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Wild oat priority for spring barley competition

Agronomy Issues
06.04.2020
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Spring barley early emergence

Over recent years pre-emergence herbicides have been the mainstay of annual meadow grass and broadleaved weed control for spring barley in Scotland, with an estimated 70% of the area typically being treated each year, compared to less than 40% of spring barley nationally.

However, the benefit of pre-emergence treatments has historically been limited for later drilled spring crops and in dry conditions - both of which could be the situation this season. That means growers will be more likely to look at post-emergence herbicide options, which could have implications for timing and sequencing, according to Syngenta Technical Manager, Georgina Wood. 

Georgina Wood

“SRUC has highlighted wild oats are the most competitive weed in spring barley crops,” she said. “Which makes it a priority for herbicide programmes. Cleavers and black-grass, which are highly competitive in winter wheat, appear to have far less impact in spring barley, but may still be targeted for rotational control.”

Winter wild oat on left vs common spring wild oat

Whilst spring seedbed preparations should knock-out over wintered and early germinating wild oats, they can still emerge over a protracted period in the spring, she warned.

“Understanding the different wild oat species present on your farm, and the effects on germination and emergence, is useful in deciding a control strategy and the most appropriate treatment timing,” Georgina advised.

See how to ID different wild oat species and implications for your herbicide strategy

 Pictured above, with winter wild oat seed (left) typically having two tails, compared to one tail with spring or common wild oat

For treatment of small wild oats, less than GS29, applications of Axial Pro can be as low as 0.4 l/ha. However at low rates the application conditions must be ideal and with weeds actively growing. At the lowest rate it also requires the addition of Adigor, or similar MSO adjuvant, at 0.5% of spray volume. She also cautioned that stress of dry conditions on the weed could compromise efficacy.

In most instances, an application rate of 0.6 l/ha would be the preferred option and, with the new Axial Pro formulation requires no additional adjuvant. That is also the lowest dose for tank mixing with SU or halauxifen-methyl herbicides.

Targeting grass weeds early before the canopy closes in

Georgina pointed out there are some other important considerations with sequencing herbicide applications, specifically to wait seven days before applying an SU/hormone following Axial Pro.

“Furthermore, if you have applied an early SU/hormone herbicide, you will need to wait 21 days before applying Axial Pro – which needs to be taken into account for any herbicide programme.” She also added not to use Axial Pro in mixture with hormone-containing herbicides.

To help with sequence gaps, growers can still take out weeds such as cleavers, cranesbill and fumitory when they are quite large with halauxifen-methyl herbicides, and there is greater flexibility for that on weather condition timing.

Spring herbicide application advice

To achieve the most effective spring post-emergence herbicide results, Syngenta application specialist, Scott Cockburn, advocated early treatments, when weeds and crop are similar size, should ideally be made using angled 3D Nozzles, alternating forward and backward along the spray boom to give good coverage of exposed weeds.

Scott Cockburn

However, as the season progresses and crop gets taller, the preferred option would be to move to an Amistar Nozzle with coarser droplets. That will penetrate the canopy better and get coverage onto sheltered weeds.

“With finer nozzles, such as the 3D, there can be the temptation to up pressure in thicker crops in an effort to push the spray through to the weeds,” he advised.

“But in fact that can be counterproductive, as it creates more small droplets that are better captured by the crop leaves, or worse still lost as drift.”

See the Syngenta Spray Dudes explain the principles of spring herbicide application

If growers do make a pre-emergence application onto spring barley ground, Scott urged sprayer operators to follow the mantra of Go Low; Go Slow; Get covered.

90% drift reduction nozzles for pre emergence application

“The aim should always be to maintain the boom at 50 cm above the target, spray at less than 12 km/hr - which will also help boom stability – and use a water volume of 200 l/ha, with a nozzle selected to deliver that at 2 to 2.5 bar,” he added.