Review of herbicide ‘risk assessment’ is needed

Future pesticide approval reviews should include an assessment on what was in the entire portfolio of products for particular targets rather than be solely on an individual product basis, James Clarke, an ADAS weed scientist, suggested to delegates at Bayer CropScience’s Weed Focus conference.

Reviewing the long term prospects for combinable crop weed control he noted that most current products were under threat from either resistance or because of potential issues with water quality.

Already isoproturon and trifluralin had failed to be re-registered for approval at either the UK or EU level because of water quality concerns, he pointed out. And other products could go the same way. “Personally I think if you asked the same questions of chlorotoluron [as were of IPU] you are likely to get a similar outcome.”

Oilseed rape residual herbicides propyzamide (as in Kerb) and carbetamide (as in Crawler) were also now found in water and under scrutiny. “We’re using more of them, so for that reason alone, we’re likely to find them more in water. The higher use area overcomes many of the properties of the product.”

Most other active ingredients, including sulfonylureas, and fops and dims, and residual herbicides, such as pendimethalin, were threatened by enhanced metabolism and/or target site resistance.

It left products in danger of being picked off one-by-one, he said.

Changing the regulatory system from one based solely on individual product approvals to one including an assessment based on portfolios could help maintain at least some choices, he suggested. “We need a strategic assessment across a portfolio.”

Don’t let politics get in the way

  • The loss of IPU was more to do with politics than science, Guy Smith, Essex farmer and conference chairman, said.

  • By leaving monitoring of pesticides in water to the utility companies farming had left itself open to their loss, he suggested. “The industry must monitor for itself and not being dependent on others to do it for us.”

That would allow products to be compared, he explained. “Who knows, if IPU or trifluralin were assessed within a portfolio, they might turn out to be of least concern – we just don’t know.”

Localised risk assessments should also be considered, for resistance, biodiversity and water quality, he said. “If we assess everything on the worst-case basis, they may all fail, while a local risk assessment might allow some use in specific situations.”

Three x three equals success

Three is the magic number to remember when it comes to chemical blackgrass weed control this season, Patrick Stephenson, an independent agronomist from North Yorkshire, said.

“Apply a product within three weeks of drilling, apply at least three different modes of action, and your post-emergence spray needs to be on by the three-leaf stage of the weed,” he explained.

Encouraging growers to stop drilling to put on a pre-emergence spray was a challenge, he noted. “Growers want to be drilled up because of the weather believing we still have chemistry to control blackgrass.”

But the herbicide armoury was dwindling with loss of IPU and trifluralin and increasing resistance, he stressed, and there wasn’t anything new in the pipeline. “We picked ‘hope’ out of Pandora’s box five years ago [when Atlantis was launched]. Now the box is empty.”

Post-emergence sprays had to be on by the three-leaf stage of the weed, preferably in the autumn, he advised. “If you wait until the beginning of November, in all honesty, that probably means March. I would rather have the product on and working than wait for March.”

The lack of chemical options would likely force growers to return to the plough, he predicted. “Leeds has a band called the Kaiser Chiefs*, who have a line in one of their songs, ‘What’s that coming over the hill, is it a monster’. Well, farmers will be saying ‘what’s that coming out of the bushes’ and it will be this thing [the plough],” he said.

“The plough will have to return, particularly if you want to drill in August or September.”

* The song is actually by The Automatic – Editor