Kill more grassweeds with your stubble sprays

stubble spraying

© Tim Scrivener

Avoiding the use of air induction nozzles and going no faster than 12kph will enable growers to take out more troublesome grassweeds on stubbles prior to drilling crops this autumn.

For growers with a bad blackgrass problem, stubble applications are the most important sprays of the season and getting it right takes the pressure off pre-emergence and post-emergence herbicide applications.

“With time at such a premium and effective control of blackgrass and other problematic weeds ahead of drilling so crucial, less-than-ideal pre-planting glyphosate treatment is something farmers cannot afford,” says Monsanto’s Roundup technical specialist, Barrie Hunt.

See also: Guidelines aim to prevent glyphosate-resistant weeds

“Quite apart from wasting time and money, and putting extra pressure on hard-pressed pre- and post-em chemistry, an incomplete kill is the fastest route to resistance development,” he warns.

“You’ve only got one or two shots to tackle blackgrass ahead of drilling,” adds Agrii regional technical adviser and spraying specialist, David Felce.

So it makes sense to take the time and effort to get your glyphosate application spot on, he says.

Hitting the target

Correct glyphosate targeting is as important as timing in Mr Felce’s opinion. He is adamant that operators need to spray at the right speed, height and pressure with the most appropriate nozzles as well as using the correct rates and water volumes.

“When workloads are stretched, as they tend to be in the autumn, it’s tempting to crack on with stubble spraying at 14-16km/hour with the boom set high enough to ensure good ground clearance and coarse or air induction nozzles to minimise drift risk,” he says. “In my experience, water volumes as low as 100 litres/ha are fine. They allow you to cover more hectares in a day and get higher concentrations of glyphosate on to the leaf.

Nozzle choice

“In view of its translocated action, in line with traditional glyphosate guidance, I would normally recommend a relatively coarse spray in the interests of drift reduction.

“But with small, thin seedling blackgrass leaves, the spray shouldn’t be too coarse as this limits droplet numbers, reducing coverage and your chances of hitting all the targets.”

For this reason, Mr Felce advises against using air induction nozzles. Instead, he sees 03 flat fan nozzles operated at 2.5 bar as the best all-round option.

Boom height

For the most effective seedling weed targeting and least drift risk, he advocates a boom height of around 50cm and forward speed of 12kph to minimise turbulence.

Where it’s difficult getting the boom down to this level, he suggests replacing the standard flat fan 110 with an 80deg nozzle to ensure the right spray quality.

Applying in the wrong conditions can also hamper success. For example, Mr Hunt says applying in hot and dry weather, or when rainfall occurs within a few hours of spraying or using hard water can compromise glyphosate uptake and activity.


“It’s equally important to use the right rate of glyphosate for the job,” he says.

“You typically need 540g/ha of glyphosate to control grassweed seedlings of up to six tillers and up to 1,800g/ha for the most difficult perennials. In most situations, adjuvants will not make up for any lack of active ingredient,” says Mr Hunt.