Using residual herbicides beating fence line weeds resistance

Fence lines can be a haven for weeds, perpetuating one of the biggest threats to agricultural crops, however growers now have the opportunity to reduce this risk through the use of new herbicides offering long-term weed control.

Matt Willis, Market Development Agronomist with Bayer in WA, said weed resistance to herbicides has increased across agricultural areas and fence line weed management had been acknowledged as a contributing factor.

″Across broadacre and horticultural cropping areas, there has been increased resistance to glyphosate and paraquat (herbicides), as identified by groups like AHRI (Australian Herbicide Resistance Initiative) and Plant Science Consulting. Along fence lines, anecdotally there has been an increase in weeds surviving glyphosate, and it has become a strong focus for the GRDC and other research institutions in recent years,″ Matt said.

″Fence line weed control strategies have varied, but for the most part there has been an over-reliance on glyphosate and older triazine, sulfonylurea and imidazolinone chemistries. These products have been applied to large weeds in spring and often have not achieved effective control of those weeds prior to seedset.

″The seeds and weeds then end up in the adjacent crop, which can affect the profitability of the crop, particularly if the weeds are resistant to products such as glyphosate, which then impacts the weed control options in-crop.″

He said the lack of residual herbicide chemistry for use in combination with glyphosate and paraquat is believed to have led to increased levels of resistance to the herbicides, however more effective alternative mode of action herbicides with extended control had become available in recent times. Uragan^® (bromacil) has been an option over the last decade, Terrain^® Flow (flumioxazin) also has been used in recent years, and now a new pre-emergence option has arrived, Alion^® from Bayer.

Containing the active ingredient, indaziflam, Alion is a new Group 29 (formerly Group O) herbicide for controlling weeds along agricultural fencelines.

Video: Matt, Mitch and Tim assess the annual ryegrass numbers coming through 18 months after Terrain Flow was applied in combination with glyphosate in the fence line weed control trial near Jennacubbine in WA.

Matt said the pre-emergent herbicide was registered for control of a wide range of grass and broadleaf weeds and provided ″up to season-length control″. 

″The ability to use a different mode of action herbicide along fence lines compared to that used in-crop is a massive advantage for herbicide resistance management. Weeds haven’t developed resistance to indaziflam, so there won’t be survivors that get into crops and cause issues going forward,″ he said.

″Alion is also registered for use in tree crops and vineyards, which indicates it has sufficient safety to use alongside growing trees, and it’s an easy-to-handle SC formulation with a low application rate of 150 mL/ha.″

Matt said extensive trial work with Alion conducted by Bayer in recent years across Australia, including in different geographies and situations, had shown excellent results when compared against industry standards.

″Weed control and the length of residual control of weeds, which helps manage resistant weed populations, has been very consistent, and we have seen good safety on trees and vines.″

At Jennacubbine in the Avon Valley region of WA, Alion was included in a fence line herbicide trial featuring a large population of annual ryegrass, also of which was identified as moderately resistant to glyphosate, plus volunteer wheat, wild radish, capeweed and couch grass.

Treatments in the trial included Roundup UltraMax^® knockdown herbicide applied without residual herbicide, as well as applications in combination with Alion, Terrain Flow and Uragan to assess their weed control effectiveness. There also was an application of Alion with paraquat, instead of glyphosate, to determine if this knockdown herbicide was more effective against the prevailing population.

In terms of the length of activity provided by the residual herbicides, Matt said the Terrain Flow offered good control for five to six months before weed germinations occurred, whereas Alion and Uragan both provided season-length control.

″Eighteen months after the applications, weeds were coming through the Roundup treatment, as well as where it was applied with Terrain Flow. However, where the glyphosate or paraquat was combined with Alion or Uragan, there was still good control and, consequently, bare earth.″

″The trial showed that using effective residual herbicides helped to control herbicide-resistant weeds – in this case, the glyphosate resistant types, because it controls the plant at emergence. This stops the resistant weed from setting seed and further adding to the seed bank and the potential to spread back into the crop. By also not setting seed along the fence line and germinating over summer, growers can apply herbicides 12 months later, to bare earth and small weeds, as opposed to larger weeds.″

He said using alternate mode of action, residual herbicides like Alion, rather than those currently used along fence lines and in-crop, would be an effective long-term strategy to keep fence lines weed-free and for management of herbicide-resistant weeds.

There already is strong industry interest in the use of Alion for fence line weed control.

″Using alternative mode of action herbicides to those currently being used is always something that gets people passionate and excited, and we are seeing that with the interest in Alion,″ Matt said.

For further information on Alion and its effectiveness in trials across the country, growers can contact their local Bayer representative.

Alion^® and Roundup UltraMax^® are Registered Trademarks of the Bayer Group.