Trials of new, alternative mode of action herbicides against grass and broadleaf weeds along fence lines are demonstrating safe, long-term control of these weed populations, also providing a breakthrough in herbicide resistance management.
Bayer SA-based market development agronomist Tim Murphy said across many farms, fence lines provided a good bridge for weed seeds to move into paddocks along with a green bridge for harbouring pests and disease - existing management allowed potential for resistance development.
“Many growers traditionally look to control fence line weeds after seeding has been completed and quite often, they will use some knockdown herbicide left in the shed, perhaps with some pre-emergent herbicide, or they may use a pre-emergent herbicide with longer control,” Mr Murphy said.
“However, they may still be looking at the same mode of action that they have used in the paddock.”
With alternative mode of action, pre-emergent herbicides now available and offering long-term control, he encouraged growers to consider them to allow a different mode of action to be used along fence lines to help break the bridge and limit resistance development.
Mr Murphy also urged growers to undertake fence line weed control earlier in seeding programs, or even prior to seeding, to reduce potential for resistance development.
“When knockdown products are applied to larger, more established weeds later in the season, we see there is often a reduced level of control and that increases potential for resistance developing and moving from fence lines into paddocks.”
In recent years, Bayer has been conducting fence line trials with its new Alion pre-emergent grass and broadleaf weed residual herbicide throughout Australia. Mr Murphy said ideally, it would be used before weed germinations and seeding where it remained on soil surfaces for up to four weeks before rainfall incorporation.
If weeds are present it should always be applied with a knockdown herbicide.
Containing the active ingredient, indaziflam, Alion is a Group 29 (formerly Group O) herbicide, allowing an alternative mode of action chemistry to be used along fence lines compared to that commonly used in paddocks.
“That is its key strength, while it’s also a nice, low dose formulation applied at 150 mL per hectare, it’s very compatible with pretty well all knockdown products currently used in the industry, and it has a sufficient margin of safety when applied near trees, allowing you to apply it along all fence lines,” Mr Murphy said.
Trials across the country have shown long-term control of grass and broadleaf weeds.
Mr Murphy said an exceptionally long-term trial at Birdwood in the Adelaide Hills, on an existing weed population, has compared Alion applied at 150 mL/ha with Roundup UltraMAX at 2.5 L/ha alongside an industry standard, Terrain Flow, applied at 730 mL/ha with the same rate of Roundup UltraMAX.
He said a unique aspect of the trial was we had some perennial and annual grasses, so it has given us a good view of what Alion will do against all species along the fence line.
“Another interesting point is that the Alion sat on the surface for about three weeks before around 12 mm of rainfall was received to incorporate it.
“What we saw after the rainfall was initial flushes of grass and broadleaf weeds and they were quickly controlled as they emerged. We saw that result through the whole growing cycle as weeds germinated following rainfall events,” he explained.
The trial is now well into the second year.
“We’re starting to see some weeds emerge in all treatments, but the Alion plots are still relatively clean, which is showing that depletion of the weed seed bank and the long-term residual control that it provides.
“In the Terrain Flow industry standard treatments, weeds started to come through after the nine-month period, with the perennial grasses dropping seeds for the season to come, whereas the Alion plots had very few weeds coming through.
“It probably would have been good to apply another knockdown in the Terrain Flow treatments earlier to top-up the pre-emergent herbicide, but we stretched the timing out to assess the long-term control from each herbicide and Alion is still providing a nice reduction of that seed bank. We’ve seen very little seed-set come through and it’s going to go on and provide great length of control.”
Mr Murphy said the Birdwood site features a heavier soil type, which along with good rainfall through the Adelaide Hills, added to the strong length of control from Alion. Other trials on lighter soils have shown slightly shorter weed control of around nine months plus.
Heading into winter he expects weeds would emerge in all treatments but there could be less in the Alion plots because it has depleted the seed bank beautifully.
Growers who viewed the Alion trials were impressed with the ability to apply an alternative mode of action herbicide along fence lines from that widely used in-paddock, as well as with the low-dose, easy-to-use formulation and its safety on trees, allowing it to be used along all fence lines.
Mr Murphy said an effective, long-term fence line weed control strategy with Alion could include two years of applications at 150 mL/ha, before rotating to perhaps a knockdown product or introducing alterative mode of action treatments and other long-term industry standard pre-emergent herbicides in the third year.
