WITH growing resistance from broad-leaved weeds to ALS herbicides, growers should consider phenoxies in the coming weeks, according to independent agronomy consultant, Keith Norman.

“With resistance to sulphonylureas (SUs) appearing in weeds such as chickweed, it is important not to let this situation drift,” he said. “It’s time we looked at supporting chemistry to SUs. We need phenoxies, they are both good value and effective; they are flexible in terms of timing; and they have been tried and tested for years.”

Nufarm’s Scottish agronomist, Iain Allan, agreed: “Phenoxies have traditionally been used with SUs for weed control in spring cereals and are a useful partner to broaden weed control and subsequently control chickweed and other SU resistant weeds.

“Furthermore, phenoxies still have a place in spring cereals that have been treated with a pre-emergence material since as many are weak on brassicas, polygonums and fumitory. Depending on the weeds present, a recommended solution is a phenoxy, such as High Load Mircam or Duplosan.

“Farms with SU-resistant chickweed, or very weedy crops, could consider a tank-mix of a phenoxy and fluroxypyr; this mix is extremely broad spectrum and complements most SU herbicides. I would recommend CMPP (Duplosan KV) for weeds such as chickweed, volunteer oilseed rape, Fumitory and speedwells, whilst a CMPP and dicamba mix will take out polygonums such as knotgrass and fumitory.”

Phenoxy chemistry is amongst the world’s most widely used herbicides and Mr Allan added: “It 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.

“However, despite their availability, Nufarm’s March grower 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. Introducing phenoxies to postpone resistance will lengthen the time before resistant prone herbicides become truly non-renewable.”

Mr Norman argued: “Since phenoxy herbicides are quite specific in the spectrum of weeds they control, it’s important for growers to double check what is covered by each of the options. Furthermore, since Clearfield oilseed rape varieties are securing a larger part of the market, there is also a need for alternatives to SU to keep volunteer weed resistance in check.”

Top tips for phenoxy use

• Weeds must be actively growing.

• Avoid applications in cold weather, less than 9°C degrees.

• Phenoxies take about four to six hours rain free to get into the plant.

• Check the species is actually susceptible.

• Get the timing right – ideally young plants, but not too 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.