With developing herbicide resistance and limited products registered for use, controlling wild radish in oats has been challenging for Western Australian growers, but a trial in the southern wheatbelt has highlighted some new control options.
The trial, coordinated by Elders Narrogin agronomists Helen Wyatt and Brett Jenkinson, examined the efficacy of different wild radish herbicide control options in oats, as well as their crop effects.
Helen said wild radish control in oats had become more difficult with herbicide resistance, limited registered products and different target markets.
She said there had been much discussion as to which products were best, the impact of crop phytotoxicity (if any) on yield and the need to rotate modes of action.
“In the past, Tigrex has been the go-to product on grain oats and Bromicide® MA or straight LVE MCPA on hay oats to ensure colour in the final product is not compromised,” Helen said.
“With newer products like Precept® now registered in oats, we thought it worthwhile investigating where they fit in the oat production system.”
The selected trial site at Wandering had a radish population varying from 50 to 200 plants/m², with the largest at the five-leaf stage, and was sown with Bannister oats, which were at early tillering.
The site was sprayed on June 15th during the 2016 season using the Bayer Application Trailer with a water rate of 80 L/ha, and applications included Bromicide, Paradigm®, MCPA Amine, Flight®, Tigrex, Precept, Broadside®, LVE MCPA and 2,4-D Amine applied at a later timing.
Helen said that while conditions weren’t ideal when the site was sprayed, there were still some clear performers when it came to analysing the results.
“Precept was a standout product. Although very slow to control weeds early-on due to the conditions at application, it was one of the best treatments in the end,” Helen said.
“The spraying was done late in the afternoon and it was quite an overcast day, which had an impact.”
To maximise efficacy of Precept, it should be applied during the day, at least one hour before sunset.
“Final crop yield was highest in the Precept treatment, which also highlighted the crop safety of this newer herbicide mode of action,” Helen said.
Precept, from Bayer, uses a combination of pyrasulfotole and MCPA LVE, with pyrasulfotole being the only Group H active ingredient registered for use in cereals.
It controls a wide range of broadleaf weeds and is effective against wild radish resistant to Group B, C and F herbicides.
Precept also provides excellent crop safety in oats and can be applied from the three-leaf stage through to first node of the crop.
Helen said Flight and Tigrex both had the quickest early control of the radish, but both had lower crop yields and it was difficult to determine if that was due to crop phytotoxicity.
She said both of those products contained diflufenican and showed the most crop phytotoxicity of all products used.
Broadside and Bromicide were slow to kill weeds and struggled on larger plants, which resulted in a lower overall control.
“The late 2,4-D Amine strategy is one that farmers traditionally used for late radish control when populations were only just developing, as it prevented any late subsequent germination in crop,” Helen said.
“Over time and with increasing radish populations, spraying earlier has seen improved weed control and yield increases, as it removes early crop competition.
“Weed control and yield were improved compared to the untreated control using this strategy, showing a late application is better than nothing, although still not ideal.
“All earlier single treatments gave a better yield result than a single late 2,4-D Amine application.”
Herbicide resistance test kits, provided by Bayer, were used at the site and found both Group I and F resistance developing in the radish population.
Helen said Group B resistance was not identified, but some level was assumed to be present.
She noted that during the trial, Paradigm, which uses both Group I and B modes of action, was also quite slow to kill weeds and struggled to control bigger plants, while LVE MCPA was very slow to kill larger weeds, but maintained a good crop yield.
“Given the developing Group I resistance in this location, LVE MCPA is not the preferred treatment option going forward, but the knowledge that it is still achieving some level of control will be useful in certain scenarios,” Helen said.
“There’s a lot of growers in this area that haven’t tested their weeds for herbicide resistance and just continue to use the same control methods, but I think they would probably be surprised at the level of resistance they do have.
“Hopefully the results of this trial get growers thinking about rotating their chemistry and modes of action, and Precept is a newer herbicide that we’re trying to introduce, especially given its flexibility with oats.”
Feature image: Elders agronomists pictured assessing weed control in the herbicide trial in oats at Wandering
Image provided by Bayer