Farmers preparing to tidy up stubbles with glyphosate this spring are reminded to avoid applications to stressed weeds, which can otherwise reduce glyphosate efficacy.

Applications to stressed weeds – particularly those sat in waterlogged soils – at this time of year can restrict the translocation of glyphosate throughout the plant.

With prolonged bad weather causing difficulties last spring and the reported glyphosate resistance case in Italian ryegrass, Bayer agronomist Roger Bradbury underlines the importance of correct application and stewardship.

See also: First case of glyphosate resistance confirmed on UK farm

“Effective weed control from glyphosate depends on suitable application conditions.

“Last spring stretched the limits, reminding us glyphosate is not infallible.

“Several factors combined to affect performance, and these are things to watch out for this spring,” says Roger.

Spray rate

First, Roger recommends use a sufficient spray rate that reflects the hardest-to-kill weed in the spectrum and those at more advanced growth stages.

“If there is a delay between spray recommendation and application, double-check weed size and consider a higher rate if weeds have grown,” he says.

Spray windows and setup

Last spring, spray windows were few and far between, meaning some farmers made applications in marginal conditions or at speeds well in excess of 12km/hour to cover the ground.

Spray operators should pay attention to nozzle choice, boom height and calibration.

If a water conditioner is deemed necessary, make sure this is added to the spray tank first.

“Should the weather become more challenging, keep in mind that modern Roundup formulations are faster-drying and deliver more reliable and consistent levels of efficacy even under more difficult conditions.”

Avoid regrowth

In later spring, be aware that weeds at the stem extension phase of growth are often difficult to control.

The glyphosate is carried upward controlling the shoot, but is not translocated sufficiently to the roots so there may be regrowth.

“Allowing plants that regrow to set seed is a resistance risk.

“The danger was underlined by the resistance announcement earlier this year.

“Ideally, avoid regrowth situations by not applying at stem extension.

“But, if you notice regrowth, destroy the plants, preferably with a mechanical or chemical alternative to glyphosate.”