RIPENING RESPONSE OF TWELVE SUGARCANE CULTIVARS TO MODDUS® (TRIN-EXAPAC ETHYL)

FIELD experiments were conducted at two sites in the Bundaberg area between 2004 and 2006 to quantify the impact of MODDUS® (trin-exapac ethyl) on increasing CCS in sugarcane. The experiments were undertaken to support product registration and to develop strategies for economic forward extension of the harvesting season. MODDUS® was sprayed from a tractor-based overhead boom at 200 g ai/ha to 12 varieties in replicated trials. In 2004, sequential harvests were conducted at 6, 8 and 10 weeks after a single application of MODDUS®. In 2006, harvests were conducted at 5, 7 and 9 weeks after two applications of MODDUS® two weeks apart. Cane was harvested in 2005 after no further treatment with MODDUS® to assess any residual effects of the 2004 treatment on subsequent yield. Significant responses in CCS, across varieties, of 0.81, 1.00 and 0.99 units were obtained at 6, 8 and 10 weeks after treatment of plant cane in 2004. Increases in sugar yield were significant for the 8 and 10 week harvests. Significant CCS responses were also obtained in the second ratoon crop at this site, but responses were not as large as in plant cane. Q205A and Q225 were less responsive than the other four clones and there was no difference in response by delaying spraying by 14 days. CCS response across another six plant cane clones in 2006 was significantly higher for the earlier spraying (0.96 versus 0.60 units) and average CCS response declined from 1.10 units at 6 weeks after spraying to 0.6 units at 10 weeks. There were also significant varietal effects on CCS response. MODDUS® had no significant effect on cane yield for the duration of the experiments in 2004 and 2006 and the carry-over effect on cane yield was not significant for five of the six varieties in 2005. Significant CCS responses generally resulted in higher sugar yields. CCS response to MODDUS® was controlled by both the level of CCS at spraying and the rate of natural rise in CCS in the five weeks after spraying.