Why sugar beet growers should re-evaluate herbicide plans

Sugar beet weed control programmes are coming under increasing pressure from herbicide approval updates and rotational changes.

As a result, growers should take time to review current strategies and plan to incorporate a wider range of active ingredients into programmes next year.

That is the view of independent agronomist and Sentinel product manager Martyn Cox, who points out that a number of key products are being limited, lost or under threat from withdrawal.

Pre-emergence loss

Cost effective pre-emergence herbicide chloridazon is a useful option for holding back early weeds, taking pressure off later applications and potentially allowing growers to cut out a post-emergence spray or use lower rates.

See also: The secret to Norfolk farm’s record-breaking sugar beet yield

However, the active is being withdrawn next spring and, combined with the removal of lenacil-containing Venzar’s pre-emergence recommendation, it means there are just two pre-emergence actives available.

These include ethofumesate, but with a rotational limit of 1kg/ha over a three-year period, its use will have to be carefully planned to avoid exceedances.

This is particularly true where sugar beet is being grown on heavier land to manage blackgrass and the active is likely to be applied to other crops in the rotation, such as wheat.

Lower rates

The second pre-emergence option for sugar beet growers is metamitron, but products containing the active have also experienced restrictions in recent seasons.

Goltix Flowable – which had a maximum individual dose of 3 litres/ha and a maximum total dose of 15 litres/ha – has been replaced with Goltix 70 SC, a product with a lower individual dose of 2 litres/ha and a significantly reduced total dose of 5 litres/ha.

“If you put 2 litres/ha on as a pre-emergence application, it doesn’t leave growers much to play with for post-emergence residual top-ups,” explains Mr Cox.

He adds that Goltix helps control acetolactate synthase (ALS)-resistant oilseed rape volunteers where Clearfield varieties are being grown, so being able to use less herbicide might see growers run into issues with this tough-to control weed.

“[ALS-inhibitor] Debut [thifensulfuron-methyl] will struggle, so we are starting to see these restrictions and rotational issues making sugar beet weed control more complex. It is like creeping shellfire – there is a slow erosion of options and more pressure is placed on what we have left,” explains Mr Cox.

Sugar beet herbicides key points

  • Loss and restrictions of key pre-emergence products
  • Limits on post-emergence residual top-up options
  • Threat to future of phenmedipham and desmedipham
  • Growers should evaluate current herbicide programmes and alternative products ahead of 2020

Residual options

In addition to Venzar (lenacil) having a pre-emergence recommendation removed from the label, its maximum individual and total doses have dropped from 5 litres/ha and 6.3 litres/ha to 0.4 litres/ha and 1 litre/ha, respectively.

The active has also been limited to a maximum limit of 500g/ha over three years to the same field.

Mr Cox says this further reduces post-emergence residual top-up capability, and with uncertainty over the future of phenmedipham and desmedipham – which underpin weed control programmes in sugar beet – it is wise to establish how alternatives fared this spring.

These include dimethenamid-P and quinmerac co-formulations such as Butisan Pro, Tanaris and Topkat, which were recently added to the sugar beet herbicide portfolio.

They are used at early post-emergence and are strong on weeds such as cleavers, dead nettles and fool’s parsley.

Herbicide tolerance

ALS herbicide-tolerant sugar beet varieties from KWS also have the potential to help in weedy situations when available next season, but Mr Cox says this needs to be carefully managed to avoid putting undue pressure on one chemical group.

“We already have ALS resistance in grassweeds such as blackgrass and ryegrass, and broad-leaved weeds such as poppy, so it will need to be backed up with alternative modes of action,” he says.

Sentinel tool

Sentinel is a decision-support tool linked to Gatekeeper crop management software, a program that helps arable farmers with record-keeping and legislation issues.

For more details visit the Farmplan website or call 01594 545 011.