides. Organic sulphur fungicides, also called as carbamate fungicides, are the derivatives of dithiocarbamic acid.
INORGANIC SULPHUR FUNGICIDES Common name Trade name Dosage Disease managed Preparatory sulphur compounds
- Lime sulphur It is prepared by mixing 20 Kg of rock lime and 15 Kg of sulphur in 500 liters of water
10-15 liters in 500 liters of water
Powdery mildew of apple, Apple scab, bean rust
- Sulphur dust Kolo dust, Mico- 999
4-5g/Kg seed for ST, 10-30 Kg/ha for dusting on crops, 100 Kg /ha for soil application in tobacco, 500 Kg/ha for furrow application in potato
Common scab of potato, Grain smut of jowar, Powdery mildew of tobacco, chilli, rose, mango, grapes, etc.
- Wettable sulphur Sulfex, Thiovit, Cosan
0.2-0.4 % for foliar spray
Powdery mildews of various crops
Common name Trade name Dosage Diseases managed 1.Captan (Kittleson’s killer)
Captan 50W, Captan 75 W, Esso fungicide, Orthocide 406, Hexacap, Vancide 89
0.2 to 0.3% for dry seed treatment, 0. to 0.3% for foliar spray, 25 to 30 Kg/ha for furrow application
Onion smut, Chilli die-back and fruit rot, Damping off of beans, chilli and tomato, seed rots and seedling blights of maize
- Folpet Phaltan 0.1 to 0.2% for spraying
Apple scab, tobacco brown spot, rose black spot 3.Captafol Difosan, Difolaton, Sanspor, Foltaf
0.15 to 0.2% for spraying, 0.25% for seed treatment, 0.15% for soil drenching
Sorghum anthracnose, cotton seedling diseases, seed rot and seedling diseases of rice, downy mildew of crucifers, apple scab
- Iprodione Rovral, Glycophene 0.1 to 0.2% for foliar application
Diseases caused by Botrytis, Monilinia, Alternaria, Sclerotinia, Helminthosporium and Rhizoctonia
- Vinclozolin Ornalin, Ronilan, Vorlan
0.1 to 0.2% for foliar application
Effective against sclerotia forming fungi like Botrytis, Monilinia and Sclerotinia
MISCELLANEOUS FUNGICIDES Common name Trade name Dosage Diseases managed
- Chlorothalonil Bravo, Daconil, Kavach, Thermil, Exotherm, Safegaurd
0.2 to 0.3% for foliar application
A broad spectrum contact fungicide often used in greenhouses for control of Botrytis on ornamentals and for several molds and blights of tomato. Also used for the control of sigatoka leaf spot of banana, onion purple blotch, tikka leaf spot and rust of groundnut
- Dinocap Karathane, Arathane, Capryl, Mildex, Mildont and crotothane
0.1 to 0.2% for spraying
It is a good acaricide and contact fungicide and it controls powdery mildews of fruits and ornamentals effectively. This can be safely used on sulphur sensitive crops like cucurbits and apple varieties for control of powdery mildews
- Dodine Cyprex, Melprex, Guanidol and Syllit
0.075% for spraying Apple scab, black spot of roses and cherry leaf spot
SYSTEMIC FUNGICIDES
The systemic fungicides were first introduced by Von Schelming and Marshall Kulka in
- The discovery of Oxathiin fungicides was soon followed by confirmation of systemic activity of pyrimidines and benzimidazoles. A systemic fungicide is capable of managing a pathogen remote from the point of application. On the basis of chemical nature these fungicides are classified as follows
Common name Trade name Dosage Diseases managed ACYLALANINES
- Metalaxyl Ridomil 25 % WP, Apron 35 SD, Subdue, Ridomil MZ-72WP
3-6 g/Kg seed for seed treatment, 1 to 1.5 Kg a.i/ha for soil application, 0. to 0.2% for foliar spray
It is highly effective against Pythium, Phytophthora and many downy mildew fungi
- Benalaxyl Galben 25% WP and 5% G
0.1 to 0.2% for foliar spray, 1 to 1.5 Kg a.i/ha for soil application
Blue mold of tobacco, late blight of potato and tomato, downy mildew of grapevine AROMATIC HYDROCARBONS
- Chloroneb Demosan 0.2% for seed treatment
Seedling diseases of cotton , peanut, peas and cucurbits caused by species of Pythium, Phytophthora, Rhizoctonia and Sclerotium BENZIMIDAZOLES
- Carbendazim Bavistin 50WP, MBC, Derosol 60WP, Agrozim, Zoom
0.1% for foliar spray, 0.1% for soil drench, 0.25% for ST, 500-1000ppm for post-harvest dip of fruits
Effectively controls anthracnose, powdery mildews and rusts caused by various fungi. It is also used as a soil drench against wilt diseases and for post harvest treatment of fruits
- Benomyl Benlate 50WP 0.1 to 0.2% for ST, 50-60g/ L for foliar spray, 50-200ppm for soil drenching, 12-45 Kg a.i/ha for soil broadcast, 100- 500 ppm for post harvest fruit dip
Effective against powdery mildews of cucurbits, cereals and legumes. It is highly effective against diseases caused by the species of Rhizoctonia, Theilaviopsis and Cephalosporium. Benomyl has no effect against Oomycetes and some dark coloured fungi such as Alternaria and Helminthosporium
- Thiabendazole Mertect 60WP, Mycozol, Arbotect, Tecto and Storite
0.2 to 0.3% for spraying, 1000 ppm for fruit dip
Blue and green molds of citrus, loose smut of wheat, Tikka leaf spot of groundnut
PYRIMIDINES
- Fenarimol Rubigan 50% WP, 12%EC
