Growers deploy nematodes to defeat vine weevil

16/04/2020 - With the EU ban on thiacloprid products such as Exemptor, Biscaya, Calypso, growers are increasingly turning to beneficial nematode control in their fight against black vine weevil (Otiorhynchus sulcatus). 

Uniquely offering both contact and systemic action, many growers were heavily reliant on thiacloprid to provide protection from this challenging pest of soft fruit and potted ornamental crops. However, entomopathogenic beneficial nematodes offer a welcome, effective biological alternative when applied at the correct time and with a programmed approach. 

Timing is important

Check potted plants regularly for the white, C-shaped larvae that feed on roots over winter and in to spring, weakening or even killing plants. After a pupation period of 1-2 weeks, the adults emerge and feed on the above-ground parts of the plant, causing characteristic ‘notched’ leaf edges. 

Now is the ideal time to develop a new strategy for controlling vine weevil with regular applications of nematodes

Emerging adults may start laying eggs as early as April; therefore, to ensure year-round control apply nematode treatments monthly from June to October via drip irrigation. In cooler spring conditions, choose the Kraussei-System; later, once temperatures are consistently above 12°C switch to B-Green. Nematodes work best in well-watered medium, so drench applications may be applicable in some situations.

Scheme Vine weevil

The scheme shows when various stages of the vine weevil lifecycle are present over the months of the year. The number of coloured bars indicates the likely population level (for each stage of the pest's lifecycle), with three bars depicting peak populations. So eggs are likely to peak in August, larvae in September and October, pupae in May and adult vine weevils in June and July. Taking in to account this information, as well as likely growing media temperatures, the scheme recommends timings for applying Kraussei-System and B-Green beneficial nematode controls.

Photo by Denny Bruck

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