RICE RATOONING - IRRI books - International Rice Research Institute

YELLOW DWARF DISEASE IN RATOON RICE 223Tabla 3. Yellow dwarf incidence in ratoon hybrid rices, 1985-86.Variety/selectionP203A/lntan MutantIR29723-243-3-2-1Wei-You 64IR46830A/13292-5-2MS 577A/lntan MahsuriP203A/lntan MahsuriIR21845-90-3A/IR5497A/Milyang 54Iri 356A/MilyangIR46828A/Milyang 54577A/lntan Mutant 1IR46831A/IR 54% incidence0.000.160.160.170.300.3 10.460.470.630.791.09CONTROLThe occurrence of yellow dwarf in the field was decreased to some extent by applyingcarbaryl (1-naphthyl N-methylcarbamate) or vamidothion (N-methyl O,O-dimethyltriolophosphoryl-5-thio-3-methyl-2-valeramide)twice during the rice nurseryperiod (29). Malathion, carbaryl dust, and other chemicals were used, usually soonafter transplanting, to kill overwintering insects (7, 27).Carbaryl (1-naphthyl N-methylcarbamate) when applied to soil at 3 kg ai/ hacontrolled Nephotettix spp. effectively (14). Seed treatment with carbofuran ormethomyl or phorate or propoxur protected rice seedlings from the leafhoppers(26, 45).Leafhopper mortality was higher in plots treated with phosphamidon (0.03%),carbofuran (0.04%), dimethoate (0.0125%), and demeton-S-methyl (0.025%) andyellow dwarf incidence was reduced from 5.80 to 0.94% (31).CONCLUSIONSIn recent years ratoon cropping of rice has been practiced in parts of Karnataka (20,23, 46). There is a great potential for adopting rice ratoon cropping in parts of thecountry. Yellow dwarf might become a limiting factor for raising a ratoon rice cropbecause the disease is predominant in the ratoon crop. Only tolerant varieties shouldbe recommended wherever ratooning is practiced. Also, resistant varieties shouldinvariably be used in future breeding programs to evolve resistant types suitable forratoon cropping.After the main crop is harvested, leafhoppers persist on the stubble. Becausethe initial inoculum is available, the disease spreads much faster in the ratoon crop.A week or 10 d after main crop harvest, it is important to spray the ratoon crop withinsecticides to kill leafhoppers to prevent further spread of the disease.