Wimmera and Mallee

  • Pre-emergent herbicide efficacy isn’t just about when you are  aBCG logo with white backgroundctually in the sprayrig, its starts at harvest time
  • When double knocking try spraying glyphosate in one direction and then gramoxone in the opposite direction.
  • In the Wimmera maintain water rates of 70-80L/ha and the Mallee at least 50-60L/ha (ensure quality water is used).

Increasingly, growers are also looking towards new technology to ensure the best spraying results. Many growers are finding benefits from using a self-propelled sprayer such as increased efficiency, ability to cover more ground and accurate herbicide application (largely due to the nozzle system). New technologies such as the AIM command system on a CASE IH Patriot controls flow rates as speeds adjusts due to turning etc., have also created interest.

More attention paid to nozzle spacing may also enhance spray performance. Matching nozzle spacing with row spacing gives the opportunity to spray right in between the existing stubble rows. Some Wimmera growers will have 15 inch spacings on both their seeder and sprayer to assist in spraying in high stubble loads. However nozzle spacings should not exceed 25cm to ensure there are no misses.

Further north, in the Victorian Mallee, growers have experienced periods of reduced stubble residues which create different issues to growers in their quest for weed control in some instances continuous cropping systems.

Water rates in different regions:

In the Wimmera environment water rates of 70L-80L/ha are advised when spraying pre-emergent sprays. Summer spray water rates are typically 70L/ha), in the Mallee water rates are used are commonly around 50-60L/ha, while irrigators in the Loddon Mallee growers are using 100L/ha of water when spraying to ensure that they get good coverage.

At one of a number of workshops led by spray specialist, Craig Day in recent years, growers were reminded of the importance of stubble management in ensuring successful chemical weed control.

“Pre-emergent herbicide efficacy isn’t just about when you are actually in the spray rig; it can start at harvest when you’re in the header. Making sure that trash is spread evenly across the header width means that you reduce the trash concentration in the header row – which are often hot spots for the herbicide to bind to in the next season.”

Headland management can also improve penetration. According to Craig Day, matching seeder headland to sprayed headlands will ensure that the direction of travel is running with the stubble row.

“In many systems currently applicators are spraying across the stubble rows on their second headland lap with the spray unit,” he said.

Research findings

Crop Topping Brome Grass: 2012 Manual article, War on Brome

·         Select a variety with a short growing season when wanting to crop top brome grass

·         Sowing early gave the greatest competition for Brome grass

Brome grass behaviour and management – 2010 Manual article Sam Kleemann 

·         The ecology of brome grass is changing, making it increasingly difficult to control in             no-till farming systems

·         There are few effective herbicides that are available for control in cereal cropping                  systems.

·         Aim for two years of consecutive control to deplete the seed bank

Ryegrass control: 2011 IWM approach 

·         Cutting a crop for hay resulted in a 92% reduction in ryegrass heads in the following             year’s crop. Ryegrass numbers at Jil Jil started at 234 heads/m2 and were reduced to           20 heads/m2.

Fleabane control – 2011 Manual article Controlling Flaxleaf fleabane

·         Control fleabane before it begins to elongate (>40cm in height)

·         Spray twice to avoid the need for more expensive herbicides

·         Surpass® and Ally® in addition improved the control of fleabane

·         Germination of fleabane in enhanced no-till systems

WeedSeeker®: 2011 Manual – WeedSeeker® technology 

·         Erect plants compared with prostrate weeds require less spray

·         Economically 80 plants/m2 of barley (simulated brome grass) and wheat (simulated            vol wheat) would be needed to cover the WeedSeeker® application technology.

Advisors are encouraging some growers to spray their knockdowns in one direction and to spray in the opposite direction when applying double knock with gramoxone. This can get around some of the issues of shading in stubble.

Craig Day (Spray safe and Save) Demonstrating spraying in stubble at Nhill at BCG Crop Walk - October 2014.

