Published on 29/07/2024
It controls an aggressive, potentially costly competitor before it can affect crop yields; and it provides another mode of action (MOA) to help manage weed resistance to commonly used post-emergence herbicides.
Some populations of wild oats in New Zealand are known to be resistant to Group 1 Fop and Dim/Den herbicides, and at least one was found to be resistant to Group 2 (SU) herbicide in recent surveys by FAR.
Nufarm territory manager Mike Cox says it’s never been more important to build resistance management strategies into cereal spray programmes. And he believes that’s one reason more growers are using Avadex Xtra in autumn sown cereals this year.
Avadex Xtra is a residual thiocarbamate (Group 15) pre-plant incorporated pre-emergence herbicide which has been used for selective wild oat control in NZ for many years.
Mike says even though it’s an ‘old’ product, it now offers an MOA rotation option to the post-emergence herbicide MOAs commonly used for wild oat control in cereals.
“Use of multiple MOA groups in weed control programmes is recognised best practice to minimise development of resistant populations, and prolong the effective life of existing chemistry. Avadex Xtra is already playing a key role in this effort.”
That’s on top of the inherent yield benefits with pre-emergence control of a weed that suppresses cereal yields right from the time that wheat and barley crops germinate.
“Potential yield loss from wild oats can be absolutely phenomenal, up to 75-90%. The beauty of a pre-emergence herbicide like Avadex Xtra is that you’re cutting that risk of yield penalty before it can even take effect, as opposed to relying solely on spraying post-emergence, and effectively waiting until wild oats have already impacted your yields.”
Avadex Xtra will not control germinated or emerged oat seedlings, or oat seeds sitting on the soil surface.
Correctly applied, however, it can significantly reduce wild oat pressure in wheat and barley, with a further benefit being that oat plants which survive treatment may be sensitised to subsequent herbicide application.
Application technique and timing is very important. It should be applied to soil just prior to, or up to three weeks, before drilling wheat or barley.
After application, it must be immediately incorporated to a depth of 5 cm, using light harrows.
When this is done, Avadex Xtra creates a vapour layer below the soil surface.
“As the germinating wild oat seedling grows through this layer, the vapour is taken up by the elongating oat shoot, and it interferes with cell division and elongation.”
Mike says without proper incorporation – which entails two passes over the paddock – results will be disappointing at best.
“If it’s not incorporated, the herbicide just sits on top of the surface of the soil. The vapour created when Avadex Xtra comes into contact with moisture disappears into the atmosphere.”
If applied to very dry soils, Avadex Xtra remains inactive until rain or irrigation is applied. Avadex Xtra should not be applied to soils that are too wet to achieve good incorporation.
Wheat or barley seed needs to be drilled below the depth of incorporation, to prevent potential injury to shallow planted crops, and growers are advised to drill seed at right angles to incorporation.
Wild oats resistant to Group 1 herbicides were found in four of five regions surveyed between 2019 and 2023 by FAR in conjunction with AgResearch, with the highest percentage of resistance recorded in Mid Canterbury.
A single farm surveyed had wild oats resistant to both Group 1 and Group 2 herbicides.
The survey was funded by the Ministry of Business, Innovation and Employment.
For more detail, visit www.nufarm.com or www.far.org.nz, or talk to your agronomist.