Harvest Weed Seed Control – getting the best results

Take home messages

• Regardless of your choice of tool for harvest weed seed control (HWSC), it will only deal with the weed seeds that enter the front of the harvester.
• The amount of weed seeds that enter the header front depends on the season, the weed phenology and crop growth, and weed competition.
• Chaff lining is an entry point into HWSC.
• Chaff decking is best suited for a controlled traffic farming (CTF) system.
• The choice of seed impact mill will be based around many considerations, including header model and make, and local supply and service of the mill.
• Stripper fronts have the ability to capture as much weed seed in their chaff component as draper fronts.

Background

Harvest weed seed control (HWSC) is a key component of the WeedSmart Big 6 . It is our final chance to non-chemically reduce the amount of problematic weed seeds that are returned to our weed seed bank.

HWSC options include chaff carts, narrow windrow burning, direct baling, and the more recent options of chaff lining, chaff decking and the use of a seed impact mill.

The decision of which HWSC tool to implement on your farm is a difficult one, as no one tool suits all farms. Weed type, crops grown, rainfall, yield potential, local machinery dealers – all of these things and more, influence the decision of what HWSC tool to utilise.

Options

Chaff carts rely on weed seeds being collected through the harvester before being transported off the back of the sieves via a conveyor belt to the cart. Chaff dumps are then either lined up for ease of burning before the next seeding or grazed if in a mixed farming system. Some growers have also experimented with baling the chaff and have reported great success.

Originally known as ‘windrow rotting’, chaff lining has been championed by Western Australian (WA) growers, including Mic Fels. The concept involves funnelling the chaff fraction of crop residue (containing weed seeds) into a confined row directly behind the harvester using a narrow chute. The chaff and weed seeds are then left to rot down over time. To promote rotting, the chaff lines need to be placed in the same location year after year.

Chaff decking is a form of chaff lining, which combines dual chute placement of the chaff onto the wheel marks with the hostile environment that compaction and the constant traffic of a controlled traffic farming (CTF) system creates on the line.

Seed impact mills have been around for a couple of decades now, initiated by the work of Ray Harrington in the late 1990s. It is only in the last five years, that they have been available as integrated units. Seed impact mills work by crushing, grinding and impacting the weed seeds contained in the chaff fraction of the harvest residue.

Discussion

Analysis of chaff carts as a HWSC tool

Strengths

• Capture of problematic weed seeds that can be dealt with.
• Dual purpose chaff – salinity management, livestock grazing.
• Can be baled.

Weaknesses

• Percentage of weed seeds entering the header – weed type, difference within a species, harvest timing (same for all HWSC strategies!).
• Relies on burning to completely remove/reduce weed seeds.
• Grazing chaff heaps can result in weed seed spread through the paddock, via chaff spread or animal faeces.
• Extra fuel consumption.
• More time consuming.
• Nutrient loss.

Analysis of chaff lining as a HWSC tool

Strengths

• Capture of problematic weed seeds that can be dealt with.
• Cheaper than other HWSC options – can make your own or buy a retro fit model.
• Concentration of weed seeds into a localised, known area.
• Non-chemical.
• No burning involved.

Weaknesses

• Percentage of weed seeds entering the header – weed type, difference within a species, harvest timing (same for all HWSC strategies!).
• Ideally, the header is required to follow the same marks each year.
• Lack of decomposition.
• Volunteer grain germinating in the line (e.g., wheat in barley).
• Nutrient concentration.
• Potential nutrient loss.
• Crop establishment through the chaff line in subsequent years.

Analysis of chaff decks as a HWSC tool

Strengths

• Same as those listed for chaff lining.
• More hostile environment for weeds on the tram lines/tracks – soil compaction, competition, physical damage from wheels.
• Better summer weed control through reduced dust which impedes herbicide uptake.

Weaknesses

• Same as those listed for chaff lining.
• Reliant on having CTF set up.

Analysis of seed impact mills as a HWSC tool

Strengths

• Percentage kill/control rate.
• No burning.
• Organic matter back into the ground.
• Fast-paced development of impact mill technology.

Weaknesses

• Capital outlay.
• Fuel consumption/efficiency.
• One make and model doesn’t currently suit all situations.
• Crop moisture/greenness.
• Blockages.
• Wear and tear (maintenance).
• Snails, rocks/dirt.

The choice of seed impact mill will be determined by the header type and make, local dealer, back-up service available and what the best fit is in the farming enterprise.

Summary of the Yorke Peninsula seed impact mill experience

• Don’t rush the harvest, particularly after frosts and/or a wet spring that has resulted in re-growth.
• Ensure crop is as dry as possible to prevent blockages.
• Mills do not efficiently process lentils that have stems that remain green at harvest.
• Seed impact mills are increasing in their longevity.
• Great results can be achieved with a stripper front and a seed impact mill.
• ‘Drive to the mill’ – I like this phrase!

Further considerations regarding HWSC options

• Cash flow – what you can afford and the return on investment (ROI)?
• Continuous cropping versus mixed farming – can chaff be used elsewhere on the farm?
• Phenology of the problematic weed/s – dormancy, maturity, growth habit, etc.
• Burning permits in your local council – tighter restrictions regarding burning.
• Rainfall and yield potential – how much chaff will you be dealing with?
• Ongoing expenses – repairs and maintenance.
• What is my soil nutritional health like? For example, what are the nutritional costs to me to replace the nutrients lost? Potassium (K) makes up a big part of the nutritional cost in places like WA.
• Can I adopt other components of the WeedSmart Big 6, other than HWSC?

Conclusion

• All HWSC strategies only deal with the weed seeds that enter the harvester front.
• Not all strategies will suit everyone.
• Labour will also play an integral part of your decision making.
• Peter Newman’s HWSC calculator is a great starting point to compare the cost of the different strategies.
• Chaff lining/decking is an economic/low-cost entry into HWSC. It relies heavily on the decay of weed seeds within the line as a means of weed control and reduction of weed seed into the soil bank. However, during the past few seasons, particularly in South Australia (SA), dry summers with minimal rain have occurred, which has led to little or no decomposition of the weed seeds in the chaff line. Evidence of this has been measured in trials by Gurjeet Gill (SA) and John Broster and Annie Ruttledge (NSW) through their trial work on weed seed decay in chaff lines.

Acknowledgements

The author would like to thank the following people for their work that has contributed to this report: Gurjeet Gill, University of Adelaide; Michael Walsh, University of Sydney; Greg Condon and Peter Newman, WeedSmart; John Broster, Charles Sturt University and Annie Ruttledge, Department of Agriculture & Fisheries. WeedSmart is financially supported by its numerous partners with the GRDC being the principal investor.

Useful resources

AHRI, 2019, What’s the cost of harvest weed seed control for YOU?

Contact details

Chris Davey
YP AG, WeedSmart
1-3 Kennett Street North, Kadina
0428466675
chris@ypag.com.au
@CropDoctor54