Can you still make money if you’re trying to reduce blackgrass populations by switching to a spring crop?

What about the effect of introducing cultural control techniques such as ploughing on weed numbers and the bottom line?

These are just two of the questions that Niab Tag’s weed specialist John Cussans is used to hearing as growers consider how they can reduce grassweed infestations with some of the non-chemical options at their disposal.

“We’re at a crossroads. Many growers have good knowledge about different cultural approaches,” he says. “But they are really concerned about the potential impact on margins if they start to make changes, especially now that grain prices have fallen.”

That’s why a computerised planning tool has been developed as part of Artis – a training platform led by Niab that provides technical training for farmers, growers and agronomists – so farmers can work through their rotational information and look at how their gross margins will be affected, both now and in the future.

The tool allows them to see what would happen to blackgrass populations if they made simple changes, by using the starting blackgrass seed bank density within a field and then building in cultural control techniques and herbicide efficacy data.

It also shows how the weed seed bank alters with different approaches – giving an indication of how much cultural control is needed where herbicide efficacy has been lost.

The tool compares the simplistic fixed values for margins that are often used for farm business planning to margins that have been adjusted for the costs imposed by significant blackgrass population levels.

“If you have bad blackgrass, your margins are not the same as those you find in farm management pocketbooks,” points out Mr Cussans.

“And that’s an important place to start. Most of the growers who have made use of the tool are already incurring costs because of the weed.”

That means they may already be operating on margins below £420/ha/year, which is the break-even level on some of the better-performing units, he points out.

“Fixed costs are very specific to individual businesses, but at that level they are going to be close to break-even.

“If that’s the case, their rotations will have to change and simple alterations may be enough.”

For example, a wheat/wheat/oilseed rape rotation coming under pressure from high blackgrass numbers can be adjusted by introducing ploughing in year one, together with slightly later drilling of the first wheat and the use of higher seed rates, he explains.

“There’s a rise in costs from doing this, and a slightly lower yield potential. But the blackgrass population comes under control, and the slide in margins is arrested. So there are fairly instant results from only making changes to the first wheat.”

Taking this example to the next stage, Mr Cussans points out that the information created can then be used for future scenario planning.

“So, if there are no post-emergence herbicide options left that work, you can investigate how much cultural control you need to achieve.”

In this particular situation, by the time years four and five come along, margins are suffering again.

“Herbicide failure means that money is being lost by this stage. Herbicide effectiveness remains a key driver and where control is reduced through seasonal failure of high levels of resistance, there’s much more work to do.”

So what else can be done?

An approach that Mr Cussans describes as “all-in” rescues the situation. By that, he means a combination of very late drilling, introducing a spring wheat, ploughing one year in every three and using high seed rates.

“It puts you back in control,” he says.

Moving from continuous wheat

The effects of rotation are illustrated by one Artis exercise, putting a continuous wheat situation, using non-inversion tillage, though the model.

“In this case, the farm has seen margins fall from £611/ha to £170/ha, so the current situation isn’t sustainable,” Niab Tag’s John Cussans points out.

Introducing winter oilseed rape into years three and six makes a difference, he continues.

“There’s a cost in doing this, so margins drop from £533/ha to £319/ha. It’s better, but not good enough.”

Changing the break crop to winter beans only makes the blackgrass problem worse. “There are gaps in the winter bean crop, so the blackgrass takes full advantage of these. Margins fall to £238/ha.”

Spring beans fare better in that they help to reduce weed numbers. “But the model shows there are still seed return issues,” Mr Cussons says.

However, spring barley does help. “It’s more competitive, so there’s a greater reduction in blackgrass and in seed return. It helps the farm turn the corner.”

But fallowing is the best for blackgrass. “Margins suffer though. It shows that growers with bad blackgrass have tough decisions to make,” he adds.

Final words of advice

“There is no magic solution. Despite the model using the very latest information on the biology of the weed, as well as the effectiveness of herbicides, there isn’t a single strategy or formula,” says Mr Cussons.

“In the end, all the sustainable approaches to weed management have one thing in common – an almost obsessive attention to detail, together with effective integration of herbicide and cultural control approaches.”