Phenoxies continue to find their place in weed control

Although they have been around a long time, the selectivity of phenoxy herbicides, value for money and role in resistance management mean they are still a force to be reckoned with.

At a global level Nufarm is one of the key players in the production of phenoxy herbicides. Two key phenoxy manufacturing plants operate in Europe, situated in Linz, Austria and Wyke, West Yorkshire, UK.

The term phenoxies is an umbrella title for a group of herbicides that mimic the effect of natural plant hormones known as auxins. Auxins are only found in plants and regulate growth; one of their functions is to make the plant grow towards the light.

Phenoxies such as MCPA, CMPP-P and 2,4-D mimic auxins’ mode of action causing the target weed to thicken and twist, effectively neutralising it. These actives are selective in grass and cereals plus a range of additional crops across Europe. A group of phenoxies – butyrics (2,4-DB/MCPB) – are also selective in many clovers and legumes.

Both at a global and European level, Nufarm says it continues to invest in the widest portfolio of phenoxy active ingredients in the industry.

Why does Nufarm invest heavily in phenoxies? Because even though it has been more than 70 years since 2,4-D was discovered, Nufarm believes they are an essential group of products, now more than ever, as herbicide resistance becomes more of an issue.

Phenoxies are still used today in a wide range of crops and offer flexibility to the user. For example, they can be used solo for control of specific weeds such as thistles in grassland. They can also be formulated into products containing two or more phenoxies to be used for broad spectrum control in crops such as spring cereals, and they can also be beneficial components in tank mixes.

Cost effective

This group of herbicides is said to provide a cost-effective solution for growers and agronomists.

The demise of several active ingredients in recent years has left fewer options for broad-leaved weed control in cereals. The lack of new herbicide modes of action, combined with a heavy reliance on sulphonylureas in winter and spring cereals has led to the development of ALS resistance in some broad-leaved weeds. In the UK, confirmed cases of broad-leaved weed resistance are increasing year-on-year where weed control has relied upon the use of sulphonylureas.

Phenoxies can provide an alternative mode of action, helping with resistance management.

A spokesman from Nufarm says: “Because phenoxies mimic the plant’s natural growth system there is very little resistance to them. As a result, they can affect a wide range of weeds without resistance developing.

Timing and tank mixes

For cereals, in most cases the cut off spray timing is at growth stage 31-32, to minimise the effect on the ear and maximise yields.

Phenoxies, combined with sulphonylureas in tank mixes can provide a wide spectrum of control over broad-leaved weeds. Adding fluroxypyr or florasulam to the mix adds cleaver control. In grassland, phenoxies combined with fluroxypyr boosts dock and chickweed control.

Timing a phenoxy application in grassland means spraying when weeds reach the leafy rosette growth stage during spring or leafy growth post-cutting in summer and autumn.

The weeds must be actively growing for the phenoxy to translocate through the plant.

“Phenoxies have not been used over-excessively – the fact they have been used for so long is testament to the fact that they still work.”

Nufarm is in the process of renewing approval of all the phenoxy active ingredients and their relevant products to ensure these solutions are available to customers and meet their changing needs.