Section 9: Case studies
Jamie’s integrated weed management program started about 12 years ago when sowthistle in fallows was a major problem and a single application of glyphosate/2,4-D mix was giving poor results. Split applications and mixtures were introduced (e.g. glyphosate followed by a 2,4-D application 24 hours later). Since then he has managed more difficult weeds including fleabane and feathertop Rhodes grass.
Jamie has two aims with his agronomic strategy: firstly, to save moisture in fallow and, secondly, to reduce the weed seedbank. Timely spray application and doing "whatever is needed to stop all weed survivors" are key strategies.
Jamie suggests that “most things are difficult, but nothing is impossible. You have to look at the problems you’ve got and work out ways to get around them. Seek advice, because there is plenty around, and don’t try to reinvent the wheel. A ‘take no prisoners’ approach is working for us and is helping to drive down our weed seedbank and keep us in the driving seat.”
Prior to finding patches of Group A resistant wild oats in 1996, winter cropping on ‘Merwood’ consisted of alternating a pulse crop with durum wheat and had been considered by Jeff and many other farmers to be a “good cropping system”. The discovery of Group A resistance greatly concerned Jeff about the future of farming.
While Jeff still has Group A resistant wild oats, the numbers are kept extremely low with the use of rotation, a range of tactics and the growing of competitive crops. Jeff is certain he now has Group B resistant populations of paradoxa grass.
No glyphosate resistance has been detected to date; however, Jeff is always trialing new options and solutions to keep at least one step ahead of the weeds.
Jeff is constantly observing what is happening in the paddocks. If he sees something and doesn’t understand it he finds out the cause.“You need to know what is going on, get some good advice, then do something about it before it is a real problem,” said Jeff.
“Timing is everything with weed management, and seedbank reduction is the secret to weed management. All weed control decisions are so much easier when weed numbers are very low, both in the crop and the following fallow.”
Warwick's main aim has been to remain profitable under a run of tough seasons during the past decade. This necessitates flexible weed management and persistence to meet the changing circumstances. Monitoring weed numbers and levels of control is essential to the program. One year’s weed blow-out can force a change in the cropping program to less profitable options for several years.
Using a diverse range of integrated weed management tactics and planning multiple tactics each season offers flexibility. If one tactic performs poorly, or is too difficult to implement due to seasonal conditions, there is quite often an alternative option available. Warwick now sends samples of suspect weed populations to be tested in the lab if there is no valid reason why the herbicide has failed, so that he knows what he is dealing with.
"Begin an integrated weed management program now – don’t wait until there is a resistance problem. It works better if implemented prior to developing resistance. Be prepared to have a flexible, open-minded approach towards weed management. Continuing to do the same thing, whatever the approach is, can potentially lead to problems. Many tactics on offer are cost-effective and can fit in with your program."
“Don’t be afraid to admit to a glyphosate or any other herbicide resistance problem. The sooner you admit it and take an integrated approach to controlling the weeds, the sooner you’ll get on top of it,” says Warwick.
An integrated weed management program was commenced by the Grays when Group A and B herbicides were failing to control annual ryegrass. It became increasingly apparent that using herbicides alone was not sustainable. They set out with the objective of prolonging the cropping phase and making the cropping more profitable.
Stewart believes they continue to “meet these objectives and improve our situation each year, but it has required a change of attitude. We now realise that we need to use multiple methods of controlling our weeds, especially annual ryegrass. A truly multi-faceted approach is required”.
The Grays’ focus continues on the avoidance of herbicide resistance to other MOAs and in other weed populations. Their integrated weed management program has been working, with their herbicide resistance problem stabilised for the past six years.
The Grays still enjoy the challenges and can see that they have made enough progress to feel they are being successful in managing a serious annual ryegrass problem.
As to advice for others with the same challenges, Stewart still suggests, “You get good advice and be prepared to take a longer-term view, because if you do it right you will get a worthwhile result”.
Annual ryegrass has been resistant to most of the Group A ‘fop’ herbicides since the early 2000s and wild radish resistance to Group B herbicides is widespread. Unfortunately annual ryegrass is now surviving 500 mL/ha of clethodim (Group A ‘dim’), which is a real concern for growers of canola and pulse crops.
Prior to integrated weed management, full-cut cultivation during seedbed preparation dominated the weed management program. Heavy grazing was also used in spring, primarily to control weed seedset. Since the move to 100 per cent cropping, weed management activities have been diversified. However, every crop still needs to make a profit.
Charlie uses an agronomist for herbicide advice and he sources information from agricultural extension events. He also belongs to the ‘Living Farm’ Grower Group which runs 10 grower-directed trials per season, farm walks and a performance benchmarking day in March every year. Involvement with this group provides Charlie with the opportunity to see what's working for other growers and discuss the sustainability of these tactics for his farming system.
The best advice is to prioritise weed problems. Importantly, don’t remain solely focused on the number one problem, as the weed spectrum changes. Be prepared to use as wide a range of tactics as possible, while realising that you won’t use the same tactics every season.
As Charlie says, “Every crop must make a profit, while managing weed numbers and herbicide resistance.”
The effectiveness of on-farm methods of weed seed collection at harvest time: Case studies of growers in the Albany Port Zone