While delayed drilling and spring cropping have become mainstays for many in the fight against grassweeds, especially black-grass, the use of crop competition is perhaps an underrated component of a successful integrated weed management programme.
More vigorous varieties or higher seed rates of wheat can play a part in increasing crop competition, but the most effective grassweed competition will be through growing winter barley, and especially hybrid barley.
Potentially it can be better than a spring crop, suggests Georgina Young, a Syngenta field technical manager.
“In a trial comparing spring barley, conventional winter barley and hybrid barley, the grassweed control was reduced in the spring barley because it established poorly and the lack of competition increased weed problems.
“There is definitely a case for a good competitive autumn crop being a good choice, even versus spring cropping when you can’t guarantee what the spring
conditions will be.”
The grassweed suppression comes from both above and below ground effects, says Ben Urquhart, seed technical expert for Syngenta.
“Hybrid barley is a very competitive crop – it provides fantastic competition above ground through aggressive spring growth. It produces lots of tillers which we can support with an early dose of nitrogen.
“The story also continues underground through a big root system, which ADAS research has shown is significantly larger across a number of different measurements than in a conventional variety. That helps the crop compete with grassweeds for nutrients and water, but also helps with anchorage for the vigorous canopy.”
While hybrid barley’s suppression of black-grass is well-known – in Syngenta trials it offered around 80% more suppression of black-grass heads/sq.m than a conventional six-row variety regardless of hybrid barley variety, the same also applies with other grassweeds, including ryegrass and brome species, Mr Urquhart says.
“The agchem toolkit is not as good as it was for ryegrass, so it is becoming more problematic. But what we have seen with black-grass holds true for ryegrass and bromes.
“Hybrid barley is significantly better than conventional six-row winter barley for suppression, which in turn is better than tworow barley, with wheat providing the least competition.”
That improvement manifests in reduced grassweed tiller numbers and usually also a smaller weed, resulting in lower seed return.
In Syngenta ryegrass trials there were around 50% fewer ryegrass heads in hybrid barley than in two-row barley and 65% fewer than in wheat. A bigger proportion of those heads were below the crop, which typically produce lower numbers of seeds.
The same trends were seen in a joint Syngenta/Agrii brome trial near Edinburgh, with fewer plants producing fewer tillers and seeds per plant, plus a delay in brome seed maturity where hybrid barley was grown.
Maximising grassweed control with crop protection in the hybrid crop is also crucial to take advantage of its competitiveness, adds Mrs Young.
“Thinking about drilling when you know you have opportunities for applying a pre-emergence following drilling in a reasonable time scale is crucial.
“There is no point drilling a competitive crop if you know you will not be able to get the pre-em on.”
Pre-emergence sprays are the foundation of the herbicide strategy in hybrid barley, as in wheat, because of the increasing resistance to post-emergence options, she says.
“In the worst affected areas stack different strategies together.”
That includes delaying drilling, if possible, and then applying the pre-emergence within 48 hours of drilling.
“Flufenacet, diflufenican and Defy work best as the base of a herbicide stack and then topping up two to three weeks later, in a black-grass situation, with additional flufenacet,” she says.
“We consistently see Defy adding to the control from the likes of Liberator and Crystal.”
Using hybrid barley in combination with these types of programmes improves the overall impact, Mrs Young points out. In a trial that stacked various
control measures, growing hybrid barley at the recommended seed rate for grassweed suppression of 250 seeds/sq.m with no other control measures gave a 5% improvement over conventional barley or wheat in black-grass control.
“When you stack other factors on top, we saw the difference between conventional and hybrid grassweed suppression increase. For example, if you also use a
pre-emergence then the benefit of the hybrid barley increased to 18%.
“By reducing the number of grassweeds by using pre-emergence chemistry, you’re giving the hybrid barley less of a population for its suppression to act upon, so it is more successful in doing so.”
Where the pre-emergence programme of Liberator (flufenacet + diflufenican) plus Defy (prosulfocarb) was followed up with a peri-emergence residual herbicide and then Axial Pro (pinoxaden) it was possible in this trial to reach 98% control in the hybrid barley crop.
“If you get all the other factors right, including cultivation strategies, it is possible for hybrid barley to be a cleaning crop for grassweeds,” Mrs Young says.
MAXIMISING grassweed control in hybrid barley:
- Drill mid-October to allow stale seedbed before drilling
- Seed rate of 250 seeds/sq.m
- Pre-emergence stack including Defy and flufenacet
- Top up with additional flufenacet
- Apply between 30-50% of nitrogen from mid- to late February to increase tiller retention and promote early spring growth
- Consider spring post-em Axial Pro where necessary
DIGITAL TOOLS COULD HELP IMPROVE WEED CONTROL
FROM weed mapping to variable seed rates and green on brown or green spray applications, digital technology is starting to play a role in improving the decision-making and efficacy of weed control in-field, says Sam Grimsdell, Syngenta digital agriculture manager for the UK.
At the basic level, weed mapping is a very simple way to understand where weeds are in the field and population levels.
“There are various scouting apps available or entering it into your farm management software can give you data insight.”
Syngenta’s Protector app is one such tool.
“It is an advanced scouting tool, which allows you to drop a pin and quantify what weed population, for example, is there.”
Currently that is a manual count, although Syngenta is researching whether it could be done automatically on the phone in the field, offline.
Satellite or drone imagery can also help with identifying where and at what density weeds are in fields too, although it does need some ground-truthing.
Those maps can then be used as the basis for variable rate applications, whether it is seed rates when drilling or herbicide applications, for which the technology is becoming available.
Variable rate drilling could allow growers to increase seed rates in areas where there are higher weed populations to take advantage of the competitive nature of hybrid barley, for example, while maintaining a lower optimum seed rate in other parts of the field, Mr Grimsdell adds.
Mapping could also drive where to make herbicide applications.
“It is more on-off currently rather than upping the rate of product, so avoiding broadacre application.
“But as hardware for on-sprayer detection improves detecting what is there in the field in real-time, green-on-brown and even green-on-green spraying is developing.
“There are farmers using this, although there are some challenges in the UK because of the density of our canopies, especially for the greenon-green systems.”
Decision support systems are also emerging to help predict germination timings, which could finesse application timings. Other models help growers understand the impact of weed control strategies on the evolution of resistance.
“Fundamentally it is about informing farmers with multiple sources of data to fit into an integrated strategy. There is still a lot of work to be done to make these
systems more accessible and easy to use, but integration with other farming systems is improving.”