As concerns around herbicide resistance continue, CPM looks at how an age-old tool in the armoury could provide an alternative solution to more popular chemistry this season.

By Charlotte Cunningham

ALS herbicide resistance is on the rise, with a recent survey conducted by CPM and Nufarm highlighting that 79% of growers thought resistance management was an important part of their strategy.

There are a number of ways to combat ALS resistance in cereals, such as extending rotations and crops, however, one of the most important is to alternate modes of action used in the herbicide programme. While new active ingredients are few and far between, this year growers could benefit from making greater use of a herbicide group which has been on the market for quite some time, says Daniel Macdonald, agronomy manager at Nufarm.

“Following a mild winter carrying through into spring, growing conditions have been good not only for crops but for weeds too. Cleavers, red dead-nettle and poppies among others are easy to find within winter-sown crops and phenoxy herbicides could be the answer.”

There’s nothing new about phenoxies; they’ve been commercially available for over 70 years and remain among the world’s most widely used herbicides. “Phenoxy chemistry mimics the effect of natural plant hormones called auxins. They are formulated from acids, normally as salts and sometimes, as esters for cost effective broad spectrum weed control in cereals,” he adds.

The phenoxy group includes MCPA, 2-4 D, CMPP-P, 2,4-DB, MCPB, 2-4 Dichlorprop. They can be combined with each other and with other broadleaf weed herbicides such as sulfonylureas or florasulam in tank mixes to provide wide spectrum control of broadleaf weeds. “Phenoxies are well tolerated within a range of crop growth stages, both for winter and spring cereals with just one or two foliar applications; it’s possible to apply MCPA up to GS39 in wheat and spring barley GS31 whilst CMPP-P is flexible up to GS33 in winter cereals.”

Despite the proven efficacy and availability, CPM/Nufarm’s survey found that a third of respondents hadn’t used phenoxy chemistry in the last five years – the majority either weren’t aware of their benefits in resistance management or hadn’t heard of them. “Phenoxies have a significant role to play going forward in managing resistance because they have the lowest risk of fostering resistance development,” explains Daniel. “Introducing phenoxies to postpone resistance will lengthen the time before resistant prone herbicides become truly non-renewable.”

To find out more about how you could benefit from phenoxies, click here

Phenoxy cereal application timing

 

 

 

 

 

 

 

 

 

 

 

 

Top tips for phenoxy usage:

  • Weed must be growing. Avoid cold frosty conditions.
  • Phenoxies take about four to six hours rain free to get into the plant.
  • Check the weed species is actually susceptible.
  • Get the timing right – ideally young plants, but not very small to avoid droplet bounce
  • Make sure the crop is not under stress due to poor nutrition, drought or disease, otherwise weed control will be reduced and there is the possibility of damage to the crop.