Dore & Co.

Recording spot spraying points to develop variable rate herbicide spray.

Who: Dore & Co.
Location: Euramo and Bilyana, south of Tully
Property size: 590 ha

The Dore brothers crop is predominantly sugarcane. Guinea grass is a major weed on the Dore farm, and a significant issue in the wider industry as it reduces productivity and increases herbicide costs.

“Guinea grass is a major issue within the industry. If this trial strategy works it has the potential to reduce the amount of pre-emergent herbicide being used in the immediate crop and in the future ratoons.”

The project

Recording spot spraying points to develop variable rate herbicide spray

Trial block details:
Crop: sugarcane
Trial block size: 4.19 ha
Soil type: Bulgun soil series

If successful, the practice change has the potential to be used across 100 % of the Dore’s farm.

An economic analysis of the trial provided the following key findings:

  • Results indicate that the variable spray would achieve a cost saving of $4.29 per hectare.
  • Capital costs would be repaid in six years, and would result in an annualised equivalent benefit of $1.85 per hectare.
  • The results were sensitive to the ratio of high weed pressure zones to low weed pressure zones, and the variable spray system would only be worthwhile if the low spray rate is applied to at least 67.5 % of ratoons on average.

The Dore’s herbicide rates were informed by their impression of the weed status, whether it was “clean”, or “dirty”.

Standard practice for dirty blocks, or those with a reasonable quantity of guinea grass infestation has been to use a high rate of pre-emergent herbicide across the entire block, which meant that more herbicide than necessary was being applied to the majority of the field.

Clean blocks had a lower rate used, which meant small areas with guinea grass had the potential to expand and in later ratoons the block would gain “dirty” status.

Trial status and results

The Dore brothers trialled a variable rate of herbicide application based on weed pressure maps that were created using a modified spot sprayer. The aim was to reduce the amount of pre-emergent herbicide usage, without compromising weed control.

On the 4.2 hectare trial block, a modified spot sprayer was used to record a GPS location point (with a 20 metre radius buffering zone) from which was developed a variable rate prescription for herbicide application.

Having the ability to map weed distribution will assist with farm planning, and herbicide usage which is a strategy that not only assists with maintaining productivity and increasing profitability, but has potential water quality benefits.

Weed distribution can also influence farm planning and crop rotation. Blocks with major infestations may be fallowed earlier than planned so that weed control measures can be used in the fallow, such as using knockdown herbicides rather than pre-emergent.

Initial spray maps will be compared with further spray maps to evaluate the benefits of the technology. The Dores expect that infestation areas will, at least, be stable and that the amount of pre-emergent herbicide used on the farm will reduce.

2015: 3.75 ha (Red) 0.95 ha (Blue)
2016: 3.45 ha (Red) 1.25 ha (Blue)

The blue area represents the spot sprayer points buffered by a 20 m radius. This is where ideally the higher rate of pre-emergent herbicides would be used as this is the high pressure area. This paddock had the standard low rate across the entire paddock.

The 2016 Spot Spray Map shows an increase in the buffered area of the spot spray points. Due to some issues with the prescriptions, and then with the sprayer, no variable rate applications were made.

Block 8 was spot sprayed in 2015 (LEFT) and 2016 (RIGHT), both show centre tram with lots of blue.

2015: (Red 2.38 Ha, Blue 1.29 Ha)

2016: (Red 2.00 Ha, Blue 1.68 Ha)

Images like this has lead the Dores to consider fallowing this block earlier than anticipated so products like glyphosate and verdict in the fallows can be used to control the Guinea grass problem, rather than relying on pre-emergent herbicides and spot spraying alone.

* Holligan, E. (2016), Variable rate herbicide spray – Dore & Co.: Economic analysis. Department of Agriculture and Fisheries (DAF), Queensland.