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Australian Herbicide Resistance Initiative (AHRI)

To win the war you must win the battles

Machines plowing field

As Darkan farmer and inventor of the Harrington Seed Destructor, Ray Harrington, aptly says, “Harvest weed seed control is a pain in the ….” – but it is an imperative tool in continuous cropping systems”.

“To win the war you must win the battles. Harvest weed seed control is an important battle. If you’re not implementing weed seed control at harvest, you’re out of the farming game”.

It’s a tough message to hear, and it’s one that growers from Wagin, Lake Grace and Ravensthorpe in Western Australia heard at AHRI’s “More crop, less weeds – sustainably!” workshops last week.

The only rule Ray Harrington has in farming is that there are no rules. He says that you have to be willing to do whatever it takes to stop weed seeds entering the seed bank.

Many growers and advisers are asking the question, “Should I windrow burn, buy a chaff cart, or wait for the Harrington Seed Destructor”? We now feel that we have a lot of information that can help with this decision.

Know all about how these systems work but want to explore the cost? Click here to skip to the financials section. If not, or you’d like a refresher, keep reading!

Harvest weed seed control tools – where do they fit?

  1. Narrow windrow burning – best suited to low to medium rainfall zones to facilitate burning of the windrow without burning the whole paddock and to minimise nutrient removal in residue.
  2. Chaff cart – everywhere.  Cost effective, practical tool that suits all rainfall zones, but does still involve burning of some crop residue in most situations.
  3. Bale Direct – where a reliable market for straw exists close by.
  4. Harrington Seed Destructor (HSD) – Larger areas of crop in medium to high rainfall zones.

Summary of the harvest weed seed control tools

Below, we briefly explore the harvest weed seed control options currently used across Australia to capture and/or destroy weed seeds at harvest.

Chaff carts

This HWSC system consists of a chaff collection and transfer mechanism attached to a grain harvester, capturing the chaff fraction in a tow-behind cart (Figure 1). The chaff cart has been shown to achieve the collection and removal of high proportions of seed from crop-infesting populations of annual ryegrass, wild radish and wild oat.

Typically, the collected chaff is then dumped in chaff heaps in lines across fields in preparation for subsequent burning to achieve weed seed destruction. Alternatively, chaff material is a valuable livestock feed source and can be grazed in-situ or, in some instances, collected for use in feedlots.

Western Australian grain grower Lance Turner pioneered the elevator delivery system in the chaff cart (from the original blower transfer system) (Figure 1). This approach significantly improved chaff delivery into the cart, making the chaff cart much easier to use. The elevator system is now available on commercially sold chaff carts.

Chaff cart system

Figure 1. Chaff cart system in operation during commercial wheat crop harvest (left) with the Lance Turner pioneered elevator delivery system, shown here in the latest commercially available model from Tecfarm (right).

Narrow windrow burning

The simple but effective narrow windrow burning system is currently the most widely adopted HWSC system in Australia. This system uses a grain harvester mounted chute to concentrate all of the exiting chaff and straw residues into a narrow windrow about 500 to 600mm wide (Figure 2).

These narrow windrows are subsequently burnt under the right environmental conditions to avoid burning the entire paddock (Figure 2). The concentration of chaff and straw residues increases the duration and temperature of burning, as the higher the temperature, the more weed seeds destroyed. Narrow windrow burning has been shown to kill 99% of weed seeds for both annual ryegrass and wild radish in wheat, canola, and lupin chaff and straw residues.

Western Australian grain growers Andrew and Rod Messina have perfected this HWSC technique and burn around 10,000 ha of narrow windrows every autumn, giving them the advantage of dry sowing their crops.

Windrows by chaff chute

Figure 2. Narrow windrows formed by a chaff chute mounted on the rear of
the harvester (left) are then later burnt in autumn (right).

Bale direct

The Bale Direct System developed by the Shields family at Wongan Hills consists of a large square baler directly attached to the harvester that constructs bales from the chaff and straw residues as during harvest (Figure 3).

This system serves to both capture weed seeds and bale harvest residues for livestock feed. AHRI studies determined that 95% of annual ryegrass seeds are collected and removed from fields using this system. However, the availability of suitable markets for the baled material has limited the adoption of this system by Australian growers.

Bale system collecting and baling chaff

Figure 3. Bale direct system collecting and baling chaff and straw residues.

Harrington Seed Destructor (HSD)

The Harrington Seed Destructor (HSD) is a unique weed seed control system developed by Ray Harrington that processes the weed seed bearing chaff fraction during harvest to destroy any weeds before returning this material to the paddock (Figure 4). Unlike other harvest weed seed control systems, there is no need for any post-harvest operations and all harvest residues are retained.

AHRI research has shown that the HSD consistently destroys 95% of annual ryegrass, wild radish, wild oats and brome grass seed present in the chaff fraction.

Encouraging field results led to GRDC awarding the commercial manufacturing license to de Bruin Engineering of Mount Gambier, South Australia in 2012.

Schematic view of a cage mill

Figure 4. Schematic view of a cage mill showing chaff entry (left) in the commercially available Harrington Seed Destructor from de Bruin Engineering (right).

The role of harvest weed seed control tools in driving weed numbers down

It is important to take a long-term approach to weed control. This is where the real value of HWSC systems become apparent – as part of a system including both early-season weed control practices (herbicides etc.) on weed seedlings and HWSC on late-season mature seed bearing weeds.

The combined impact of herbicides plus HWSC over 10 consecutive seasons (2002 to 2011) on annual ryegrass populations was monitored in 25 large, commercial Western Australian cropping paddocks (Figure 5). Growers nominated ‘‘problem paddocks’’ with high (35 to 50 plants / m2) in-crop annual ryegrass densities for this focus paddock study.

Over 10 consecutive growing seasons, herbicide focused weed management practices were implemented on these paddocks to reduce annual ryegrass populations. Unsurprisingly, effective herbicide treatments reduced in-crop annual ryegrass populations within five consecutive growing seasons (Figure 5). However, it was only in the paddocks where both early-season herbicides and HWSC were routinely practiced that very low weed densities were achieved. Therefore, combining both herbicide and non-herbicide weed control methods is crucial for achieving and maintaining low weed seed bank numbers.

Graph showing Influence of the long-term use of herbicides alone and herbicides

Figure 5. Influence of the long-term use of herbicides alone and herbicides plus harvest weed seed control (HWSC) on in-crop annual ryegrass plant densities in northern WA cropping fields. Capped bars represent the standard error values showing variation around the mean annual ryegrass populations in 17 fields (Herbicides) or 8 fields (Herbicides plus HWSC).

How much do they cost?

A tool such as narrow windrow burning may appear inexpensive on face value, however, when the cost of nutrient removal (mainly N & K) is included the true cost of this practice increases. The HSD appears very expensive on face value, however, given that there is no nutrient removal with this practice, the cost of this machinery is relatively similar to other options if the capital cost is averaged over a large enough harvest area. The cost of the bale direct system can be re-couped, and in some cases profit made when bales are sold.

For more information about costs and to download the factsheets, click on the ‘workshop downloads’ link below.

Table 1. Cost ($/ha) of harvest weed seed control tools for differing areas harvested with one machine. Cost includes finance, labour, fuel, repairs and maintenance and nutrient removal. Assumes a wheat crop yield of 2 t/ha. Nutrient removal cost assumes 50% nutrient efficiency.
Table showing cost of harvest weed seed control tools for differing areas harvested with one machine.

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