Crop weeds: weed management at harvest
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This management strategy provides an opportunity to control weed seed set in the pasture and during harvest. It physically removes viable seed from the paddock by collecting weed seed and grazing crop residues.
Baling crop residue directly from the header.jpg
Seeds of grasses like barley grass are not highly palatable. These grasses need to be grazed before seed heads are produced.jpg
Modifications to the header to generate a narrow chaff trail concentrating weed seeds and allowing a hot burn.jpg
Weed seed removal can be achieved in two ways:
- Harvesting provides an excellent opportunity to remove weed seeds from the system and prevent them from being spread across the paddock or farm. Collecting seed at harvest has the potential to be a useful component of an integrated weed management program.
- Grazing weed contaminated crop residue can be a cost-effective way of controlling weed growth. Animal digestion of weed seeds prevents a large proportion of seeds from entering the seedbank.
Weed seed collection at harvest will not increase grain yield, as the weeds have already caused damage to the crop. The tactic can only prevent increases to the seedbank, although it may give a subsequent yield advantage to the next season’s crop through reduced weed numbers during the season.
Management of weed seed removal at harvest
Factors affecting weed seed removal
The weed species has a major influence on the proportion of weed seed removed from the paddock when collected at harvest. For example, annual ryegrass is much more available to collect than wild oats, which tend to shed seed before harvest. Successful collection and control depends on the weed:
- Maturing at the same time, or later than, the crop being harvested.
- Having seeds at a similar or greater height compared with the crop being harvested — this may be overcome by setting the header at a height so weed seeds are captured.
- Having seeds that do not shed or shatter before or during harvest.
- Having seeds that can be threshed and are of a size that end up in the chaff component of the harvested crop.
- Timing of harvest will affect the amount of seed removed from the paddock when residue is collected. As harvest is delayed, a greater proportion of the weeds presented will shatter or lodge, reducing the total proportion of seed able to be collected.
Disposal of chaff and seed
A strategy to dispose of chaff dumps or large quantities of baled straw must be implemented. These two products will contain the collected seed and therefore need to be managed appropriately. Chaff dumps are usually burned or fed to livestock, and both options require careful management.
Harvest weed seed systems
Redekop Seed Control Unit, an integrated reversible cage mill with blade system that provides Harvest Weed Seed Control, was assessed for volunteer canola control. Blade configuration in combination with chaff feeding rate did not affect volunteer canola control, which remained above 99%.
Harvest Weed Seed Control (HWSC) targets weed seeds at harvest to prevent them from returning to the seedbank. It is an important herbicide resistant management tool in Australia, and is being researched in Western Canada.
There are currently four integrated impact mills on the market that provide HWSC: the iHSD v.12, the Seed Terminator, the WeedHOG and, the Canadian-made Redekop Seed Control Unit (SCU). The SCU is an impact mill that incorporates a blade system in the centre of the mill with the goal to increase suction into the mill and airflow through it.
The objectives of this research by AAFC Lacombe was to evaluate weed seed control with the Redekop SCU, optimize blade configurations between all fan blades and a cutting blade/fan blade combination, and determine if weed seed control levels remain high at higher chaff feeding rates.
Volunteer canola was chosen for its high viability, limited primary dormancy and rapid germination, making it an ideal study species for HWSC. It is also the 4th most abundant weed in annual field crops on the Canadian Prairies based on the most recent weed survey conducted after post-emergence herbicide application. Canola also showed similar destruction rates as other weed species when previously tested by other impact mills.
Wheat chaff was collected from a field near Saskatoon, Saskatchewan with a chaff cart system. Ten thousand seeds of canola was mixed with 3.056 kg of wheat chaff, and fed into the cage mill with a conveyor belt. Chaff feeding rates were 5 or 10 tonnes of chaff per hour.
Blade configurations tested included 8 fan blades, or a combination of 4 fan blades and 4 cutting blades.
After going through the cage mill, processed samples were cleaned, and the recovered whole and partial seeds were placed into germination boxes to test for viability.
Greater than 99% control
Blade configuration, chaff feeding rate, and their interactions did not significantly differ for volunteer canola control. Average volunteer canola control across treatments was 99.5%. This is similar to control previously observed by the tow-behind Harrington Seed Destructor on volunteer canola, as well as being in the range of control measured on other weeds with the iHSD. It is also the same range of control expected of the Seed Terminator system.
The goal behind the addition of the blades is to improve airflow and suction through the mill in an effort to decrease energy requirements. While the energy requirements were not tested in this study, if lower energy needs are achieved by the addition, the incorporation of the blade system is an important step in the evolution of integrated mill systems for weed control as it may result in decreased power requirements, decreased fuel use and decreased operating costs.
Financial support for this research was provided by Redekop Manufacturing.