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Agroscope, University of Fribourg

Biocontrol of Wireworms in Cover Crops

Crop Protection 150, 105811, 2021

Wireworms cause significant crop losses in potatoes. This study investigated the efficacy of a fungus in decimating wireworm populations in the winter cover crop. The strategy was partially successful, but must be further optimised for use in practice.

Wireworms – the soil-dwelling larvae of the click beetle – can cause significant crop losses in potatoes by creating holes in the tubers. Ideally, measures for controlling wireworms should be effective but also environmentally and user-friendly. The lack of such efficient control measures necessitates a search for new options.

Entomopathogenic fungus as an antagonist

One possibility is the use of fungi that occur naturally in the soil and attack insects, such as Metarhizium brunneum. This study tested a method for the preventive control of wireworms in winter cover crops and compared it with currently authorised synthetic insecticides.

The method of application was adapted to the biology of both the fungus and the wireworm. Because wireworm development takes several years in the soil, the treatment does not necessarily need to take place during the potato season, but can be done preemptively. When applied together with the sowing of the winter cover crop in late summer, the fungus finds better infection conditions at high soil temperatures. Plant cover and the winter fallow period protect it from environmental influences, thus extending the duration of effect.

Higher wireworm mortality, but insufficient reduction of potato damage

The fungus was found in elevated concentrations in the treated soils, and remained vital over eight months until potato cultivation. The treated soils sharply increased wireworm mortality in laboratory tests, and the applied fungus was recovered from individual specimens collected in the field. However, a statistically significant reduction in potato damage was only found in two out of ten trial fields.

Treatments with the synthetic pesticides were not more successful, as they also failed to reduce wireworm damage sufficiently.

Application in the cover crop proved favourable for boosting numbers of the wireworm antagonist M. brunneum in the soil. For reliable use in practice, the plant-protection strategy must be further improved.

Conclusions

  • The application of the fungus Metarhizium brunneum, a natural antagonist of wireworms,strongly increased the presence of the fungus in the soil over a period of several months as well as affecting wireworm survival rate.
  • Neither the biocontrol method nor use of the authorised synthetic pesticides led to satisfactory damage limitation.
  • The factors limiting the success of wireworm control are not yet sufficiently researched. Our study underscores the importance and urgency of further investigations in order to provide efficient protection from wireworm damage.

Scientific article

Biocontrol of Wireworms in Cover Crops

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