Disease management

[kheteshwar borawat]

Disease management

Control of Diseases

In India, Destructive Insects & Pests Act, was enacted in 1914. Directorate of Plant Protection & Quarantine was established in Delhi. Quarantine is the best way to control diseases. It aims to exclude diseased crops from the area of sphere in which the host plants are being known. Some of the plant materials have been totally banned for import into India irrespective of any certificate. Potatoes can not be imported to India from any wart disease and/ or golden nematode infested areas. Unginned cotton can not be imported. Sugarcane cuttings from Australia, Fiji & Philippines cannot be imported. Import of cocoa from Africa & Sri Lanka is totally banned. Rubber plant & seeds from South America & West Indies & Sunflower seeds from Argentina & Peru are totally banned. Within India, Domestic quarantines have also been established.

Ways of disease management

Cultural practices

1. Seeds: Loose smut of wheat (ustilago tritici), black arm of cotton (xanthomonas compestris Pv. Mulvacearum ) and leaf crinkle of blackgram (virus) are introduced into the field through seeds. Hence, the infected seed should not be used for sowing.
2. Vegetative Propagating Material: Banana suckers may carry the bunchy top virus, hence suckers from diseased areas should not be used. Sugarcane setts may carry red rot pathogen (colletrichum falcatum). Hence sugarcane setts from diseased areas should not be used for planting.
3. Irrigation & Drainage Water: Bacterial blight of rice (xanthomonas compesteris pv.oryzae) spreads mostly through irrigation & drainage water. Hence, care should be taken not to irrigate a healthy filed using drainage water from an infected field.
4. Plant debris: Some of the Pathogens survive in Plant debris e.g. stem rot of rice (scterotium oryzae & black arm of cotton (x.compestris pv. malvacearum) Hence plant debris should be burnt or removed.
5. Equipment & Men: Pruning implements, intercultivators, etc, may carry some pathogens e.g. tobacco mosaic virus in tobacco. Field workers also may carry the virus from infected field to the healthy field. Hence proper sanitation is needed.
6. Weeds: Weeds serve as alternate hosts for many Pathogens e.g. rice tungro virus, rice blast etc. Hence clean cultivation is essential for control of diseases.
7. Volunteer Plant : Self-sown volunteer plants may carry infection, which may serve, as source of infection for the succeeding crop. E.g. cotton black arm. Volunteer Plants should be destroyed.
8. Ratoons : Ratoon Crops normally carry many Pathogens e.g. sugarcane grassy stunt. Ratoon crops should be avoided as far as possible.
9. Rouging infested Plants : The infected plants should be rouged out to reduce the inoculum in the field. Rouging infected Plants can reduce yellow mosaic of green gram.
10. Pruning of infected twigs & branches : Pruning of citrus canker affected branches reduces the disease incidence.
11. Solar Heating : When the soil is covered with Polythene sheets during hot seasons, soil temperature increased & eliminated verticillium deuliage & fusarium oxysporium f.sp. lycopersici in tomato field.
12. Flooding the field: Flooding the field for long time can control Fusarium wilt of banana.
13. Fallowing By fallowing, F.oxysporium specific strains can be reduced, as they do not survive in soil for long time.
14. Date of sowing: Early sowing of Pearl millet will reduce the ergot disease. Avoiding wet seasons for planting of rice will eliminate rice blast.
15. Avoidance of monoculture: Continuous cultivation of rice crop may result in the appearance of new pathotypes of Puricullaria oryzae, the rice blast pathogen.
16. Multiple Cropping: Taller crops can be sown to protect a crop of lesser height from virus vectors.
17. Intercropping Intercrops should be properly chosen so that all the crops should not have any common pathogen.
18. Trap crop: Tagets is a trap crop for many nematodes & can be grown to reduce nematode infection.
19. Tillage: Ploughing of rice residue to a depth of 25 to 30 cm renders a high Percentage of inoculum of sclerotium oryzae unavailable for infection of rice subsequently sown with flooding.
20. Soil Amendment: Potato back skurf (Rhizoctonia Solani) is less in soil amended with wheat straw. Lucerne meal & barley straw reduce root rot of cotton caused by Macrophomina Phaseolina.
21. Seed rate & Spacing Closer spacing favours many air-borne diseases because of high humidity in the crop canopy. Tikka leaf spot of groundnut (cercospora arachidis) is more in dense canopy. Damping off caused by Pythium & Phytophthora increases in crops when higher seed rate was used.
22. Irrigation: Maintaining soil water near field capacity during tuber formation prevents potato scab (streptomyces scabies). High soil moisture increases antagonistic bacteria population.
23. Nitrogenous Fertilizers: Increased application of nitrogen increases many diseases. Rice blast becomes severe in nitrogen-applied fields. Split application reduces blast & bacterial blight of rice. Contrarily late application of nitrogen increases wheat leaf blotch (septoria nodorum) & powdery mildew (Erysiphie graminis) Wilts (Fusarium spp.) & rots ( Rhizoctonia spp.) are favored by ammoniacal nitrogen while verticillium wilts & root rots due to pythium spp. are favored by nitrate nitrogen.
24. Phosphorus : Repeated application of prophetic fertilizers delays the onset & lessens the severity of take-all disease of barley.
25. Potassium : Potassium application reduces the disease incidence in many cases probably by increasing Phenolics synthesis in plants.
26. Calcium: Calcium application reduces bean root rot caused by Rhizoctonia Solani probably by altering pectin metabolism of the host.
27. Molybdenum: Application of molybdenum reduces infection of potato tubers by Phytophthora infestans & also diminishes incidence of Ascohyta blight on beans & Peas.
28. Manganese: Manganese reduces late blight of Potato.
29. Iron: Ferric Chloride controls rice brown spot.
30. Silicon: Silicon application reduces rice blast (Pyricularia oryzae)

