FACTORY-LEVEL STUDY OF INTERNODE BORER INCIDENCE AND JUICE QUALITY LOSSES TOWARDS OPTIMUM BIOCONTROL AND ENHANCED SUGAR RECOVERY

摘要

In South India, the sugarcane internode borer (INB)-Chilo sacchariphagus indicus is a major cause of reduction in juice quality resulting in sugar recovery losses. While research institutions have recommended the release of Trichogramma chilonis as user-friendly, safer and cost-effective biocontrol method to minimise INB infestation, factory-level assessment of local INB severity variations and associated sugar recovery losses, besides local weather-based prediction of INB levels, could help to locally optimize dose rate/timings of Trichogramma releases. The present pilot study at S. V. Sugars, Kancheepuram, Tamil Nadu was made in 2012-13 season to understand the common local variations in INB incidence levels and the associated juice quality/sugar recovery losses, besides the scope to predict local INB severity levels at different crop ages based on weather parameters. The cane basis INB incidence in canes harvested in Dec. 2012, Jan. 2013, and Mar. 2013 was 57.5, 53.0 and 58.5 respectively; while on internode-basis the INB incidence was 5.38, 6.03 and 5.50% respectively. The intemode-based INB percentage (INP) was found to differ significantly between the four age groups of 5-6, 7-8, 9-10 and 11-12 months, averaging 7.0, 5.2, 2.3 and 0.7%, respectively. Further, there was significant interaction between crop age groups and harvest months, indicating that the relative INB levels among the four crop age groups differed with the harvesting month. This result implies that we need to understand the pattern of age-wise INB incidence for individual harvest (planting) months. In addition, the overall maximum INP proportion (48.2%) was in 5-6 months age, followed by 7-8 months age (33,7%), across the total span of vulnerable crop age (5-12 months). Based on this result, we could now more reliably target our future Trichogramma releases mostly to the 5-8 month crop age in our factory area. Further, we found significant positive correlation found between INP levels in the individual phenological stages of the crop (5-6, 7-8, 9-10 and 11-12 months) and the overall maximum temperature in the preceding 3 months. We hope to soon reliably predict the INB levels in different crop ages based on the local weather data (by also including minimum temperature, relative humidity and rainfall). Small Mill Test (SMT) samples drawn in December and March harvests showed that the INB infestation reduced the respective brix values by 0.51 and 0.63 units (from 17.77 and 20.11 in borer-free canes). The respective loss in sugar recovery (CCS %) was 0.86 and 0.38 units (compared to CCS% of 8.29 and 10.01 for borer-free canes). These studies have confirmed that INB causes substantial losses in brix and CCS% in our factory area. We are now planning to improve our sampling strategy in field and SMT to more reliably capture the likely local variations in INB incidence and the associated losses in juice quality (brix) and sugar recovery (CCS%) at factory-level. The present pilot studies have shown that such factory-level R&D can provide several valuable empirical results to form an initial basis to more reliably refine the dose and/or time of Trichogramma releases besides evolve local capacity for short term prediction of INB severity at different crop ages based on local weather parameters. Such R&D model may well be further supported so to empower factory managements to locally refine/optimize such eco-friendly pest control technologies for INB management and so also improve the sugar recovery at factory level. .