RICE RATOONING - IRRI books - International Rice Research Institute

DISEASE AND INSECT PESTS IN RICE RATOONING SYSTEMS 235incidence in the ratoon. The infected plant shows brown or black necrotic area onthe outermost leaf sheath, leading to withering and breaking up of main culm, anddeath. Abnormal tillers produced at the plant base after infection produce nothing; ifany ears are produced, they have a high proportion of light grains. Sprayingedifenphos benomyl, or blasticidin-S might control the disease, although fungicidesare not widely used to control this disease (5). Proper management, such as optimumcutting height, may also reduce its incidence.Udbatta caused by Ephelis oryzae, a systemic infection that is increasing inhilly areas of Karnataka, is important in ratoon cropping. Infected main cropstubble cause 100% loss in ratooned plants. Infected plants produce dirty colored,hard cylindrical spikes instead of normal ears. Careful roguing to uproot udbattainfectedplants in the main crop before cutting is a prerequisite to ratooning.Other minor diseases of rice (sheath rot, caused by Rhizoctonia solani; falsesmut, by Ustilaginoidea virens; kernel smut, by Neovossia barclayana; foot rot orbakanae, by Fusarium moniliforme; etc.) are of little importance on ratoon cropsduring the cropping season in Karnataka.Diseases caused by nematodesNematode diseases have not been reported on ratoon crops. Burning rice stubble hasbeen recommended, because rice leaf nematode caused by Aphelenchoides besseyisurvives on them. Survival of rice stem nematode caused by Ditylenchus angustuson self-sown rice plants, stubble, and ratoons left in the main field after harvest hasbeen reported (5). This indicates their possible occurrence on the ratoon crop inendemic areas, although such reports are not available. Root-knot nematode causedby Meloidogyne spp., rice cyst nematode caused by Heterodera oryzae, rice root orburrowing nematodes caused by Hirschmanniella spp., rice stunt nematode causedby Tylenchorhynchus martini, and rice nematode caused by Macroposthoniaonoensis are other nematodes reported. Their importance, if any, on ratoon crops inpotentially infected areas and studies of control methods may be worthwhile.Diseases caused by viruses and mycoplasma-like organismsSeventeen diseases have been reported to be caused by viruses and two diseases byMLOs have been reported on rice (15). Six of them: tungro, grassy stunt, raggedstunt, chlorotic streak, necrosis, and yellow dwarf, are occurring in India. All of theviruses and MLOs pose a threat to ratoon rice cultivation. They are normallyunnoticed or found only in late stages of the main crop, when little sign of disease orlatent infection is noticed. But regrowth from such stubble will show typicalsymptoms, causing total failure of the ratoon crop.Yellow dwarf appeared in an epidemic form in Japan, infecting 70-80% of thehills and causing 50% yield reduction (12). In India, yellow dwarf was observed up to27.3% on the main crop (var. MR249) (18). Distinct chlorotic symptoms appear onratoon growth, which produces numerous, yellow, stunted tillers from the basalnodes. They normally do not flower. Yellow dwarf is transmitted by Nephotettixspecies (green leafhoppers). N. virescens, N. cincticeps, and N. nigropictus are themore efficient vectors of the disease.