Use of Resistant Cultivatars

Several types of resistant cultivars are now available. When a variety is more resistant to some race of pathogen than to others, the resistance is called vertical. Vertical resistance can be preferred against pathogens, which do not have many races, or in the host, which is not cultivated throughout the year. When host resistance is equally effective against all races of pathogen- it is termed horizontal. Horizontal resistance will be more useful in subsistence agriculture. Judicial management of diseases by employing different resistant varieties is the best & cheap method of disease control.

Biological Control

Biological control of disease includes management of diseases by organisms including plants, but excluding man. Biological control can be achieved by –
(i) Using micro organisms
(ii) Changing growth conditions of the plants (cultural practices); and
(iii) Using resistant varieties
Important Biocontrol Microbial agents: -
1. Fungi –
(a) Trichoderma spp. against damping off of peas, tomato & tobacco, root rot of groundnut.
(b) Gliocladium virens – Pythium, Sclerotium & rhizoctonia diseases.
2. Bacteria – Pseudomonas Fluorescens & P.Putida control soft rot of Potato.

Fungicides & Antibiotics

Definitions –
1. Fungicide - is a chemical, which is capable of killing fungi.
2. Antibiotic- is a chemical produced by a microorganism, which is inhibitory to other organisms. Fungicides can be classified as protectants, eradicants & systemic fungicides.
a. Protectant- Fungicide which is effective only if applied prior to fungal infection is called Protectant. Example – Mancozeb, Zineb.
b. Eradicant – is the one, which removes fungi from an infection court. An Eradicant can penetrate the host tissues to a limited extent & eliminate an established infection. Example – Lime Sulpher.
c. Systemic Fungicides- Systemic fungicides are the compounds, which are transported over a considerable distance in plant system after-penetration. They kill fungi, which are found remote from the point of application.

