Leaving aside any possible shrinkage in the herbicide armoury from the latest EU pesticide proposals, weed control in potatoes will become trickier and more expensive after the withdrawal of paraquat and the likely lower permitted linuron dose, Potatoes in Practice plots suggested.

To highlight the need for mixtures Agrovista’s demonstration, on the site where fumitory was a particular challenge, compared results from a range of residual and contact products used alone.

“Linuron at 1.25 litres/ha on its own simply won’t cut the mustard,” said the firm’s Andy Steven. Mixtures would be essential to ensure a good spectrum of weed control, he explained.

“We’re going to have to move away from single products. I’ve been using a lot of four-way mixtures this year and the results have been good.”

One clear message was that paraquat substitute Shark (carfentrazone-ethyl) needed applying pre-crop emergence to avoid checking potato growth.

Andy Steven

Andy Steven found no single product controlled fumitory on the SCRI site

The SAC demonstration of various mixtures, where in places the fumitory was so rampant in untreated plots that it had to be removed by hand to avoid interfering with the treated ones, highlighted the importance of adequate moisture for good results from residuals.

The dry May meant Defy (prosulfocarb) mixtures had worked best when applied at 10% crop emergence by which time some rain had fallen, noted Mark Ballingall. And only under low weed pressure should doses below 4 litres/ha be contemplated, he suggested.

Basta (glufosinate-ammonium) had to be applied pre-crop emergence, he warned. “It needs sunlight to work well, but it has a very good weed spectrum.”

Artist (flufenacet + metribuzin) was generally “under-rated”, he believed.

Both men reckoned growers should budget for weed control to be 10-20% more expensive than last season given the absence of paraquat and the likely linuron restriction.

Commenting on the latest EU proposals Mr Steven said: “If we lost all these products we’d be back to mechanical weed control.”