1999 Volume 44 Issue 1 Pages 9-18
Field experiments were conducted to evaluate torpedograss (TG) infestation in sugarcane fields with different days of weeding in plant sugarcane during 1994-1996 on Okinawa island. This experiment was done in both a plant and 1st ratoon sugarcane field on the same site. In the plant sugarcane field, no regrowth of TG was observed until final harvest when weeding was done 45 days after planting (DAP); regrowth observed, however, in the plots weeded at 60DAP or later. Decreasing yield of sugarcane was recognized as weeding was delayed; this decreased rate was recorded as 0.9-1.5% per day during 45-90DAP. In the plant sugarcane field, weeding at 45DAP provided a higher number of tillers and greater elongation of sugarcane stem (stalk), which ultimately resulted in significantly higher yield than late weeding. In the ratoon sugarcane period, no regrowth of TG was observed in the plots weeded at 45DAP, and this resulted in significantly higher yield than in late weeded plot. Around 10 times greater TG biomass was recorded from the 60DAP weeded fields in the ratoon sugarcane period than that in the plant sugarcane period. The yield of ratoon sugarcane of 60DAP or later weeded fields was half that of the weed free or 45DAP weeded field. Overall results indicate that torpedograss should be controlled within 45DAP in the plant sugarcane period for lower weed infestation and to obtain a higher yield in both plant and ratoon sugarcane on Okinawa island.
