RICE RATOONING - IRRI books - International Rice Research Institute

DISEASE AND INSECT PESTS IN RICE RATOONING SYSTEMS 237suitable systemic insecticides, such as dimethoate or phosphamidon, immediatelyafter the main crop harvest may take care of the insect vectors at the initial stages ofratoon growth and reduce the incidence of these diseases. All these aspects need to bestudied.INSECT PESTSInsect pests on the ratoon crop have been studied in relation to the main crop atMudigere, Karnataka (6). On Intan paddy, higher incidences of orange leafhopperThaia subrufa, green leafhoppers Nephotettix spp., and brown planthopperNilaparvata lugens are observed on the ratoon crop than on the main crop. Otherinsects present on both main and ratoon crops are whorl maggot Hydrellia griseola,paddy gall midge Orseolia oryzae, leaffolder Cnaphalocrocis medinalis, thripsBaliothrips biformis, and stem borers Tryporyza incertulas and T. innotata.The leafhoppers do not cause much damage in the regular season, buthopperburn damage is enormous November-March. The orange-headed leafhopperseems to be specific to the hilly region of Karnataka, with severe damage November-May (10). This pest has not been observed around Bangalore, perhaps because ofseasonal conditions in that region. Stem borers produce deadheart symptoms duringearly growth and white ears during flowering, causing considerable damage to therice crop. Leaf roller-infested plants appear scorched and sickly; high infestationleads to severe yield losses.Because pest populations start building up in a ratoon crop, without plantprotection they could migrate to the transplanted summer crop and cause severedamage. Population in the initial stage of buildup on the ratoon crop must beeffectively controlled. Applying suitable granular insecticides, such as carbofuran,phorate, and sevin (granular), or spraying systemic insecticides, such as dimethoateor phosphamidon, immediately after the main crop is cut may be sufficient toeliminate all insect pests as well as disease vectors in early stages of the ratoon crop.One more spraying of dimethoate or phosphamidon at the flag leaf stage may besufficient to reduce insect pests at later stages of the ratoon crop, especially stemborers and leaf rollers. Cultural practices such as removing all the debris around theratoon crop may help in controlling not only insect pests and vectors, but alsodiseases by reducing the primary sources of inoculum.However, research on important diseases and insect pests occurring mainly onthe ratoon crop and economic control measures is needed. Breeding work also mustbe intensified to develop good-ratooning varieties with resistance to the diseasescaused by viruses and MLOs.