Care required for best weed control options

Sugar beet growers looking to rationalise herbicide use should consider the pros and cons of alternatives – which may not suit all situations and seasons.

British Sugar’s in-house weed specialist and technical support manager Pam Chambers has been testing different weed control strategies at a site in Yaxley, Suffolk, for two seasons.

The inspiration for her work is the threat of herbicide withdrawals and the need to reduce reliance on chemistry.

Big losses include the loss of desmedipham in 2020 and recently, the European Union recently banned triflusulfuron-methyl (Debut). Great Britain may soon follow suit soon.

Reasons for the EU’s Debut ban were valid – but its withdrawal document suggests interest in hand or mechanical weeding is making herbicides less important in the eyes of regulators.

‘No standalone solution’

Alternatives may be effective, but Ms Chambers says they may not always be economically viable or as environmentally positive as they appear.

“They all have their place [but there is no one easy, standalone solution for growers, and we need to make this known to both regulators and NGOs to ensure we keep those valuable tools,” she warns.

Going into detail about the Yaxley work, Ms Chambers and her team has been testing a range of weed control options available today, including traditional herbicide spray programmes.

The Conviso Smart system, which was designed to use ALS herbicide tolerant beet to control weed beet and reduce herbicide sprays to just one per season, is also on the treatment list.

Mechanical options include a camera-guided precision inter-row hoe, with or without a band sprayer that applies herbicide on the crop row. The high-tech Ecorobotix 6m hooded spot sprayer completes the line-up.

Weather this year meant crop and weed emergence and growth was variable and led to herbicides being difficult to time, particularly in the Conviso system.

Only one application of the Conviso One (foramsulfuron + thiencarbazone-methyl) herbicide is permitted, timed when trigger weed fat hen reaches four true leaf stage.

This led to some weeds being left behind and means an additional follow up spray will be required and this is a scenario widely reported in commercial crops this year.

“Conviso has its advantages, but in seasons like this you may apply as many sprays as you would in a non-Conviso variety, particularly if you have ALS resistant weeds present. That would significantly increase cost,” says Ms Chambers.

Spot sprayer

Mechanical systems have pros and cons too. Plots treated with the mechanical hoe only has left plenty of Chenopodium species like fat hen within the row this year, which would need to be tidied up with herbicide.

Finger wheel attachments may help improve in-row control, but it’s likely an additional herbicide would be needed to avoid significant yield loss from weeds left behind.

A Lemken tractor hoe and band sprayer combination was added to treatments this year and Pam was impressed with its overall efficacy both between and within the crop rows.

However, such a combination requires significant investment, even with grant funding, and would be most viable where it can be used in other arable or horticultural crops across a rotation.

“Hoes with or without a band sprayer have the potential to reduce reliance on blanket herbicide application, but work rates are relatively slow.

“In a wet year, large growers may struggle to get across their area and weed control is not as good as when its dry, so either system would still require backup,” says Ms Chambers.

Results with the Ecorobotix have been promising so far, but with a price tag of about £130,000, individual sugar beet growers will struggle to justify the investment.

Sharing cost

But growers and contractors are already making it work where high-value crops like onions are in the rotation and there are examples of local groups sharing the upfront cost.

“It uses significantly less water and chemical,” she says.

“But I suspect in fields with a very high weed burden, you would need to apply a pre- or early post-emergence to with a conventional sprayer to reduce numbers before switching to an Ecorobotix.”

Ms Chambers urges growers to really understand the strengths, weaknesses, and economics of each before taking the plunge.