A delay in approving the emergency use of neonicotinoid pesticides on winter oilseed rape may result in hikes in the price of the crop next year, experts have warned.

Although Defra this week granted permission to use nicotinoid pesticides, lack of coverage in the weeks directly after the short planting season in late August and early September, had left large swathes of this year’s crop “very vulnerable” to cabbage stem flea beetle, NFU combinable crops adviser James Mills said this week.

Several weeks of evaluation by Defra resulted in farmers last week being given approval to use Insyst pesticide for 120 days from 26 September, and Bayer’s Biscaya all year round.

But up to half of this year’s crop - which is the second most planted in England and represents 15.7% of all UK arable land - had been spoiled to date, said Mills, and the effects could be felt on the global markets at harvest next July. Oilseed rape has applications including biodiesel, cooking oil, animal feed and industrial plastic.

“We operate in a global commodity market which can compensate for some crop losses, but it’s important to remember that neonicotinoids are banned across the EU,” added Mills. “Europe is the largest oilseed rape producer in the world, and if there was a significant infestation of cabbage stem beetle in mainland Europe it could have a big impact on prices.”

The flea beetle had also damaged oilseed rape crops in Sweden and Finland.

It was too soon to see the full extent of the damage in the UK, which would not be fully realised until next year, he said, adding that planting oilseed rape was “all about timing.”

“Not having that neonicotinoid dressing in those first few weeks after planting has had a very real impact,” said Mills.

The percentage of spoiled crops could rise over the coming weeks, warned the NFU.