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Wherever grassweeds are an issue cereal growers need to put as much care and attention into stubble treatment ahead of their crops as they do into their T2 fungicide spraying, insists Agrii regional technical adviser and spraying specialist David Felce.

“The most effective pre-planting control is a crucial part of managing black-grass, ryegrass and brome these days,” he pointed out. “And you only get one or two shots at it.  So you really need to make your stubble spraying count by ensuring it’s as effective as it can be.


“As well as using the right rate of a good glyphosate with the right adjuvants where they’re needed, this means timing your applications right; using the right water volumes, nozzles and pressures; and employing the best spraying practice.”


If there’s one piece of advice David has for getting stubble spraying right this autumn it’s ‘don’t rush’. Too often he finds people don’t have enough patience to wait for a decent weed flush before going in with the sprayer.  In his experience too, many don’t spend enough time ensuring the right glyphosate rate for the job, balancing it with sufficient water conditioning, and matching water volumes, nozzles and spray pressures. At the same time, they frequently spray too fast and with too high a boom height for the best weed targeting.


“You’re on a hiding to nothing trying to reduce the sort of black-grass seed banks so many fields have by spraying-off repeated stale seedbeds as soon you detect the faintest hint of a weed flush,” he said. “This is unlikely to make any significant dent in most populations. Instead, at Stow Longa we’ve always found the best approach is to set-up and spray-off one or at most two stale seedbeds ahead of planting, then keep the rest of the seed bank asleep with the least possible soil disturbance at drilling. This is supported by the latest Roundup research showing that 2-3 leaves is the optimum timing, with the most effective control achieved from two applications. 


“My starting point for stubble control is always 540g of glyphosate per hectare and if I’m holding-off longer and using a single pre-planting application my default rate is 720g/ha to ensure the best possible kill of larger plants and put the least pressure on resistance development.


“Adjuvants should never be used to replace glyphosate levels,” stressed David Felce. “However, they can be very valuable where either the pH or hardness of the water is an issue.  Ammonium sulphate is useful to acidify your water but of limited value if it’s too hard; in which case you need to use a cation-complexing conditioner before adding the glyphosate to the tank.

“Using the right adjuvant is especially important with generic glyphosates,” he added.  “However, our trials show worthwhile improvements from water conditioning even with premium formulations. They can also be useful in reducing drift from flat fan nozzles where the most modern, low drift formulations like Roundup Powermax aren’t being employed.”


Although glyphosate works well with the coarse droplets that minimise drift, David Felce considers it important that stubble sprays aren’t too coarse as this limits droplet numbers, reducing coverage and the chance of hitting all the targets; especially the small, thin leaves of seedling grassweeds.

For this reason he recommends flat fan rather than air induction nozzles, with a careful balance between spraying speed, water volume and nozzle choice to achieve pressures of between 1.5 and
2.5 bar.

“I like to see forward speeds of 10-12 km/hour with a boom height of around 50cm to minimise the turbulence which can seriously compromise targeting and increase the risk of drift,” he noted.  “Water volumes of 100 litres/ha work best, giving you higher concentrations of glyphosate on the leaf and allowing you to cover more hectares in a day.

“At 12km/hour and 100 litres/ha, 03 FF nozzles will operate at a very effective 2.0 bar, while 025 FFs at the same water volume will require a 10km/hour spraying speed to keep to 2.0 bar. Higher speeds here will push pressures up to 3.0 bar, producing sprays that are too fine. If you can’t drop the boom down as low as 50cm, you should replace the standard 110o flat fan with an 80o nozzle for the right spray quality and coverage.”


As well as keeping spraying speeds and boom heights down, David Felce suggests sprayer tyre pressures at the lower end of the recommendation to act as shock absorbers and help improve boom stability, so maximising targeting and minimising drift risk.


He also insists it’s vital to read today’s glyphosate labels carefully, as different formulations can vary quite widely in their where and how they can be used; especially in areas like post-planting, pre-emergence use which he has found to be very valuable wherever drilling is delayed by more than a few days after stubble spraying.