Abstract
Studies on the rhizome damage of ginger by pests and their management were carried out in the field and laboratory during April 2006 to December 2008. The level of rhizome damage in the field was estimated through farmer's interview using structured questionnaire and direct observation. Both farmer's opinion and direct observation indicated the occurrence of crop damage throughout the growing stages but the extent of damage was high at rhizome forming stage showing the maximum of 11.21% and 17.41% in hill tract, 23.55% and 35.78% in Rangpur during 2006 and 2007, respectively. The farmers of both the regions adopted various practices to manage the problem. Field and laboratory studies showed that both fungal and bacterial pathogens were primarily responsible for rhizome damage while the rhizome fly, Mimegralla coeruleifrons Macquart appeared to be the secondary causal agent. The maggots of the fly were found only in the fungus infected rhizomes. Two groups of pathogen caused a yield loss of 60% while the presence of rhizome fly along with pathogens caused 62.8% yield loss. The ginger plant damage by the pests became visible in June and reached its peak in September. The rhizome fly required about two and half months to reach its peak immature population in the field. The immature fly population increased with higher intensity of plant damage caused by the fungal pathogen. An average of 12 maggots and pupa were found in severely damaged rhizome. A female fly laid about 120.25 eggs in first generation and 80.25 eggs in second generation either singly or in batch on rotten rhizomes. The duration of different life stages varied significantly in two successive generations. The average incubation period, larval period, pupal period, adult male longevity and female longevity in two successive generations were 4.5 days, 31.75 days, 5.75 days, 6 days and 12.5 days, respectively. The dark-brown adult fly with transparent wings having three ashy spots emerged from the pupa after 4.25 to 7.25 days. The removal of seed rhizome commonly called pelai harvest after 107 days of plantation caused 2 to 3 folds higher plant damage than the normal harvest and a maximum of 52.9% yield loss. Out of 10 ginger germplasms tested, only the line G 001 was found to be less susceptible to pest attack and showed significantly higher yield. Pre-sowing soil application of neem oil cake @ 400 kg ha' in combination with Ridomil Gold MZ 68 WG @ 7 kg ha' and basal application of the Ridomil Gold @ 3.5 kg ha' at 4 weeks interval commencing from the first occurrence of plant damage were found as the most effective management options of the pests. Economic analysis ranked the pest management effectiveness as: pre-sowing application of Ridomil Gold @ 7 kg ha1> Lorsban 15 G @ 15 kg ha' with Ridomil Gold @ 7 kg ha'> Neem Oil Cake @400 kg ha when the treatments were supplemented with the application of Ridomil Gold @ 3.5 kg ha1 after the first occurrence of plant damage.