Effect of Present and Treated Turnera ulmifolia L. on Bagworm and Natural Enemies Population in Oil Palm Plantation

Abstract

Bagworm is the most serious threat to Malaysia's oil palm industry, causing up to 40% crop loss after two years of defoliation. In response to the concomitant decrease in pesticide use, nectariferous plants such as Turnera ulmifolia are increasingly being planted as biological control for bagworm. To fill in the knowledge gap, studies were conducted to determine the effects of field fertiliser application on nectar and flowering of T. ulmifolia and its subsequent effect on parasitoid and bagworm population. Treatments T1 (0.2 g NPK) and T2 (0.2 g NPK + 3.9 g silicon) from semi trial study were further tested on a ten-year-old oil palm plantation in the Samarahan area with a moderate infestation of Metisa plana since early 2017. Data on the number of bagworms and natural enemies were collected weekly during two sampling rounds (February to March and August to September 2020). All data were subjected to Analysis of Variance (ANOVA) using the Statistical Analysis System (SAS) and means for significant treatment effects were separated by LSD tests at a P<0.05 significance level. Improvement in the number of flowers and nectar value was observed seven months after T. ulmifolia was administered with 0.2 g NPK. Consequently, increasing the amount of food is available to parasitoids. As a result, bagworm parasitism, and thus bagworm mortality was higher in the 0.2 g NPK and with silicon plot. The number of live bagworms was greatly reduced in plots with the presence of T. ulmifolia supplied with 0.2 g NPK compared to plots without co-plantation of T. ulmifolia. Fertiliser application positively affected the flowering, and nectar of T. ulmifolia.