(I) Sulphur Fungicides

a) Inorganic Sulpher fungicides - includes elemental Sulpher, wettable Sulpher & lime Sulpher. Sulpher fungicides effectively control powdery mildew of different crops such as chilli, okra, grape, rubber, mango, citrus, black gram & green gram. Sulpher controls tikka leaf spot of groundnut & Diplocapron black spot of rose. Sulpher dust is used as seed treatment also.
b) Organic Sulpher fungicides- Dithiocarba mates are the organic Sulpher fungicides. They are divided into-
(i) Dialkyldithiocarbamtes- Thiram, Ziram & ferban & Ziram is used as Protectant & sprayed before the outbreak of the disease. It controls early blight of potato & tomato and anthracnose disease of cucurbits & beans. Thiram is commonly used for seed treatment. Thiram seed treatment controls seed-borne pathogens as well as soil born pathogens. It controls seed borne infection of colletotrichum capsici of chilli, root rot of groundnut, sorghum grain smut & Helminthosporium leaf spot of rice. As seed treatment it controls soil-borne infection of Phthium spp. of tomato, tobacco & brinjal (Damping off) Rhizoctonia solani of cotton & Sheath blight of rice. Ferban control diseases of apple. It controls leaf spot of banana, leaf mould of tomato & leaf spot of coffee.
(ii) Monoalkyldithio carbamates- maneb, Zineb, Mancozeb, vapam & nabam. Zineb controls anthracnose disease of bean, chilli, & cucurbits, rust disease of wheat, sorghum & bajra, downy mildew of grapevine, cucurbits, Onion & cabbage, cercospora leaf spot of groundnut, cabbage, cauliflower, Alternaria leaf spot of potato, tomato singer. Mancozeb is widely used for the control of late blight of potato, cercospora leaf spot of groundnut, cucurbits & sugar beet. Helminthosporium leaf spot of rice, ragi, maize & sorghum, downy mildew of grapevine & tobacco, rust disease of wheat groundnut, bajra & sorghum, Alternaria leaf spot of ginger, potato, tomato & wheat anthracnose of chilli, grapevine, sorghum, bean & cucurbits.
Vapam controls cotton wilt & damping off of papaya, tobacco & tomato. It controls nematodes also.

(II) Copper Fungicides

(a) Copper Sulphate Preparations – It include Bordeaux mixture, Bordeaux Paste, Burgundy mixture, & chestnut compound. Bordeaux mixture is highly effective against late blight of potato, downy mildew of grapevine, coffee rust, betel vine wilt, pepper wilt, tomato early & late blights & coconut will & bud rot.
(b) Copper Carbonate Preparations- It controls many fungal diseases of apple, pear, peach, plums & apricot.
c) Copper Oxychloride Preparations – Some formulations available in the market are Fytolan, Blue copper, Blitox etc. They are generally effective against all diseases against which Bordeaux mixture has been found effective.

(III) Mercury Fungicides

Various mercury fungicides sold in the market are ceresan, aretan, agallol, wet ceresan, Dry ceresan etc. They are effective as seed treatment.
IV Heterocylic nitrogen compounds-
a) Captan- It is commercially marketed as Captan, orthocide, vancide etc. It is Protectant fungicide. It controls maize helminthosporiose, chilli fruit rot & apple scab. It is mostly used as seed treatment.
b) Folpet – It is commercially marketed as Phaltan. It controls rose black spot & apple scab.
(c) Captofol – It is marketed as Difolotan, Foltaf etc.
It effectively controls sheath rot of rice & mango anthracnose.
V) Quinone Fungicides-
a) Chloranil – It is commercially marketed as spergon. It is good seed dressing fungicide. It controls grain smut of sorghum & damping off of beans & cotton.
b) Dichlone- The commercial name of the fungicide is phygon. It controls peach leaf curl, apple scab & bean anthracnose.

(IV) Miscellaneous Fungicides

a) Quintozene - Commercial names of the fungicide are Brassicol, Terraclor, PCNB & Tritisan. It is used to control soil borne pathogens. It is effective against Rhizoctonia Solani, Macrophomina Phaseolina & Sclerotiana Sclerotiorum.
b) Dinocap - It is marketed in the name of karthane, Arathane, Mildex etc. Dinocap is effective in controlling powdery mildews.
c) Fenaminsosulph- it is commercially known as Dexon. It is highly effective against phycomycetes like pythium phytophthora & Aphanomyces.
d) Dicloran_ Its trade name is Botran. It controls Botrytis infection in several crops.
e) Chlorothalonil- It is marketed as Daconil & Kavach. It controls both tikka leaf spot & rust disease of groundnut & betelvine wilt.

