Australia
December 21, 2011
Extreme wet weather during harvest across large areas of the Australian winter cropping zone is posing huge weed management issues for grain growers. Wet conditions have promoted growth of weeds in the standing crop that may have been present prior to the rain, with many summer weeds germinating as soil temperatures increase.
Growers will want to harvest the crops as quickly as possible to maintain grain quality; however this close to harvest issues with herbicide residues are a high risk and it is critical that only registered herbicides or those with a 'permit' are used prior to harvest and that harvest withholding periods are strictly observed. These problems are greatly compounded if weeds resistant to glyphosate or paraquat are present.
Specialist weed management consultant and executive officer of the Australian Glyphosate Sustainability Working Group, Andrew Storrie, says longer term weed management also needs to be considered in these trying times, as a blow-out in weed seed production now will mean three or more years of hard work to get weed numbers back down to manageable levels, depending on the weed species present.
Andrew Storrie with two of the major problem weeds this harvest – fleabane and sowthistle
"This is a second consecutive wet harvest for many growers and it poses a challenge to maintain grain quality and manage longer term weed problems," said Mr Storrie. "Farmers will want to harvest the best quality grain possible and green weeds coming into the front of the header will cause additional staining, increase admixture levels and keep the moisture in grain samples too high to deliver."
"Using a pre-harvest salvage herbicide will be tempting for many growers; however they must first check what products can be used on that particular crop and how long they will have to wait before harvest. Using the wrong product could lead to a residue that exceeds the maximum residue limit (MRL) for that herbicide and crop, or lead to a residue being detected when there is a nil tolerance. Either way, MRL issues can lead to rejection of loads, damage to the reputation of the Australian grains industry and prosecution of those involved."
The GRDC Fact Sheet "Stewardship for late season application of herbicides in winter crops" is a good starting point for detailed information on pre-harvest herbicide use. However growers will need their consultant or adviser to check that registrations or permits are still current. Receival of grain into the system with high residue levels can be disastrous for individuals and the industry.
Growers also need to consider who they are likely to sell grain to, as many end-users have strict limits on what pesticides can be used close to harvest, even if the label has been carefully followed.
Mr Storrie said that, “Growers who are still harvesting might be tempted to forget about the longer term weed management of paddocks in these stressful times, although some additional planning now could save a lot of money controlling weeds in the future.
"Glyphosate resistance is becoming more common across the winter cropping zone and the current late rain means that resistant annual ryegrass and brome grass could set huge amounts of seed which will need to be dealt with over the next few years.
"Seed collection techniques such as chaff carts and narrow windrows for burning will be less effective as many weeds will have lodged and won't be picked up during harvest.
"Growers need to be asking themselves now how will they deal with large seed banks of potentially glyphosate resistant weeds? Will I be able to burn the stubble next autumn? Should I put this weedy paddock to pasture or plant a hay or manure crop in 2012? Is the crop worth harvesting and should the plough come out and be used before these weeds set seed? Are there other options using double knock techniques that can be employed?"
If you suspect glyphosate resistant weeds on your property contact your relevant state expert. Details of who to contact in each state are available from the Australian Glyphosate Working Group web site - www.glyphosateresistance.org.au
The Australian Glyphosate Sustainability Working Group is supported by the Grains Research & Development Corporation (GRDC) and key R&D based crop protection companies with an interest in the sustainability of glyphosate.
The Working Group web site has a range of information about glyphosate resistance including a register of glyphosate resistant weed populations and guides and links for management of glyphosate resistance in different crops and management situations. Go to: www.glyphosateresistance.org.au for more information.
The GRDC’s website also contains information about managing weeds, at www.grdc.com.au/weedlinks
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