Mechanical approach to resistance

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Harvest weed seed tactics have now proven their worth in managing weeds across four Australian states

Ryegrass in a barley crop

Mechanical weed management tactics can remove up to 95 percent of ryegrass seed (pictured) that enters the harvester.

PHOTO: Nicole Baxter

A GRDC-funded trial across 6000 kilometres of southern Australia has demonstrated that harvest weed-seed control tactics can have an impressive impact on ryegrass populations.

In trials spanning Western Australia, South Australia, Victoria and New South Wales, harvest weed seed methods reduced ryegrass emergence by as much as 90 per cent in paddocks with low ryegrass burdens.

Paddocks with high ryegrass burdens (more than 2000 seeds per square metre) were less responsive, with a 30 to 40 per cent reduction in ryegrass emergence. This indicates that harvest weed seed management will take longer to lower ryegrass populations in highly infested paddocks where the residual seedbank is still being exhausted.

Across the 14 trial paddocks scattered between Eyre Peninsula, SA, and Coonamble, NSW, narrow windrow burning and the chaff cart proved as effective as the Harrington Seed Destructor (HSD) at removing ryegrass seed and cost a similar amount per hectare to destroy ryegrass seed (Table 1).

Before harvest, ryegrass plants were counted at each site, along with the number of seeds above harvest height (15 centimetres). In the following autumn, researchers returned to the sites to count the number of emerging ryegrass seedlings – enabling the impact of the HSD, chaff cart and narrow windrow burning on the ryegrass populations to be determined.

Before harvest, ryegrass numbers ranged from 1/m2 to 15/m2, which equated to 28 to 4000 seeds/m2 above cutting height. The average number of ryegrass seeds across the 14 sites was 1270/m2. Ryegrass emergence in the autumn was reduced by about 55 per cent following harvest weed seed treatment.

Fully integrated HSD and harvester on the way

Photo of a seed destructor.

With GRDC funding, University of Adelaide researchers have begun developing a new version of the Harrington Seed Destructor by incorporating the tow-behind milling unit into a class 9 header.


The Harrington Seed Destructor (HSD) is getting a major design overhaul and will be directly incorporated into class 9 and 10 headers – saving growers dollars and time.

The new, integrated approach aims to use less power and have higher capacity than the currently available commercial version, which needs to be towed behind the header. University of Adelaide researchers tested the GRDC-funded integrated HSD initially on a Case header in January 2013.

Instead of the chaff section needing to be flipped out the top of the harvester and pushed into the mill, the new approach processes the chaff at the point where it exits the header, enabling the straw to flow through into the spreader.

Despite using the header’s power system, the new prototype processes chaff at more than 30 tonnes per hour, spreading the crushed mixture consistently across the paddock. The commercial tow-behind HSD will still be available as required for class 6, 7 and 8 headers.

Table 1: Impact of the Harrington Seed Destructor, narrow windrow burning and chaff cart methods on autumn ryegrass density in 14 cropping paddocks across Southern Australia.
 Weed seed management tool
 Reduction in ryegrass emergence (%)
Low ryegrass burden
 High ryegrass burden
 Chaff cart
 75  30
 Windrow burn
 90  29
 Harrington Seed Destructor
 86  38
LSD (p=0.05) 12

More information:

Charlotte Aves,
0409 697 352,


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GRDC Project Code UWA00124

Region National, South, West, North