Herbicide resistance has been a hot topic for a while now but is it really an issue for every grower? Well, unfortunately, the short answer is yes, weed resistance is a major risk to Australian farming. Continual use of the same chemicals year on year is contributing to a growing resistance issue around the nation.
The bad news is that once a weed becomes resistant to a particular group, the options for controlling that weed are then limited. One by one we lose chemicals that can effectively kill a weed and there is very little new chemistry on the way.
The good news is that growers are in a position to slow the rate of resistance, meaning that a broader range of chemicals can continue to be used and reduce the long term cost of controlling weeds on farm.
Growers have a great opportunity to plan their chemical rotations now, for the long term benefit of their farm production.
What we’re seeing today
Recently, we analysed some resistant test results from across Australia to get a broader view of what is happening with the efficacy of some of Australia’s most needed chemicals to control ryegrass.
The results showed that we have to be planning now to rotate our chemical groups more wisely so we can use them longer term. If farmers and advisors don’t change their current practices now we will end up with little options to control certain weeds like Ryegrass and Radish, etc.
Elders Rygrass resistance test results, 2011
The above paints a pretty scary picture with more than 50% resistance in both group A chemicals like Clethodim/Tralkoxyodim and group B Triasulfuron/Chlorsulfuron chemicals already. Trifluralin resistance is growing and one sample out of 20 coming back resistant to Glyphosate.
The good news is while we can’t stop the onset of resistance we certainly can delay it by using the chemicals available more wisely.
What can you do about it?
As now is the time to plan for which knockdown and pre-emergent chemicals will be used this season, we suggest you consider the following.
To delay the onset of Glyphosate resistance use an alternative chemical group in your knockdown spray like Paraquat which is group L (rather than group M) and has a different mode of action. Ideally, you would use a Paraquat spray at least once in the paddock rotation or at least once every 4 years if you crop on crop.
The same principal should be followed with your pre-emergent and post emergent sprays.
Ultimately a whole integrated weed management plan should be used on your farm today.
Considerations for your integrated weed management plan
- Rotate herbicides with different modes of action (MOA). When you are onto a good thing — don’t stick to it.
- Develop a diverse crop rotation to allow different herbicide MOA and cultural weed control methods.
- Do not cut herbicide rates — always use full label rates.
- This is a numbers game – a resistance management plan must keep seed numbers as close to zero as possible. Aim for 100% weed control with every operation.
- Use a double knock where possible.
- Delay seeding date to maximise weed emergence and subsequent kill.
- Increase crop competition.
- Use multiple weed control methods, such as spray topping, crop topping, chaff carts, hay/silage and narrow windrow burning, that minimise the likelihood of escaped weeds setting seed.
- Employ vigilant seed cleaning methods.
- Ensure machinery is cleaned properly.
- Develop a flexible and diverse strategy tailored to your individual farming enterprise.
For more information contact one of our agronomists