A well-known herbicide, widely used on oilseed rape, has been re-registered – just in time for this season’s applications.

When approval for Kerb Flo (propyzamide) expired last spring, many agronomists and growers thought it would no longer be available, says Dow Agrosciences’ Colin Bowers.

But that was never the intention, adds Mr Bowers, and the firm has spent £400,000 ensuring that the product, which has been on the market for about 40 years, may continue to be used.

With no known blackgrass resistance to the chemical, it is seen as a valuable weapon in the war against that particular weed.

Re-registration comes after water companies detected more propyzamide in water than was permitted under EU legislation, he notes.

“In the past two years, it’s been found at levels causing concern – up to 0.3-0.4ppb at peak times.” The EU limit for any single pesticide in drinking water is 0.1ppb.

As long as farmers take care not to allow propyzamide to get into water by following VI recommendations, Mr Bowers expects the new temporary registration to be extended to a full 10 years.

A key point, bearing in mind that Kerb works best when soils are cold and moist, is to avoid application to soils above field capacity, he says. Spraying onto saturated land risks surface run-off.

“There’s a difference between damp and soggy. We’ve done a lot of work with water companies. The trigger for treatment is about 80% field capacity, and you shouldn’t spray beyond field capacity.”

Propyzamide is not the only oilseed rape herbicide under scrutiny by water companies. Carbetamide, metazachlor and clopyralid are all being examined, says ProCam’s David Ellerton.

“If we lost them, it could be disastrous. The problem with propyzamide is that everyone tends to apply it at the same time. And because we’ve had some dodgy rape seed-beds this year, a lot of the Butisan-type products haven’t gone on. So there could be even more Kerb used this year.”