According to local Paddock to Reef sugar cane water quality monitoring trials, cane farmers can greatly reduce herbicide loss if there is a significant gap of at least three weeks between herbicide application and substantial rainfall. The trials also found that applying herbicide before an infiltrating rainfall helps to incorporate herbicide into the soil and further reduces the risk of loss. Overhead irrigation has the same effect.
How it works
The trials show two complimentary strategies for keeping herbicides in the paddock where you need them.
1. Keep an eye on short term rainfall predictions
The wet season came early in 2010/11. Herbicides were applied and within seven days there was a runoff event. Enough rain fell to saturate the soil and flow off the property. The herbicide was still fresh on the surface of the cane trash blanket; therefore a relatively large amount was lost in this early runoff event.
The wet season data for the season showed that the majority of herbicide loss occurred within twenty days of application. In fact, within one month of herbicide application, approximately 92% of the total wet season runoff loss of the regulated herbicides had occurred although only 6% of the season’s rainfall runoff had occurred.
During this period the trials experienced heavy rains. A total of 3300 mm of rainfall was recorded between 1 September 2010 and 30 April 2011, well above the long-term average of 1468 mm. This resulted in 1751 mm of runoff. The regulated residual herbicides applied were found in high concentrations in the first runoff event and then rapidly declined.
2. Time herbicide application to coincide with infiltrating rain or follow with overhead irrigation
Applying herbicide prior to an infiltrating rainfall event—one that does not runoff —or following herbicide application with overhead irrigation moves herbicide through the trash blanket and into the surface soil, making it less available for runoff. This was demonstrated at the Paddock to Reef trial sites in the 2009/10 wet season when there was very little herbicide detected in the runoff collected with a much longer time between application and a runoff event and a beneficial 8 mms of rainfall seven days after application.
Herbicide application should not be taken lightly. John Agnew, MAPS Senior Productivity Officer and Paddock to Reef Agronomist, recommends that as growers prepare their cane for the new season they carefully follow recommendations on the product label and any associated regulations. These may include waiting at least two days after herbicide application on bare soil before watering in, not applying herbicides to water logged soil or delaying application if runoff-causing rainfall is predicted within 48 hours of the planned application.
About Paddock to Reef
The Paddock to Reef sugar cane water quality monitoring trials aim to show that industry-promoted best practices can improve grower’s profitability and have water quality benefits.
Paddock to Reef uses water quality monitoring and modelling tools across paddock, catchment and marine scales to measure and report on improvements in agricultural runoff entering the Great Barrier Reef catchments. In the Mackay Whitsunday region, Paddock to Reef is coordinated by Reef Catchments and conducted by the Department of Natural Resources and Mines (DNRM), Mackay Area Productivity Services (MAPS) and two local sugarcane farmers.
The water quality monitoring sites are on two local farms with different soil types—loam over clay and black cracking clay—that represent 44% of soils in the Mackay Whitsunday area. Both sites are looking at the effect of row spacing (controlled traffic versus conventional), nutrient (mainly nitrogen and phosphorus) and herbicide management (knockdowns and residuals) on productivity, profitability and water quality.
For more information on the Paddock to Reef trials in Mackay contact Belinda Billing at Reef Catchments on 4968 4208 or firstname.lastname@example.org.