Section 7: Managing weeds at harvest
Harvest in action producing narrow chaff rows for burning the following autumn (Photo: A. Storrie)
Weed seed capture and control at harvest can assist other tactics to put the weed seed bank into decline. With correct header set-up, up to 95% of annual ryegrass seeds that enter the harvester can be made to exit in the chaff fraction. If weed seed can be captured, it can be destroyed or removed.
Several systems can effectively reduce the return of annual ryegrass and wild radish seed into the seed-bank, and help put weed populations into decline.
A key strategy for all harvest weed seed control operations is to maximise the percent of weed seeds that enter the header. This means harvesting as early as possible before weed seed is shed, and harvesting as low as is practical e.g. 'beer can height.'
Harvester set-up AHRI Insight 53 (Sept 2015)
During traditional whole paddock stubble burning, the very high temperatures needed for weed seed destruction are not sustained for long enough to kill most weed seeds. By concentrating harvest residues and weed seed into a narrow windrow, fuel load is increased and the period of high temperatures extends to several minutes, improving the kill of weed seeds.
Andrew Messina, (WA grower) explains his experience with designing and using a windrow chute on the back of the header. Home-made, simple design, how to connect and disconnect, tips on optimum design for efficient windrow burning.
Andrew Messina, (WA grower) explains his experience with cutter bar height, chute design, chute height, crop specific tips - canola, how to avoid chute blockages, windrow burning logistics before sowing, efficacy of burn relies on timing.
Michael Walsh, (AHRI) explains the subtleties of burning narrow windrows in canola, pulse and cereal crops. How weather conditions, fire temperature and type of crop stubble all contribute to destruction of the weed seed.
Michael Walsh, (AHRI) shows the results of an effective narrow windrow burning operation.
Peter Newman from AHRI, compares the nutrient losses from chaff heaps and narrow windrows.
Peter Newman from AHRI describes why growers need to vary windrow placement to avoid potassium concentration.
Windrow burning (WeedSmart YouTube clip 2013)
Burning windrows for weed control (DAFWA YouTube clip 2012)
Narrow windrow burn like a pro (WeedSmart YouTube video 2015)
NWB Show and Tell video 1: paddock experiences in SNSW (Grass Roots YouTube video 2015)
NWB Show and Tell video 2: chute designs from the growers' perspective (Grass Roots YouTube video 2015)
7.3 Chaff Carts
Chaff cart in action at Tarin Rock, WA. (Photo: A. Storrie). Chaff carts are towed behind headers during harvest to collect the chaff fraction. Collected piles of chaff are then either burnt the following autumn or used as a source of stock feed.
Lance Turner, (WA grower) experience using chaff carts to manage weed seed at harvest. How chaff carts fit into his integrated weed management plan and the benefits for next seasons sowing program.
Peter Newman from AHRI, explains methods for effectively managing chaff heaps at and after harvest.
Peter Newman from AHRI explains the importance of capturing wild radish seeds at harvest to deplete the weed seed bank.
Rod Messina, (WA grower) experience with burning chaff dumps effectively and comparisons with narrow windrow burning. Benefits for dry sowing the next crop and lowering the weed seed bank.
Ray Harrington, (WA grower and inventor of the Harrington Seed Destructor) windrowing cereals across the rows and success in capturing as much weed seed in the header front to be destroyed by the Harrington Seed Destructor (HSD)
Chaff carts (WeedSmart YouTube clip 2013)
Chaff carts as part of the arsenal (WeedSmart YouTube video 2015)
Grazing Chaff Dumps (WeedSmart YouTube video 2014)
7.4 Bale direct systems
The bale direct system uses a baler attached to the harvester to collect all chaff and straw material. This system requires a large baler to be attached to the back of the harvester. As well as removing weed seeds, the baled material has an economic value as a livestock feed source. (See http://www.glenvar.com/ for the story and development of header-towed bailing systems).
7.5 Harrington Seed Destructor
The HSD is the invention of Ray Harrington, a progressive farmer from Darkan, WA. Developed as a trail behind unit and now also available as an integrated unit that fits into the back of a Class 9 header, the HSD system comprises a chaff processing cage mill, chaff and straw delivery systems. The retention of all harvest residues in the field reduces the loss and/or banding of nutrients and maintains all organic matter to protect the soil from wind and water erosion, as well as reducing evaporation loss when compared with windrow burning, chaff carts and baling.
Weed Seed Destruction - Beer Can Height - Ray Harrington, WA grower and inventor of the Harrington Seed Destructor discusses the importance of lowering the cutter bar on the header to capture as much weed seed as possible for effective harvest weed seed management.
Weed Seed Bank Destruction - Lessons Learned - Windrowing Canola - Ray Harrington, (WA grower and inventor of the Harrington Seed Destructor) experience with weed seed capture when windrowing canola. Different approaches for managing blowouts at harvest and in the following crops
Weed Seed Bank Destruction - Spear grass (Bromus spp.) an Emerging Problem - Ray Harrington, (WA grower and inventor of the Harrington Seed Destructor) success with capturing spear grass (Bromus species) in the header and destroying the seed in the Harrington Seed Destructor (HSD).
Harrington Seed Destructor (WeedSmart YouTube clip 2013)
7.6 Further information
GRDC fact sheets and other publications
Managing the weed seedbank (2010)
GRDC Webinar on beginners guide to harvest management (2014)
This webinar is designed to provide some helpful tips for advisers and growers who wish to explore this option however may be unsure where to start. Topics that will be explored include why to consider harvest weed seed control; what options are available; what paddocks to target; and how to achieve success. Presenters: Mike Walsh (AHRI) & Maurie Street (GOA)
Weed Seed Destruction - Weed Seed Management GRDC YouTube clip
Peter Newman from AHRI explains the importance of harvest weed seed capture and management for getting the weed seed bank into decline.
Weed Seed Destruction - Weed Seed Capture GRDC YouTube clip
Peter Newman from AHRI outlines the different weed seed capture systems and the issues to consider when deciding which best suits a farm business. Issues include: effectiveness of capturing weed seed, nutrient removal and capital cost.
Peter Newman from AHRI explains how herbicides are not the answer to herbicide resistance. Non-herbicide tactics are effective in managing herbicide resistance and running down the weed seed bank.
Ray Harrington, WA grain grower and inventor of the Harrington Seed Destructor, outlines the added benefits weed seed capture at harvest has for sowing the next season.
Broad-acre Weed Control (2010)
Harvest weed seed control: the influence of harvester set up and speed on efficacy in south-eastern Australia wheat crops
John C. Broster, Michael J. Walsh and Allison J. Chambers pp. 38-41, 20th Australasian Weeds Conference (2016)
Influence of annual ryegrass seed retention height on harvest weed seed control (HWSC) and harvest efficiency
Michael J. Walsh, John C. Broster, Charlotte Aves and Stephen B. Powles pp. 42-45, 20th Australasian Weeds Conference (2016
Setting up your header for harvest weed seed control (WeedSmart YouTube video 2015)
Control harvest weed seed set with windrows and crop topping (WeedSmart YouTube video 2015)
Sustaining herbicides with harvest weed seed management (AHRI YouTube clip 2012)
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