Effective weed control from glyphosate depends on suitable application conditions. Farmers preparing to tidy up stubbles ahead of spring crops need to check the situation in the field before filling up the sprayer.

There were several cases of poor performance last spring due to prolonged bad weather. Added to that, the recent announcement of a resistance case in Italian ryegrass underlines the importance of correct application and stewardship

"Last spring stretched the limits, reminding us glyphosate is not infallible," says Bayer agronomist Roger Bradbury. "Several factors combined to affect performance, and these are things to watch out for this spring too."

Firstly, make sure the rate is sufficient for the hardest to kill weed in the spectrum and weeds 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.

Avoid applications to stressed weeds which may not translocate glyphosate throughout the plant effectively. Stress most likely means waterlogging at this time of year; drought or prolonged cold and frosty weather are the other possible causes.

"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.

"Apply with good applications technique paying 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.

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."

Mr Bradbury recommends farmers with Italian ryegrass populations be particularly vigilant. Research in the UK and experience around the world suggests that ryegrass species are higher risk with regards to glyphosate resistance. Stick rigorously to best practice for application and closely monitor performance in the field.