Studies on the problems of citrus nematode in orchards and nurseries of mandarin orange in darjeeling hills and their management

The problems of citrus nematode (Tylenchulus semipenetrans Cobb) in orchards and nurseries of mandarin orange in Darjeeling hills have been studies during 1988 to 1991. This nematode could be isolated from the infested roots and root zone soil and the slow decline symptoms could be reproduced in orange through seedling soil inoculation. Citrus nematode occured in all the orchards surveyed but its incidence differed with respect to the season of observation and physiological condition of the plants. The population was high during March-April and low during November-December under Darjeeling condition. All the common citrus species tested excluding trifoliate orange (Poncirus trifoliata) were found to be susceptible to this nematode. Infested seedlings have been found to be an important means of spread which could be controlled by treating the roots with 200 ppm of thimet (10 g) or nemacur (10 g) for 30 minutes. Nematode population in an orchard may be reduced by applying furadan (3g) or thimet at the rate of 100 g/tree twice in a year Growing annuals, particularly cabbage, cauliower, aster, zinnia and marigold etc. in the orchards reduced the nematode population both on the feeder roots and in rootzone soil.