Ratu Kinley & Chinta Mani Dhimal
In Bhutan, litchi production is constrained by insect pest damage. Among insect pests, the litchi fruit and shoot borer (Conopomorpha sinensis Bradley) is an emerging pest of economic importance in the subtropical regions of Bhutan. Up until now, there is documented research on its biology and management in Bhutan. Therefore, this study was undertaken to study the efficacy of two different management methods against litchi fruit borer infestation in three litchi varieties (Bhur litchi 1, Bhur litchi 2 & Hong houy). The management methods consisted of three treatments; T1-Azadirachtin followed by Imidacloprid, Azadirachtin and Cypermethrin; T2-Azadirachtin followed by Imidacloprid, Azadirachtin and Azadirachtin; T3-Untreated control. The result showed that the fruit infestation at harvest was significantly lower in management method T1 (34.74%) as compared to T2 (78.07%) and untreated control (89.98%). In terms of the variety, the lowest fruit infestation at harvest was observed for Hong houy (56.02%) as compared to Bhur Litchi 1 (73.28%) and Bhur Litchi 2 (73.45%). There were no significant differences in fruit drop percent and percent infestation of dropped fruits between the treatments and varieties tested. Heavy fruit drop was observed in the third week, due to unknown reasons, which then decreased over the fruit development stages. Fruit borer infestation seems to increase rapidly after the fifth and eighth weeks indicating that most of the fruit borer damage occurs at the fruit maturity stage after fruit colour break. Therefore, the last application of cypermethrin 10% EC at the fruit colour break stage was found necessary to reduce fruit infestation during this vulnerable pest infestation period besides scheduled application of Azadirachtin and Imidacloprid at the early fruit development period.
Keywords: Litchi fruit and shoot borer; Emerging pest; Pest management