Esperance trial reveals radish resistance

Last season a trial run by Farm and General assessed different herbicides and mixes for effective wild radish control and found evidence of developing resistance in the area.

Farm and General senior agronomists Andrew Heinrich and Monica Field conducted the trial, supported by Bayer, with help from Bayer customer advisory representatives Craig White and Rick Horbury.

According to Mr Heinrich, the trial site at Nerridup had a history of wild radish problems and they suspected a level of phenoxy tolerance was present in the population.

“It’s been a problem paddock for a while and the radish population is quite large, so we were looking for options to control it in the cropping phase,” Mr Heinrich said.

“The paddock comprised non-wetting sandy soils and it was important for us to get residual control of subsequent germinations.

“Previously we have relied on 2,4-D or MCPA LVE for controlling wild radish, without getting satisfactory results.”

Using a spray trailer similar to Bayer’s Applicator Trailer, Mr Heinrich said they applied herbicide products and mixes including Velocity, Precept, MCPA LVE, Tigrex, Jaguar, MCPA LVE/Logran, Flight, Velocity/MCPA LVE, Velocity/Tigrex, Precept/Jaguar and Precept/metribuzin.

The wet start to the season ensured a good germination of wild radish.

Mr Heinrich said the conditions meant it was likely seeds emerged from the seed bank that had been dormant for a long time.

The paddock was sown with Mace wheat, which was at five-leaf to early tillering at the time of application, with the wild radish population measured at an average 30 plants per square metre, ranging in development from cotyledons up to eight-leaf stage.

“We use a spray trailer based on the Bayer Application Trailer, which allows us to mix up to nine different treatments and spray out a combination of three at one time,” Mr Heinrich said.

“We can lay-out trials relatively simply and quickly.

“With this trial, we looked at the knockdown and scored the applications out to 65 days, although we didn’t take the individual plots through to yield.

“We stayed at the top end of application rates and as we suspected MCPA tolerance, we went in at 1.5 litres a hectare, which is a lot higher rate than most farmers would be using.

“All the treatments gave us good to excellent control.

“Most of the mixes gave a good burn down of existing radish, particularly Precept and Velocity, which had good coverage of the leaves.”

Precept, from Bayer, uses a combination of pyrasulfotole and MCPA LVE.

Pyrasulfotole is 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.

Velocity, also from Bayer, uses the active ingredients pyrasulfotole and bromoxynil and is registered for use in wheat, barley, triticale and cereal rye.

It can be applied from the two-leaf through to fully tillered stages and is effective against broadleaf weeds that have developed resistance to herbicides containing Group B, F or I active ingredients, such as metsulfuron, diflufenican, MCPA, 2,4-D and others.

Mr Heinrich said their fears were confirmed when it came to the results from the MCPA LVE application.

“MCPA LVE showed some survivors 28 days after application,” he said.

“We saw a slightly better result with the MCPA/Logran mix, but there were still some surviving plants.

“So, as suspected, there is some tolerance in the population.

“Velocity and Precept products achieved much better control, while having something such as Tigrex, Jaguar or other products containing diflufenican, was good value as the residual control picked up subsequent germinations before they became a problem.”

While they didn’t assess the yield results, Mr Heinrich said they did find there were still plenty of effective options for growers when it came to wild radish control.

He said there was no need to keep relying on the same modes of action and risk developing resistance.

“We want growers to be mindful of resistance and pay attention to the level of control they are actually getting from their herbicides,” he said.

“Just because you can’t see radish popping out the top of the crop, doesn’t mean it hasn’t managed to set some seed.

“What we find is that when you get those early stages of tolerance developing, the plant survives and manages to set seed every year, building up the seed bank.”