By Tim Bartimote – Cropping Officer
For the last two seasons (2019, 2020) Local Land Services has been funded through the GRDC (Grains Research and Development Corporation) to undertake in-field demonstrations of Harvest Weed Seed Control (HWSC) around Gilgandra and Parkes.
Project aim
This project aims to demonstrate the importance of integrated weed management to maintain adequate long term weed control and minimise herbicide resistance. These demonstration sites focused on the use of chaff decks as a viable option for ARG weed seed management. This chaff deck method aims to capture weed seeds in the chaff as they pass through the header by separating it from the straw. Chaff is then directed and compiled on the wheel tracks. It is primarily used in operations where a Controlled Traffic Farming (CTF) system is in operation. Chaff decking places weed seeds on wheel tracks, where regular trafficking and higher compaction creates an environment that can inhibit weed germination. Over multiple seasons most weeds can be found on these wheel tracks. This increases the number of potential control options and increases chemical savings e.g., shielded spraying of wheel tracks only.
Demonstrations were located on properties where broadacre continuous cropping is undertaken each season. Each property had identified Annual Rye Grass (ARG) as the major weed threat to production. Primarily due to its ability to compete with crops for resources and develop herbicide resistance.
In 2019, weed burdens were identified on each site, after crop emergence. In 2019, the Parkes site had an average of 26.0 plants/m2 spread evenly across the paddock. Meanwhile, the Gilgandra site had an average of 1.1 plants/m2 but confined to known patches. From 2019 onwards, chaff decks were utilised at these sites during harvest, with the aim to move the ARG population onto the wheel tracks. Local Land Services monitored this transition by identifying ARG hotspots with GPS coordinates and observing how populations differed each season.
The Parkes site incorporated two home-made chaff decks on their headers in the 2019 harvest while the Gilgandra site employed one chaff deck kit and a home-made version in the 2020 season. In 2020, the GPS points in Parkes recorded the emergence of 4, 19, 9 and 68 ARG per m2(Figure 2). The first three points were randomly selected in the space between wheel tracks, while the final GPS point was randomly selected in a wheel track. After one harvest using the chaff deck, the first three points were found to be under the paddock average, while the point in the wheel track recorded a significantly higher ryegrass population than the paddock average of ARG (Figure 1).
Figure 1. Demonstration paddock in April 2020. First emergence of ARG for 2020 with most plants being found in the wheel tracks.
For the Gilgandra site, GPS points, which were on the known patches of ARG in the paddock, found 4, 13, 16 and 12 plants respectively (Figure 3). No ARG could be found on the wheel tracks so these sites started with zero plants. As the chaff decks were fitted for the 2020 harvest, we will begin to understand their impact when monitoring counts begin in 2021.
Figure 2. ARG numbers from the Parkes demonstration site in 2020, after the first use of the chaff decks in 2019. GPS points (blue) 1 to 3 were randomly selected across the paddock. GPS point 4 is on a wheel track. Dotted line (orange) indicates the average number (26 p/m2) of ARG across the demonstration site.
Figure 3. ARG numbers from the Gilgandra demonstration site in 2020, prior to first use of the chaff decks. GPS points (blue) 1 to 4 are found within known ARG patches. GPS point 5 and 6 are on wheel tracks. Dotted line (orange) indicates the average number (1.1 p/m2) of ARG across the demonstration site.
Preliminary Findings
- The ARG population on the wheel tracks increased by nearly 3 times the paddock average at the Parkes site after one season (Figure 2)
- ARG population in GPS points in other parts of the paddock were reduced by more than half at Parkes (Figure 2)
- At Gilgandra, the ARG population, prior to the first use of the chaff decks, was much higher than the paddock average, except on the wheel tracks (Figure 3)
- 2021 ARG counts will determine if the trend continues at the Gilgandra demonstration site
- Home-made chaff decks did well despite the large amount of plant bulk which was due to a good season. Blockages did occur but were minimal
- Mounted cameras near the chaff decks were very helpful in identifying blockages and reducing down-time
- Home-made designs cost close to $1,000 to implement
