EFFICACY OF PRE-EMERGENT HERBICIDES ON FRESH TRASH BLANKETS - RESULTS ON LATE-HARVESTED RATOONS

摘要

Weed management in ratoons in green-cane trash blanket (GCTB) systems often relies on the use of knockdown herbicides, sometimes together with pre-emergent herbicides such as hexazinone, atrazine and diuron, applied before the out-of-hand stage. Pre-emergent herbicides may have an adverse environmental impact if applied just before or during the wet season. However, application of pre-emergent herbicides on a GCTB just after harvest is not commonly considered as an option by growers due to doubts regarding the chemicals' efficacy with thick trash., Trials were implemented in the 2008-9 season in the Mackay district on grower farms in late-harvest ratoons to evaluate the suitability of this strategy. In each trial, the efficacies of three pre-emergent herbicides were compared when the products were applied on bare soil or on a GCTB. Cane yield was also assessed when pre-emergent herbicides were applied just after harvest compared with the application of knockdowns followed by a pre-emergent herbicide just before the out-of-hand stage. Changes in weed composition were studied in the untreated plots, comparing bare soil and variable amounts of trash. Results show that: more than 6 t/ha of trash on the ground provided significant weed control; each weed species responded differently to different amounts of trash on the ground; there was no difference in efficacy of the pre-emergent herbicides when applied on trash or bare soil; application of pre-emergent herbicides generated significantly higher yield than no treatment, but only if those fields were rapidly infested by weeds.