An innovative new approach to sugarcane plantation weed management trialled in select Great Barrier Reef catchments have shown a dramatic 90% reduction in runoff of highly soluble herbicides into waterways.
In the lower Burdekin region of northern Australia, scientists from CSIRO, the country’s national science agency, trialled a new technique for applying herbicides to raised beds of furrow irrigated sugar cane by using a specially adapted shielded sprayer.
The technique minimises the likelihood of PSII herbicides such as diuron, atrazine, ametryn and hexazinone coming into contact with irrigation water.
"The conventional application of herbicides in furrow-irrigated sugarcane production is to broadcast spray across the whole field using boom sprayers, which applies herbicides to both beds and furrows.
“Irrigation water then carries the herbicides with the tail water into the drainage channels, into nearby creeks and rivers and potentially into the Great Barrier Reef lagoon", said CSIRO research leader Dr Rai Kookana.
Danni Oliver, also a CSIRO scientist, added: "The geography of the region means that almost the entire flow from the Burdekin River Irrigation Area in the dry season, which runs from July to January, is made up exclusively of irrigation water from sugarcane and other cropping."
According to Jon Brodie of James Cook University, "the amount of some herbicides in creek and estuarine waters during this period regularly exceeds Australian water quality guidelines and could potentially affect, for example, coastal seagrass."
Many of the herbicides used in the region are PSII, which are known to negatively impact reef ecosystems, and are of particular danger to the Great Barrier Reef World Heritage Area and its Reef Marine Park.
Improved farming techniques such as the shielded sprayer help keep herbicides on-farm and have the potential to have a significant and positive impact on water quality around the reef, said Oliver.
Cut by almost half
"The trials show that while there will certainly be some herbicide loss following the first irrigation or rainfall event. The marked decreases in losses documented in this study – a reduction of to 90% - could lead to significant improvements in off-site water quality, particularly during the dry season", she added.
Given the importance of improving Great Barrier Reef water quality, additional testing and demonstration of these technologies across different soil types and farming systems – and possibly with different combinations of chemicals – would provide valuable additional testing of the approach from an industry perspective, say the scientists.
"These trial results are extremely encouraging, and clearly demonstrate that the use of precision herbicide application technologies by the industry, including using shielded sprayers for furrow-irrigated sugarcane cultivation, can be highly effective in reducing herbicide run-off," said Kookana.
The results of the study have been published in the international journal Science of the Total Environment.
Oliver DP, Anderson JS, Davis A, Lewis S, Brodie J, Kookana R. 2013. Banded applications are highly effective in minimising herbicide migration from furrow-irrigated sugar cane . Science of the Total Environment 466-467 (2014) 841-848.