Eggplant Integrated Pest Management AN ECOLOGICAL GUIDE

___________________________________________________________________________________Major Agronomic Practices3.10.1.1 Burning organic material on the soilA common method of soil sterilization is heating up the soil. The high temperature will cause the death ofmany micro-organisms, including pathogens in the top soil and insect pest with soil-dwelling stages, suchas cutworms. In Bangladesh and India for example, soil sterilization is commonly practiced by burningstraw, or dry grass, leaves or waste material on the nursery beds before sowing. It should be noted thatstraw burns very quickly and the heat does not penetrate deep enough into the soil. This may result inonly a very thin top layer of the soil being sterilized. A substantial amount of slow-burning but hightemperatureoutput material would be required on the soil, e.g. wood rather than grass (Bridge, 1996).Rice husk is preferred to straw because it burns slower and the heat penetrates deeper into the soil,resulting in better sterilization.In Bangladesh, Choudhury and Hoque (1982) demonstrated that by burning a 5-cm thick layer of ricehusks (burnt in 90 min) and a 5-cm thick layer of sawdust (burnt in 60 min) on the surface of vegetableseed beds, rootknot nematode galls on the following crop of eggplant were reduced to 23 and 37%,respectively, of the number of root galls in non-treated seed beds. A 15-cm thick layer of rice straw (burntin 20 min) however only reduced galling to 50% of the control plots.Soil from fire placeAnother example of an alternative method of soil sterilization came from Bangladesh, where afarmer used the soil from his fire place to prepare a nursery. This soil had been heated severaltimes over a long period for cooking activities. The heat had killed pathogens in the soil. It wouldbe advisable to mix the soil with compost before sowing seed (pers. comm. farmer Chittagong,Bangladesh, 1998).3.10.1.2 SolarizationAnother soil sterilization method is solarization - with help of the sun's energy. Solarization of seedbedscan control soil-borne diseases, weed seeds and some nematodes including rootknot nematodes.However, not all pests are controlled.To solarize soil, the soil is covered with clear polythene/plastic sheets. The best time is during the hotseason, when there is plenty of sun. The sun heats up the soil through the clear plastic, and the plasticsheet keeps the heat inside the soil. Usually, the sheets should be left on the soil for at least 4 weeks,depending on the season (hours of sunshine and temperature) and the area (lowland or highlands). Thesoil should be moist before the plastic sheets are placed and the sheets should be properly fixed on thesides to avoid loosing heat. Also check the polythene sheets for holes and repair them where necessary.Ploughing the soil before applying the plastic sheets seems to help to break up crop left-overs and bringnematodes to the surface so the heat can destroy them. Allow the soil to cool down for at least a fewdays before sowing seed.plastic sheet, fixedwith soil at the bordersSolarization: the sun heats up the soil under the plastic sheet and kills insects, diseases and some weeds.Solarization alternative from Jessore, BangladeshA farmer from Jessore had trouble with damping-off disease in his soil. To raise seedlings in a nursery,he took soil, mixed it with cow dung and some water and put this in plastic bags. He placed the bags inthe full sun, some on top of his roof, and left them for about 2 weeks. Then, he used the soil to preparea raised nursery bed in which the seed were sown. He reported no further trouble with damping-off!(Pers. comm. Mr. Yousuf, Jessore, Bangladesh, 1998)33Eggplant Ecological Guide