Plant disease management – Part 2

June 7, 2012
By Krishiworld


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 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.


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.


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.

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