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Herbicide hits to raise maize yields

Agronomy Issues
16.04.2020
Maize drilling

New recommendations for maize herbicide applications this season are looking to capitalise on extensive trials with 90% drift reduction technology (DRT) for pre-emergence treatments.

Syngenta Application Specialist, Scott Cockburn, advocates that whilst in perfect spraying conditions the company’s 3D Nozzle will achieve the optimum results, if conditions are compromised in any way, new 90% DRT nozzles can maintain a more consistent spray deposition on the surface and give better results. 

Scott Cockburn

“Pre-emergence treatments are particularly valuable in maize crops to get plants established quickly in a clean seedbed,” he advised.

“That gives greater flexibility with follow-up post-emergence application timing and options, targeted at the fields’ specific weed spectrum before damaging effects of competition.”

Importantly, spring cropping of maize gives growers a chance to get on top of some problem grass-weeds. Dual Gold contains an alternative mode of action to those available in cereals and trials have shown some useful activity on black-grass.

Weed free maize

Scott recommends growers prioritise fields particularly badly affected with difficult grass weeds when spray conditions are optimum for pre-emergence treatments. “That gives the best opportunity to use the 3D Nozzle to maximise results.

“But if spraying conditions are compromised, and for all other applications, the preferred option would be a 90% drift reduction nozzle,” he said.

90% drift reduction nozzles for pre emergence application

He reported Syngenta UK application research has shown 90% DRT nozzles, operated at a water volume of 200 l/ha, delivered consistently better pre-emergence weed control across a range of conditions, compared to conventional flat fan nozzles.

“The key advantage of 90% nozzles is not only the reduction in drift to ensure more product stays on the target, but also the ability to retain the spray pattern and consistent coverage in gusty wind conditions.”

In the trials, with a wind speed averaging an ideal 1.6 m/sec (5.8 km/hr), gusts were recorded between 0.2 and up to 8.6 m/sec (30.1 km/hr). 

Furthermore, results from two years’ trials had also shown a 25% improvement in weed control from applications at 12 km/hr, compared to 16 km/hr. The slower speed is also a factor in helping to maintain an even boom height, of 50 cm above the target soil surface.

“Maintaining slower speeds, along with nozzle size selection, typically enables delivery of the required water volume at lower pressure, which minimises drifty fine droplets and increases the proportion of large droplets that better hit and cover the soil surface,” he added. Trials showed results were consistently better at 200 l/ha, compared to 50 or 100 l/ha, with no significant enhancement from increasing to 400 l/ha.

Post-emergence options

For post-emergence applications in maize, Scott again recommended the use of 3D Nozzles at the early stages of crop growth and when application conditions were good. “Ideally growers should be targeting weeds before the crop reaches the four true leaf stage, to avoid the most damaging effects of competition.

“Later application can result in serious reduction in crop yield and the feed value of maize silage, for livestock or anaerobic digestion.”

Maize research trials results over three seasons had shown the early removal of weeds, at the crop’s two to three leaf stage, gave an average 4.3 t/ha yield advantage (+ 20%), compared to delayed removal at the four to six leaf stage. That was calculated to be worth around 6650 litres of milk per hectare over the trial period, or more than 1420 m3 of methane yield from an AD plant.

maize ration

“Early application also ensures weeds are more easily targeted with Callisto, or Callisto + Milagro. The 3D Nozzle, fitted with their angle alternating to face forward and backward along the spray boom, has been shown to give the best all round coverage and retention of herbicide on small weeds,” he added.

However, if conditions were to be compromised and spray drift was of any concern to operators, they should switch to the coarser droplet of an Amistar nozzle. Scott also highlighted that, as the crop grows and begins to cover between the rows, the Amistar nozzle can also be more effective at targeting small weeds.

“There can be the temptation for operators using the 3D Nozzle to increase sprayer pressure to push the droplets down through the canopy to reach smaller weeds. But counter-productively that can create more fine droplets that will be intercepted by the crop, or worse still, be lost as drift." Illustrated below.

Fine droplets intercepted by larger leaves

“The better option is the larger droplets from the Amistar nozzle, operated at 2-3 bar, that will give good coverage of the weeds and minimise the risk of drift."

Watch the Spray Dudes explain the principles of optimum application to target early post-em herbicides

“A sequence of pre- and post-emergence herbicide, along with selecting the appropriate application techniques, will help to maximise maize yields, as well as its value to reduce weed populations through the rotation,” Scott advised.