Arable News

  • Written by: Farmers Guide
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Maximising weed control this autumn

As autumn arrives, focus turns to another season of black-grass management. We hear from one farmer who has pushed weed populations down to manageable levels by paying close attention to drilling date and weather conditions.

Ben Stroud, a dairy and arable farmer from Melton Mowbray treats black-grass as the highest priority when planning field operations. By forecasting his drilling dates and crop rotations around black-grass populations and emergence patterns Mr Stroud has seen a notable change in weed burden, thanks to his ruthless approach.

“We prioritise fields on black-grass pressure – we will not even consider drilling anything before 15th October even on clean fields that are free from black-grass, and anything that has even slight black-grass pressure is not drilled until at least the last week of October.”

Land with a high weed pressure is left until spring or used as a grass or lucerne ley which works well alongside Mr Stroud’s 200 head of dairy cattle. Using a traffic light system to pinpoint offending fields, the mapping system is updated each season and decisions are made based on each plot of land with drillings sequenced to target problem areas.

“We are fairly high pressured with black-grass but, on the whole, it has definitely improved in recent years through the system we have put in place. Black-grass control last season was more variable than I’d have hoped – we had some very good success in places we didn’t expect, and then some areas where we hoped we’d get better control didn’t perform as expected. It’s definitely been a season of learning.”

Lessons learnt

Crop rotation also plays a key role in competing with black-grass but reverting back to old systems too quickly has seen control fall short in some areas.

“Where we’ve been hasty going back into a winter cereal rotation we’ve had not such good control, so I think the lesson that’s been learnt is that when you take control measures to improve the black-grass situation you can’t then go back to what you were doing before very quickly.

“The grass and lucerne leys have certainly been beneficial, but spring barley really offers the best level of control because it is much more competitive than spring wheat. We haven’t grown spring beans before, but I feel they’re not competitive enough because you’re seeing a lot of bare soil.”

Farming on very heavy soil makes spring cropping a challenge for Mr Stroud, but he will be increasing his area of spring cropping despite this spring’s challenging weather conditions. 

“Our spring barley didn’t go in until the end of April this year, but it did okay. It wasn’t a record breaker by any means but the fields are very clean of black-grass, so I think drilling later really helped from a weed perspective.

“Something I’ve always held in my mind with black-grass is that if we can’t get a winter cereal in the ground in the right conditions then we’ll leave it and go for a spring cereal.

“It’s much better for us to do that than to try and force a winter cereal into a dry cloddy seedbed that you can’t get a pre-emergence herbicide on in time in good conditions. Black-grass is my number one priority in everything we do here and that includes crop rotation, cultivation, and drilling dates.”

Seed rates

Robust seed rates have also helped to control the level of black-grass, but Mr Stroud says that this should be adapted on a field-by-field basis.

“We increase the seed rate as we go later into October, so we tend to start with quite a robust seed rate anyway because we’re drilling late. We’ll increase that later into October so we’ll probably up it by 50 seeds/m2 in the last week of October and if we end up going into November, a little bit more. 

“With seed rates you have to consider the seedbed conditions and weather as well. When deciding, it’s important to look at what seed rates you’ve used in that field previously and how they fared at harvest and adjust this accordingly, but where we’ve got black-grass pressure the rate certainly needs to be robust.”

Application of a pre-em is recommended within 48 hours of drilling, to allow the active to target the rooting zone of weed.

“We always roll before applying Liberator (flufenacet + diflufenican) but we always get a pre-em on as soon we can. It’s important that you’ve got moisture there and if there is insufficient moisture in the soil, we will hold off with drilling until it is there. We see much better control of pre-ems where the seedbed has got moisture compared to applying to a dry cloddy seedbed.”

Preparing the seedbed as soon as possible after harvest means that black-grass should chit prior to drilling.

“We direct drill with a Claydon drill and we will do a light cultivation in front of that. Last year didn’t quite go to plan with this because it was very wet at the end of August and September. However, we’ve seen the best black-grass control when we do a light cultivation as soon as we can behind the combine and leave it as a stale seedbed right up until drilling. It not only gives the drill a better seedbed and a bit of tilth to work with, but also encourages black-grass to germinate. 

Cultural control

With around 80 per cent of black-grass plants emerging in the autumn, pushing back drilling dates like Mr Stroud is probably the most critical factor in cultural control, according to Prof Stephen Moss who created the ‘5-for-5’ campaign.

“Delayed autumn sowings and an increase in spring cropping is probably the most valuable factor in the 5-for-5 initiative. Not only does it allow black-grass to emerge prior to drillings, but later drillings tend to see pre-ems work better because it’s typically cooler and moister in mid-October than mid-September.

“The key thing is having a five-year plan of action and not thinking you will get on top of this in one year because around 25 per cent of seeds might survive from one year to the next. You can make a lot of progress after five years, but not enough over one or two. You’ve got to look at it long-term to make real inroads.”

And getting over-excited by a drop in weed populations is a dangerous path to go down, according to Dr Moss. “This year people saw good control from pre-ems so black-grass numbers were down, but this could lull them into a false sense of security in thinking they have solved the problem, so they start to drill early again or cut back on herbicides and then they are back to square one next summer.”

  • Written by: Farmers Guide
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