The weakest link in weed control programs in most northern region farming systems is the summer fallow. With no competition from crops, uncontrolled weeds can use the abundant water and nutrients to produce lots of seed, putting additional pressure on future weed control programs.
For the last three decades glyphosate, and its tank mix partners, has provided effective summer weed control and allowed the implementation of conservation farming techniques, but with glyphosate resistance affecting more and more paddocks, summer fallow management needs to change.
Mark Congreve, senior consultant with ICAN, says that growers are implementing new strategies, not simply to replace glyphosate but to extend its use in their farming system.
“There are two main signs that growers need to look for to detect if their weed populations are becoming more resistant to herbicides,” he says. “The first is to take note of ‘survivor’ weeds – individual weeds that appear unaffected after a spray event that has killed the surrounding weed plants. The second sign is ‘rate creep’. This is where a herbicide is still effective but only when higher and higher rates are applied.”
Growers should not ignore either of these signs, which could indicate changes in the herbicide resistance status. Mr Congreve suggests growers should seek agronomic advice and test weeds for their susceptibility to a range of herbicides.
What should I do as a first step, even if there are no definite signs of glyphosate resistance?
Answer: Do something different. Double-knock, whenever possible. Implement the 2 + 2 + 0 strategy. Wherever possible use the double-knock combination of two herbicides or a herbicide followed with a non-herbicide tactic (eg cultivation), particularly while glyphosate resistance levels are still relatively low.
Are there any other knock-down options for grass weed control in the fallow?
Answer: Consider using Shogun, a recently registered knock-down herbicide for use in fallow situations. Shogun (propaquizafop) is a Group A ‘fop’ herbicide.
What options exist for glyphosate resistant broadleaf weeds such as fleabane or sowthistle?
Answer: There are a number of Group G and I herbicides registered for these problem weeds. Check product labels for details and timing.
How to ask a WeedSmart question
- Ask questions about herbicide options in summer fallow on the WeedSmart Innovations Facebook page, Twitter @WeedSmartAU or www.weedsmart.org.au. ‘Weedsmart’ is an initiative to enhance on-farm practices and promote the long term, sustainable use of herbicides in Australian agriculture.
