Coverage counts for grass weed control

Pete Hawkins

Application technique can make a significant difference in achieving the best control of grass weeds with Axial Pro in wheat and barley crops this spring.

Where wet field conditions have delayed early grass weed applications, there is now an increasing mix of weed sizes - with some much larger overwintered plants, as well as  later spring germinating wild oats and ryegrass emerging, warns Syngenta Technical Manager and grass weed specialist, Pete Hawkins.

While NIAB research has shown weeds emerging from March onwards have a significantly lower impact on the crop and numbers of seeds produced, compared to over wintered weeds, if applications have been delayed or held back, it makes absolute sense to try and deal with as many of the small weeds along with targeting those earlier germinators. 

Watch NIAB advice on grass weed control  

Good coverage of Axial Pro on the grass weed leaf, along with warmer April temperatures and soil conditions for active growth, can now ensure better uptake of herbicide to achieve the most effective results.

Targeting grass weed herbicide applications in spring

Syngenta application research has shown where weeds may be shaded beneath the crop canopy, the best results can be achieved with a relatively coarse spray pattern, containing a higher proportion of large droplets, that are more effective at reaching weeds below. Applying in a water volume of 200 l/ha is also beneficial for aiding coverage throughout the canopy.  

Tackling larger grass weeds

With higher Axial Pro application rates of up to 0.82 l/ha being used to tackle larger grass weeds at later spring application timings, or for ryegrass treatment, just one or two droplets hitting a small newly emerged grass weed can be sufficient to give control. 

The modern formulation of Axial Pro ensures that even with larger droplets hitting the leaf, the drops burst and spread to ensure good retention and coverage on the surface of grass weeds.

Faced with trying to get the spray through a dense crop canopy, the natural inclination for operators may be to increase spray pressure. However, this would result in an increase in the proportion of fine droplets in the spray pattern that will be intercepted by the crop leaf – which would be counterproductive in penetrating through to small weeds below.

See how the Spray Dudes tackle grass weed application     

Spray Dudes show how to hit grass weeds in spring

While early spring applications, when grass weeds were openly exposed within the crop, would have been best applied using the angled 3D nozzles at 100 l/ha water volume, as the crop closes over, a switch to an Amistar nozzle at the higher 200 l/ha water volume has been shown to give better coverage through the canopy.

The larger droplet spectrum of the Amistar nozzle also offers better drift reduction, to maximise spraying opportunities and catch up on applications.   

Targeting grass weeds beneath the crop canopy


As applications move to later in the season, with the primary aim of treatments preventing grass weeds from setting seed and increasing populations, moving back to a 3D nozzle where conditions permit can help ensure optimum deposition on the target weed leaf exposed above the crop.

Axial Pro gives growers and agronomists a significant advantage for application right through to crop growth stage 41 (before flag leaf sheath extending stage) in wheat and barley, to target weeds later in the season where early control has not been possible. On these larger weeds it would always need to be used at the highest rates possible for the intended weed species.

Spray Assist App

The Syngenta Spray Assist App has been created specifically to help operators select the most appropriate option and operation of sprayer nozzles for any situation. Available to download free, it can be tailored for any farm’s sprayer set-up and provide instant answers for any application, as well as planning schedules to spray Axial Pro at the optimum timing.

Tank mixing with PGR’s 

With this season’s forward crops, growers and agronomists can also simplify and complete agronomy programmes more effectively by tank mixing Axial Pro with Moddus and trace elements, for example. Trials have shown complete wild oat control from tank mixes or sequences with various PGR treatments.

For a complete one-pass solution Axial Pro can also be successfully tank mixed with a range of broad-leaved weed herbicides, including sulfonyl-ureas and ArylexTM containing products. Remember to look at the tank mix list for Axial Pro before applying in mix with any broad-leaved weed herbicides.

Be mindful of weather conditions when tank mixing, especially if there are large swings in diurnal temperatures.

Broad-leaved weed herbicide

However, it is important to note that where Axial Pro is being used in a herbicide sequence that includes SU/ALS or hormone broad-leaved weed treatments, applying the Axial Pro first ensures the grass weeds can be taken out soonest, shortly followed by broad-leaved weeds seven days later. Otherwise, a 21-day interval is required following an ALS/hormone herbicide use, before the Axial Pro can be applied – by which time the grass weeds will be even larger and more difficult to kill, as well as having had a greater effect on yields.

Pete’s tips for grass weed control this spring:
  • Prioritise grass weed timing in the spray schedule
  • Treat fields with larger overwintered weeds first
  • Tank mix with PGRs where required
  • Combine with broad-leaved weed herbicides
  • Adapt application techniques to weed and crop size