Overview :
Seed is the mother of the plant. Healthy seeds will produce a healthy plant and vice versa. On the seed surface and inside the seeds of field crops and vegetables, a number of disease causing pathogen are present. These micro-organisms are present in soil also and cause diseases. These seed and soil borne diseases may destroy the seeds affecting its germination and also infest the growing seedlings and the plants, resulting in poor plant population and unhealthy crop and finally reduced yield. Hence, to get a healthy crop, the seed should be treated with seed treatment chemicals as per recommendation of the scientists/government.
The seed treatment concept in India is still at infant stage. It is a common practice amongst farmers to use their own seeds and largely without any seed treatment.
Several organisms like Fungi, Bacteria, Virus, Phytoplasma, Protozoa and Nematodes cause internal and external deformities in plants, which is referred as disease. The disease causing organisms produce definite symptoms in crop plants/seeds. The diseased crop does not attain its natural growth, thereby adversely affecting the crop yields. The soil and seeds are the main source of disease infection in crops. Apart from these, air, water and other sources also help in the spread of the diseases. The organism of seed borne diseases remains dormant inside/surface of the seed and infects the plant at any stage of the crop i.e. from germination to seed formation. The Smut and Karnal bunt of wheat, Collar rot of groundnut, green ear head of Pearl millet etc. are examples of seed borne diseases. The causal organisms of some of the diseases remain in soil and in the presence of favourable conditions, infect the seed and the germinating seedlings. The Pythium, Sclerotium, Rhizoctonia, Microphomina are the fungi which cause soil borne diseases in pulses and other crops. The spread of diseases in standing crops is also facilitated by air, water and other sources.
The chemical compounds or bio-agents used to kill or inhibit the fungi or fungal spores are termed as Fungicides.
Classification of Fungicides :
Fungicides have been grouped into different categories on the basis of their chemical nature, and mobility in plants, as below:
Chemical Nature
- Inorganic
- - Sulphur
- Dithiocarbamate
- - Thiram, Ziram, Ferbam Mancozeb, Nabam
- Copper based
- - Copper oxychloride, Copper hydroxide
- Carbonic mercury
- - Ethyl mercuric chloride, Phenyl mercuric oxide
- Quinones
- - Chloranil, Dichlore
- Heterocyclic nitrogen
- - Captan, Folpet, Captafol
- Benzimidazole
- - Carbendazim, Benomyl, Thiabendazole
- Thiophanate
- - Thiophanateethyl, Thiophanatemethyl
- Oxathin
- - Carboxin, Oxycarboxin,
- Phenylamides
- - Metalaxyl, Oxadixyl, Benalaxyl
- Triazoles
- - Propiconazole, Flusilazole, Hexaconazole, Tricyclazole, Myclobutanil, Penconozole
- Morpholine
- - Tridemorph, Dodemorph
- Organophosphorus
- - Kitazin, Kitazin P., Fosetyl AL
- Acetamides
- - Cymoxanil, Chlorothalonil
- Others
- - Dinocap, Chinomethionate
Mobility
- Contact Fungicides :
- These fungicides control the diseases by contact action and are not absorbed by the plant tissues and remain on the surface of the plant. Repeated application is needed to control new fungi growth, eg. Mancozeb, Thiram etc.
- Systemic Fungicides :
- These fungicides are absorbed by the plant tissues and translocated in whole plant, e.g. Hexaconazole, Flusilazole, Carbendazim
- Translaminar Fungicides :
- The fungicides redistributed from upper leaf surface to lower unsprayed leaf surface, e.g. Trifloxystrobin, Azoxystrobin