2g/Kg seed as ST, 20 to 40 ml/100 liters of water for spraying
Powdery mildew of cucurbits, apple, mango, roses, grapes and ornamental crops
THIOPHANATES
- Thiophanate Topsin 50WP, Cercobin 50WP
0.1 to 0.2% for spraying
Powdery mildew of cuurbits and apple, club root of crucifers, rice blast 2.Thiophanate methyl
Topsin M 70WP, Cercobin M 70WP
0.1% for spraying
Blast and sheath blight of rice, sigatoka leaf spot of banana, powdery mildew of beans, chilli, peas and cucurbits TRIAZOLES
- Triadimefon Bayleton, Amiral 0.1 to 0.2% for spraying, 0.1% for seed treatment
Highly effective against powdery mildews and rusts of several crops. Effective against diseases caused by species of Erysiphe, Sphaerotheca, Puccinia, Uromyces, Phakopsora, Hemileia and Gymnosporangium
- Tricyclazole Beam 75WP, Baan 75WP, Trooper 75WP
2g/Kg seed for ST, 0.06% for spraying
Highly effective against blast of rice
- Bitertanol Baycor and Sibutol 0.05 to 0.1% for foliar spray
Powdery mildews and rusts of various crops, apple scab, Monilinia on fruit crops, late leaf spot of groundnut and sigatoka leaf spot of banana
- Hexaconazole Contaf 5%EC, Anvil
0.2% for spraying
Sheath blight of rice, powdery mildew and rust of apple, rust and tikka leaf spot of groundnut
- Propiconazole Tilt, 25% EC, Desmel
0.1% for foliar application
Sheath blight of rice, Sigatoka leaf spot of banana, brown rust of wheat
- Myclobutanil Systhane 10WP 0.1 to 0.2% for spraying
Apple scab, cedar apple rust and powdery mildew of apple STROBILURINS
- Azoxystrobin Amistar, Quadris 0.1% for spraying
Broad spectrum fungicide 2.Kresoxim methyl Ergon, Discus, Stroby
0.1% for spraying
Commonly used for control of ornamental diseases
CLASSIFICATION OF FUNGICIDES BASED ON METHOD OF APPLICATION
The fungicides can also be classified based on the nature of their use in managing the diseases.
- Seed protectants: Ex. Captan, thiram, carbendazim, carboxin etc.
- Soil fungicides (preplant): Ex. Bordeaux mixture, copper oxy chloride, Chloropicrin, Formaldehyde, Vapam, etc.
- Soil fungicides: Ex. Bordeaux mixture, copper oxy chloride, Captan, PCNB, thiram etc.
- Foliage and blossom: Ex. Capton, ferbam, zineb, mancozeb, chlorothalonil etc.
- Fruit protectants: Eg. Captan, maneb, carbendazim, mancozeb etc.
- Eradicants: EX. Lime sulphur
- Tree wound dressers: Ex. Boreaux paste, chaubattia paste, etc.
- General purpose sprays and dust formulations.
HOST PLANT RESISTANCE (IMMUNIZATION)
Disease resistance : It is the ability of a plant to overcome completely or in some degree the effect of a pathogen or damaging factor.
Susceptibility : The inability of a plant to resist the effect of a pathogen or other damaging factor.
Advantages of resistant varieties :
- Resistant varieties can be the most simple, practical, effective and economical method of plant disease management.
- They not only ensure protection against plant diseases but also save the time, energy and money spent on other measures of control
- Resistant varieties, if evolved can be the only practical method of control of diseases such as wilts, viral diseases, rusts, etc.
- They are non-toxic to human beings, animals and wild life and do not pollute the environment
- They are effective only against the target organisms, whereas, chemical methods are not only effective against target organisms but also effective against non-target organisms.
- The resistance gene, once introduced, is inherited and therefore permanent at no extra cost.
Disadvantages :
- Breeding of resistant varieties is a slow and expensive process
- Resistance of the cultivar may be broken down with the evolution of the pathogen
Types of resistance :
- Vertical resistance : When a variety is more resistant to some races of the pathogen than others, the resistance is called vertical resistance (race-specific resistance, qualitative resistance, discriminatory resistance). Vertical resistance is usually governed by single gene and is unstable.
- Horizontal resistance : When the resistance is uniformly spread against all the races of a pathogen, then it is called horizontal/generalized/non-specific/field/qualitative resistance. Horizontal resistance is usually governed by several genes and is more stable.
- Monogenic resistance : When the defense mechanism is controlled by a single gene pair , it is called monogenic resistance.
- Oligogenic resistance : when the defense mechanism is governed by a few gene pairs , it is called oligogenic resistance.
- Polygenic resistance : When the defense mechanism is controlled by many genes or more groups of supplementary genes, it is called polygenic resistance.
Cross protection: The phenomenon in which plant tissues infected with mild strain of a virus are protected from infection by other severe strains of the same virus. This strategy is used in the management of severe strains of Citrus Tristeza virus