Craig Day (Spray safe and Save) Demonstrating spraying in stubble at Nhill at BCG Crop Walk – October 2014.

 table 1 pre-em sprays

Table 2. Summer fallow knockdowns & mode of action

Table 2. Summer fallow knockdowns & mode of action

Pre-emergent herbicides

Trifluralin (Treflan) High volatility means it needs to be incorporated very soon after application by mechanical means or by rainfall.
Not very mobile so won’t control seeds at depth.
Delay in incorporation will result in rapid loss of herbicide.
Trifluralin will bind very tightly to surface residue and will not wash off with rainfall
If field has heavy crop residue, more herbicide will be needed to give adequate control

Prosulfocarb + Metolachlor (Boxer Gold): Moderate volatility means it should be incorporated soon after application.
Delay in incorporation will result in loss of herbicide.
Requires water for activation and delay in rainfall could results in less weed control
Prosulfocarb will bind very tightly to surface residue and will not wash off with rainfall
Metolachlor will wash off surface residue with rainfall
only needs about 5–10 mm of rain to wash it in and activate it and too much rain can cause crop damage.
Metolachlor can be lost from residue surface if it stays on the residue for a long time (7-14 d) before a rainfall
Heavy residue will decrease the activity of prosulfocarb the most. May need more herbicide under heavy residue to maintain activity.
Heavy rainfall after application can leach metolachlor below the weed seed zone.
Should only be applied if ground cover by stubble is less than 40-50% and preferably where stubble is standing and using a nozzle that produces coarse droplets.
Pyroxasulfone (Sakura)  Moderate volatility means it should be incorporated soon after application.
Delay in incorporation will result in loss of herbicide.
Requires water for activation and delay in rainfall could results in less weed control
Dimethenamid will wash off crop residue but can be lost by volatility if it remains on surface for a long time (7-14 d) before rainfall.
Heavy rainfall can leach Pyroxasulfone below the weed seed zone and into the crop seed zone.
Result: more crop injury and less weed control.
About 10–15 mm to activate it in the soil. Problems can arise if the soil is dry on the surface but there is moist underneath. A small amount of rain might fall that is sufficient to germinate the weeds but not enough to activate the herbicide.

Crop residues intercept herbicides during application. The majority of most herbicides will wash off the residue with as little as 5 mm of rainfall. However there are differences among herbicides depending on the type of crop residue and the herbicide. Some herbicides, such as metolachlor, can volatilize off the crop residue if rainfall does not occur soon after application. This can be particularly troublesome in summer fallows with heavy reliance on contact sprays as stubble does intercept spray.

Impact of stubble on boom height

When spraying boom height should be adjusted so that the double overlap is taking place at the top of the crop, however if stubble is present and higher that the crop double overlap should take place at the top of the stubble.
Impact of stubble retention on water rate and nozzle/droplet size:

For table below high stubble loads are classified as being >5t/ha.
The higher the water rate the better.
Efficacy of soil applied chemicals will be reduced with surface stubble loads greater than 3t/ha.
Improving droplet deposition in standing stubble:
Nozzles at the smaller end of the Coarse spectrum 65o flat fan are best at up to 80cm, 110o nozzles should be 50cm from the target. As long as double overlap occurs.
Narrower nozzle spacing (25cm vs 50cm)
A cross wind (wind direction is a big factor)
Higher water rates (>60L/ha, 80L/ha better!)
Slower travel speeds, any speed in excess of 16 km/h will impact on the nozzle and increase lift behind the chassis.
In erected stubbles the vertical structure of the stubble row interferes with the side movement of the spray fan and can filter out spray droplets. Coarse or very coarse droplets have more potential to bounce of the stubbles and land on the ground or target underneath.

By  Claire Browne
BCG Research Coordinator
E: claire@bcg.org.au

GRDCLogoStacked_TM_CMYK This research is being conducted by BCG as part of the GRDC Maintaining profitable farming systems with retained stubble initiative (project BWD00024 Maintaining profitable farming systems with retained stubble in Victoria and Tasmania).

Disclaimer: Any recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of the Birchip Cropping Group (BCG) or the Grains Research and Development Corporation (GRDC). No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. BCG and GRDC and contributors to these guidelines may identify products by proprietary or trade names to help readers identify particular types of products. We do not endorse or recommend the products of any manufacturer referred to. Other products may perform as well as or better than those specifically referred to. BCG and GRDC will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information in this publication.
Stubble project overview: This guideline has been developed for BCG Farming Systems Group as part of the Maintaining Profitable Farming Systems with Retained Stubble initiative, funded by the Grains Research and Development Corporation (GRDC). The initiative involves farming systems groups in Victoria, South Australia, southern and central New South Wales and Tasmania collaborating with research organisation’s and agribusiness to explore and address issues for growers that impact the profitability of cropping systems with stubble, including pests, diseases, weeds, nutrition and the physical aspects of sowing and establishing crops in heavy residues.

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