Implementing harvest weed seed control in low rainfall zones
Harvest weed seed control (HWSC) relies on having the weed seed enter the front of the header, but this is more difficult to achieve in low biomass crops.
Having said that, growers in low rainfall areas have successfully implemented harvest weed seed control, even in cereal crops yielding 0.5 to 1.5 t/ha.
In 2018, GRDC invested in the collection of ten case studies with growers from the Kwinana East port zone around Merredin, WA to discover what modifications and tactics they were using to successfully collect and destroy weed seeds at harvest in this low to mid rainfall zone. The HWSC methods these growers use are narrow windrow burning, chaff lining, chaff decks, chaff carts and impact mills.
Former Planfarm agronomist, Dani Whyte, visited the growers who are all running very efficient, low cost operations to generate profits in this environment and seeing the benefits of HWSC in their farming systems.
Dani Whye, former Planfarm agronomist, visited ten growers from the Kwinana East port zone around Merridin, WA to discover what modifications and tactics they were using to successfully collect and destroy weed seeds at harvest in this low to mid rainfall zone.
“It is difficult to grow highly competitive crops in this region where the average rainfall range is 200 to 350 mm and the scale of operation often does not allow for high seeding rates and narrow row spacing,” she said. “This means that weeds such as ryegrass tend to have a prostrate growth habit and are generally not ‘held up’ by the crop at harvest. This results in a greater proportion of the weed seed being found closer to the ground where they can escape under the cutter bar, compared to what is typically seen in higher biomass crops.”
Since having the weed seeds enter the header is the critical first step to successful harvest weed seed control the growers have focussed on reducing harvest height to 10 cm or less above ground level. Because the crop biomass is low this does not impact on harvest costs but it is all the more important to ensure the paddocks are free of rocks and other obstacles.
“Along with low harvest height, many of these growers have also made minor modifications to the comb to maximise both grain and weed seed capture,” says Dani. “Sharp knives and lift kits have been shown to help gather the crop and weed seed heads onto the cutter bar in low biomass crops.”
Glen Riethmuller from DPIRD, has recommended attaching coreflute to the finger tyne reel to enhance the harvesting of low yielding crops, and this may also benefit weed seed capture. The coreflute sits approximately 25 mm longer than the reel fingers and has a sweeping action to pull grain and weed heads into the header front and prevent them falling backwards off the knife.
Farming a total area of around 7500 ha at Southern Cross, WA, brothers Clint and Wayne Della Bosca and their wives Jess and Dianne chose to add a chaff deck to their harvester for the 2016 harvest as part of their move into controlled traffic farming. Knowing where the weeds are has given them confidence to sow earlier and to use different herbicide options. It adds flexibility to the system. Having noticed that some weed seed heads were not entering the header front, even though he was harvesting as low as possible, Clint has fitted corflute to the reel and a narrow knife guard and extendable fingers to the header front to capture more weed seed and grain at harvest.
Quick tips for harvest weed seed control in low biomass crops
The most common tactics these ten grain growers used to maximise weed seed capture in low yielding or low biomass crops were to increase crop competition, make some simple modifications to the header front, cut the crop low, harvest weedy paddocks first and use their chosen form of HWSC in every paddock, every year.
WeedSmart western region agronomist, Peter Newman says growers are using these tactics and seeing benefits in their weed control, but there is limited research done to validate many of these practices.
“We do have strong evidence for some things though such as the impact of increasing crop competition any way you can, and cutting crops low to maximise weed seed capture,” he says. “The header front modifications are observed to work well and are generally relatively cheap for growers to trial on their machines and evaluate the benefits themselves.”
1. Crop competition
Establish competitive crops by sowing early, increasing seeding rates and east-west sowing where possible.
Choose competitive varieties, particularly for weedy paddocks.
Reduce row spacing to ‘hold weeds up’ in the crop canopy – a move from 12” to 10” row spacing or adopting paired row sowing can increase yield, reduce weed seed set and aid harvest of both the crop and the weed seed.
2. Header front modifications
Extended fingers and a narrow knife guard/ lift kit fitted to header front.
Narrow knife guard with plastic extension fingers to capture and hold heads on the front so they don’t fall forwards.
Coreflute attached to the finger tyne reel to pull grain and weed heads into the header front and prevent them falling backwards off the knife.
3. Harvest time
Choose a HWSC tactic that suits your farm. They all work well to reduce weed burden but there are differences in cost, additional work, nutrient concentration and stubble management.
Number 1 tactic – harvest 10 to 15 cm off the ground. Paddocks must be clear of stumps and rocks.
Harvest weedy paddocks first before weeds shed their seed or lodge. Clean down the harvester before shifting paddocks.
Chaff decks (pictured), chaff carts, impact mills, chaff lining and narrow windrow burning are all being successfully implemented in the Kwinana East zone.
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