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On the trail of resistant weeds

A lack of moisture and managing herbicide resistant weeds are two critical challenges growers in the Victorian district of Donald need to manage well. As an Agronomist at Landmark Donald, Heath Griffiths knows those challenges only too well, particularly as he is also a local farmer.

A lack of moisture and managing herbicide resistant weeds are two critical challenges growers in the Victorian district of Donald need to manage well. As an Agronomist at Landmark Donald, Heath Griffiths knows those challenges only too well, particularly as he is also a local farmer. Heath produces wheat, barley, canola, beans, chickpeas and lentils on his 400 ha property, as well as providing agronomic advice to local farmers. 

“Rainfall is a big thing here, trying to conserve as much moisture as possible, and managing resistant weeds like annual ryegrass, wild oats, wild radish and mustard,” he says. 

“We’re trying to get on top of the rotation through chemistry, integrated weed management through narrow windrow burning and some people are also using sheep for grazing.” 

Heah says the resistance problems centre around ryegrass, as well as wild radish and thistles showing tolerance to Group B and Group C chemistry. He says the impact of resistance doesn’t just play out on the balance sheet in reduced yield, but also through the expenses incurred in weed control. This means strategies need to be adopted carefully, with Sakura®, a Group K herbicide from Bayer, playing a pivotal role. “We are finding Sakura has been doing a great job on really keeping the weed numbers down and it represents different chemistry. We always try to put it in a tank mix with trifluralin (Group D) or triallate (Group J) for increased protection and a different mode of action, to try and increase the longevity of Sakura.”

Having found good length of control with Sakura of between eight and 12 weeks, depending on moisture, Heath has been impressed with the chemistry. 

“It’s a good product. The protection it’s giving absolutely stands out – it’s as good as any pre-emergent chemistry I’ve ever seen,” he says. 

“We use Sakura in a lot of our wheat especially, ideally applying and incorporating it within three days of a moderate rainfall event. This approach gives us the best control. 

“Rotating into barley the following year has created a system which is going to allow us to hang onto this chemistry fora while.” 

The resistance issues facing Donald growers aren’t contained to just ryegrass, with wild radish also causing problems. “We’ve probably overused a lot of chemistry in the past – Group Bs are nearly gone on the radish and to a certain extent we’re probably seeing them become tolerant to Group Is also,” Heath says. 

“Rotating to Velocity® (Group H & C) and Precept® (Group H
& I) herbicides is giving us another string to the bow. They have been fantastic. Velocity especially is soft on the crop, so you can either come in early with that product, or alternatively you can use a Precept plus metribuzin (Group C) mix later, which gives us good control on big weeds as well.” 

He also has a keen eye on the future too, having been involved in trial work with Aviator® Xpro® fungicide from Bayer. Registered for use in canola and chickpeas, registration for this new chemistry in other crops such as lentils and barley is expected to follow. 

Heath says in 2016 they tested Aviator Xpro at different rates in lentils under permit to see what levels of ascochyta control it provides. 

“Ascochyta was a big issue in 2016 because it was so wet. It was just so prevalent in a lot of the lentils and chickpeas. Aviator Xpro just looks like it might be a little bit stronger and giving us a little bit more protection than previous chemistry, with an ability to apply it quite early,” he says.

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