Potato growers were being forced to adopt more post-emergence techniques to control weeds as residual options declined, said experts.

John Keer, from Richard Austin Agriculture, predicted that the succession of dry springs and lack of residual herbicides, with no new products coming onto the market, would force growers to use more post-emergence herbicides to tackle weeds in the future.

Dry conditions meant pre-emergence products were less effective, he said. “Increasingly, with the run of dry springs and a lack of residuals, I think we’re going to be forced down the post-emergence route.”

Dr Keer has been trialling residual and post-emergence techniques for weed control in potatoes.

At the end of May, he planted 30 different varieties at the QV Foods site and has since sprayed them with a combination of different herbicides to see the effects on weed control and plant sensitivity.

Although it is not a full-blown replicated trial, with untreated plots, it has revealed some interesting results, especially when applying metribuzin and bentazone at low rates.

“Once you go down to 0.2kg/ha of metribuzin there are much less levels of damage,” said Dr Keer. “But it’s still enough to kill many different species of weeds which are at the two to four true leaf stage.”

In many cases, he said, there was an appropriate post-emergence herbicide which is safe for the crop.

However, the susceptibility of varieties to various herbicides varied greatly between them, he added.

Maris Piper, Cabaret and Innovator were particularly sensitive to metribuzin, he said.

But Basagran (bentazone), applied at low rates, could be routinely used across a range of varieties with “impressive” results, he added, but there were exceptions.

“Cabaret and Innovator are both hammered by metribuzin, but they look to be very safe to basagran,” he explained.

“However, Desiree, Markies and Russet Burbank are all susceptible to Basagran.”

Another option was to add 0.2kg/ha of metribuzin to Titus (rimsulfuron), which could greatly broaden the weed spectrum to include more common and damaging weeds like polygnums, he said.