As herbicide resistance to ALS chemistry continues to grow in broadleaf weeds and the recent warm weather threatens to create a flush of growth, it could be time to consider alternative control options. However, with so many different products and actives available on the market, finding the best solution can prove to be a difficult task. CPM investigates.

Despite originally being launched in the early 1950s, phenoxy herbicides are a potentially under-used tool in the spray armoury. But what exactly are they? And how can they benefit growers?

Phenoxies describe a group of herbicides which mimic the effect of natural plant hormones – auxins, explains Daniel MacDonald, agronomy manager at Nufarm.

“They imitate the plant growth regulator indol-3-acetic acid (IAA), which controls cell enlargement, division and development throughout the plant’s life cycle; it over-stimulates plant cells causing abnormal plant growth and subsequent death.”

The phenoxy group includes MCPA, 2-4 D, CMPP-P, 2,4-DB, MCPB, and 2-4 Dichlorprop-P, all of which are well tolerated by spring and winter cereals: It is even possible to apply MCPA up to GS39 in wheat.

So how exactly do they work? Following application, leaf absorption occurs within four to six hours and concentrates within the plant’s actively growing regions – the meristematic tissue within the stem and roots, says Dan

“The phenoxy interferes with the plant’s metabolism, protein synthesis, cell division and nutrient transportation within the plant which has no mechanism to control the concentrations of these imposters. It is recommended to use them in combination with sulphonylureas in tank mixes to provide wide spectrum control.”

When it comes to resistance management, these age-old herbicides could provide an alternative option to traditional ALS chemistry when it comes to tackling broadleaf weeds this season, adds Dan.

“Phenoxies could have a significant role to play going forward in managing resistance because they have the lowest risk of fostering resistance development.

“Introducing phenoxies to postpone resistance will lengthen the time before resistance-prone herbicides become truly non-renewable.”

 

Top tips for best use:

  • The weed must be growing actively
  • Avoid cold, frosty conditions
  • Phenoxies need around four to six hours without rain to get into the plant
  • Check weed species susceptibilty
  • Get the spray timing right – ideally, targeting young plants which are not too small to avoid droplet bounce
  • Ensure the crop isn’t under any stress from poor nutrition, drought or disease as weed control will be reduced and could potentially damage the crop

For more information on phenoxy herbicides and how you could potentially benefit from them, visit: https://cdn.nufarm.com/wp-content/uploads/sites/9/sites/26/2018/12/10161508/Nufarm-Phenoxy-Guide-A4.pdf