Two of the keys to slowing the development of herbicide resistance are reducing escapes and avoiding unnecessary chemical use.
Ideally, everyone should aim to target specific weeds with the most effective modes of action efficiently applied – in rotation, of course – at the lowest label rate that will achieve excellent control, says BASF’s cereal portfolio manager Roger States.
He said Group 27 chemistry is commonly included in many post-emergence spray programs in cereal crops, but usually as part of a co-formulation that includes either MCPA (for example Precept) or bromoxynil (e.g. Velocity and Talinor).
“Obviously those co-formulations lock in a fixed ratio between the Group 27 active and its partner chemical – one that may not be the most effective blend to control particular weeds in specific scenarios.”
Frequency from BASF offers growers a more flexible alternative that can be tailored for optimum control of whichever weeds emerge. Frequency has a unique Group 27 HPPD inhibitor active – topramezone – that can be tank-mixed with either LVE MCPA or bromoxynil at appropriate rates.
As a next-generation HPPD inhibitor, Mr States said topramezone has the same mode of action as the older products but works far more efficiently. Whereas Frequency’s single approved application rate – 200 mL/ha – delivers just 12 g/ha of topramezone, Velocity’s highest label rate – 1 L/ha – delivers over three times as much pyrasulfotole (37.5 g/ha).
“The added advantage is that Frequency’s tank-mix partners can be used at their lowest effective label rates for the applicable weed stages and species to make sure there is no superfluous chemical use.
“This is a relatively low-key innovation compared to some of the more ground-breaking products like Luximax and Voraxor that we’ve introduced in the last few seasons.
“Trial work has shown that Frequency, with the right tank-mix partner, provides excellent control of hard-to-kill broadleaf weeds like fleabane, sowthistle, buckwheat, wireweed, wild radish, bifora and capeweed.”
Mr States said the same work has also shown the value of that ability to tailor the tank-mix to the target weed species.
“If bifora’s a major issue, you’d definitely want to add bromoxynil rather than MCPA. But if fumitory’s the main problem weed, you’d have to go the other way and use MCPA.
“Capeweed and wild radish are also more susceptible to the Frequency and bromoxynil tank-mix.”
As well as the opportunity to switch mix partners, Mr States said growers will appreciate being able to adjust the rates to suit the weed control challenge.
“Frequency is registered for most weeds up to the 6-leaf stage.
“If you’re spraying weeds that are up around that 4–6-leaf mark or from the really hard-to-kill species, you can ‘dial up’ the bromoxynil or MCPA rate to get the best result.
“We can provide growers and advisers with detailed advice about the preferred mixes and rates for a whole range of weed infestations. Within those general parameters of course they’ll soon find out exactly what works best for each weed challenge in their particular paddocks.”
The primary benefit of Frequency’s flexibility when it comes to managing resistance is that all the tank-mixes growers apply can be tailored to work with maximum efficiency.
Mr States said here should be less active ingredient applied to smaller weeds and the more potent mixes applied to larger weeds will limit the possibility of escapes. A further benefit is that a full dose of both Frequency and the mix partner can be applied to weeds with a high resistance risk, applying WeedSmart principles to maximum effect.
“Like the other Group 27 herbicides, Frequency will mainly be used against broadleaf weeds. However it has a surprising ‘bonus’ registration for suppression of Avena sterilis seed-set in northern NSW and Queensland.
“Many growers in the south and west may not realise that there’s a second species of wild oats in Australia. Avena fatua is the dominant species in most areas, but Avena sterilis is much more common in northern cropping regions.
“Frequency’s activity on it is one of those quirks – like Voraxor’s additive impact on annual ryegrass – which remind us that even within the same chemical group every herbicide can have some surprising characteristics that set it apart.”
