Plant disease management – Part 1

June 6, 2012
By Krishiworld

QUARANTINE :- The best way to control diseases is to exclude them from the area of sphere in which the host plants are being known. This method of exclusion enforced through certain legal measures is commonly known as quarantine. In India, Destructive Insects & Pests Act, was enacted in 1914. Directorate of Plant Protection & Quarantine was established in Delhi. 

Quarantine stations have been established in airports, seaports & selected railway stations. Plants & Plant Products to pass through these quarantines should be accompanied by a phytosanitary certificate, as per international convention, issued by the competent authority of the exporting country. To export the plants & plant Products from India, State Plant Pathologists have been empowered to issue phytosanitary certificates. 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.

By proper Cultural Practices many diseases can be controlled

  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)
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