The problems caused by winter stem weevil in oilseed rape crops this year may have been unintentionally caused by bringing drilling dates forward.

The adults have an earlier egg-laying period than that of cabbage stem flea beetle, so efforts to avoid one pest might have played into the hands of another, suggested some agronomists at Cereals 2023.

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Not spraying pyrethroids or using insecticidal seed treatments for flea beetle and turnip yellows virus-carrying aphids could also be behind the pest’s resurgence, with particular problems seen in East Anglia this year.

Recognisable by their distinctive C-shape and dark orange head, the larvae are often found living alongside flea beetle larvae in the plant in the spring, where they invade the main stem and developing crown.

Colin Peters, oilseeds specialist at Niab, stressed that there is a lack of information on stem weevil and its life cycle, but added that current monitoring work being done on cabbage stem flea beetle pupae will include stem weevil if it is present.

“We will record them if we find any,” he said. “We are doing weekly soil testing until October and will hatch and identify pupae. It may be that winter stem weevil has a fit with flea beetle – we just don’t know.”

His work on flea beetle is aimed at finding the point in its life cycle where it is vulnerable and damage can be inflicted.

“Based on very limited information from last year, that could be while they are still in the soil as pupae, before they hatch and migrate into the new crop.”