(V) Systemic Fungicides

Some of the systemic fungicides are-
a) Carbendazim – It is marketed as Bavistin, Derosal, B-Sten etc. It controls Powdery Mildews, smut diseases & bunts.
b) Benomyl- Benomyl is effective against Fusarium , Rhizoctonia, Macrophomina, Cercospora, Colletotrichum, Puricularia, Verticillium, Phomopsis, Septoria, Erysiphe, Plasmodiophora, Botrytis, Ustilago, Urocystis & Tilletia Spp.
c) Thiabendazole – It is commercially available as Tecto & Mertect. It controls wheat bunt.
d) Carboxin- it is commercially available as vitavax. It is the most effective fungicide to control internally seed borne loose smuts of cereals.
e) Oxycarboxin- it is commercially marketed as Plantvax. It is specifically effective against rust pathogens.
f) Pyracarbolid- it is commercially available as sicarol. It is effective against rust & smut & Rhizoctonia Spp.
g) Metalaxyl- it is marketed as Ridomil & Apron. Metalaxyl is highly effective against phycomyces fungi like Phytophthrora, Pythium, Scierospora, Pseudopernospora, Plasmopara, Sclerophthora & Albugo.
h) Tride morph- its trade name is calixin. It is mainly used against powdery mildews as foliar sprays
i) Pyroquilon- it is commercially available as Fongorene. It effectively controls rice blast.
j) Kitazin- it is commercially marketed as Kitazin. It is highly effective against rice blast.
k) Tricyclazole – it is commercially marketed as Beam. It is highly specific for the control of rice blast.
l) Probenazole- its commercial name is oryzemate. It is also specific against rice blast.
m) Triadimefon- it is commercially market as Bayleton. It is highly effective against powdery mildews. It also controls rust diseases.
n) Biloxazole- it is marketed as Baycor. It is effective against cercospora diseases & rusts.
o) Triademenol- The commercial name of the fungicide is Bayton. As seed treatment it controls smut & powdery mildews.

Antibiotics

(i) Aureofungin sol- It is a broad spectrum antibiotic produced by streptoverticillium cinnamomeus var. terricola. Aureofungin is effective only when it is mixed with copper sulphate. It controls Than javur will of coconut, citrus gummosis, chillies powdery mildew & grapes downy mildew.
(ii) Streptomycin- it is produced by streptomyces griseus. It controls bacterial diseases viz. Citrus canker, black arm of cotton & rice bacterial blight.
(iii) Tetracycline- It is produced by streptomyces sp. and effective in controlling mycoplasma diseases like sandal spike, brinjal little leaf & gingelly phyllody.

Biotechnology

Plant Pathology has entered into a new era. Plant Pathologists have now learnt to use the modern tools of genetic engineering & tissue culture in management of plant disease. It is now possible to isolate particular gene from one organism, insert them into the genome of another organism & make them to express at right time. This technology is known as 'Genetic Engineering'. Cells of plants can be cultured in special nutrient medium & whole plant can be regenerated from cultured cells. This technique of growing plants in vitro is called 'Tissue Culture'. The biological technique through which the laboratory experiments are converted into practical utility materials, under field conditions is called 'Biotechnology'.

Integration of plant disease management practices

The four basic requirements for management of plant diseases are clean & healthy seeds, clean field or pathogen free soil, prevention of entry of and infection by a pathogen in a standing crop & precautions during harvesting & storage of the produce. An ideal schedule for controlling a disease is to integrate measures covering these four requirements. In an integrated diseased management programme in an annual crop (potato, cereals etc.) the first step is the choice of healthy seed of a resistant variety. In potato, the seed tubers carry pathogens of late blight of potato, bacterial wilt, and almost all the viruses. In wheat, seed is the only source of loose smut. In sugarcane, seed setts carry the red rot, wilt & smut pathogens and also the viruses. The healthy clean seed can be obtained as a certified seed from a reliable agency. The next step is to treat the seed chemically if the supplier has not done the same. The healthy, pathogen free seed is then planted in relatively clean field. In potato, the field should be free from old crop debris. If root knot nematodes are a problem, furrow application of a systemic granular nematicide should be given. Crop rotation is another precaution. During growth of the crop periodical rouging of diseased plants, if any, should be done. The inoculum of a pathogen may arrive from external sources. This inoculum should be prevented from causing infection by sprays of suitable chemicals. At the time of harvest, care should be taken, to discard diseased plants, do the harvesting in a clean weather, and store the produce in proper storage conditions.

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Have a lot of fun and success.
yours kheteshwar
always with you...

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