Project description

The sustainable regulation of wireworm populations is becoming increasingly important. Rising average temperatures, more frequent dry periods and the increasingly limited availability of soil-active insecticides in the entire crop rotation are directly linked to increasing pest pressure from wireworms.

As part of the "Wireworm Control" project, various control measures against the wireworm are being evaluated. One promising approach to wireworm control is the optimisation of tillage intensity and tillage timing, taking into account the activity phases of click beetles. The effectiveness of this measure is being evaluated as part of a comprehensive and practical study design. To this end, one-year and multi-year trials will be carried out in various regions within the usual regional crop rotations in potato and maize cultivation. Furthermore, trials with insect-pathogenic fungi, attractant strips, press residues and insecticides will also be carried out. As part of the project, trials are also carried out in the greenhouse and in the laboratory. Here, under controlled conditions, more detailed knowledge is gained about the preferred oviposition sites of female click beetles, the carrier material of insect-pathogenic fungi is optimised and the influence of fertilisers and soil additives on the vitality and development of wireworms is investigated. In the project, wireworms are also collected and determined directly after the potato harvest and from damaged maize plants in order to systematically record the relevant pest species in the regions and develop targeted control measures.

In the final year of the project, the publication of a catalogue of recommendations to support farmers and agricultural advisors is planned based on the project results.

Preliminary results

• As the available plant protection products are not sufficient on their own to reduce the economic damage caused by wireworms to an acceptable level in the event of a severe infestation, a site-specific, multi-year package of measures is required. Only the implementation of several well-coordinated measures across the entire crop rotation offers the potential to reduce wireworm populations in the field and limit economic damage.
• Multiple instances of shallow tillage between the cereal harvest and the establishment of winter cover crops, or alternatively in the spring, for example as part of mechanical weed control, led to a reduction in the wireworm population in our trials (predominant wireworm species at the trial sites: Agriotes ustulatus, A. sputator and A. brevis).
• In the case of late planting (late August, early September), winter cover crops had no effect on the wireworm population (predominant wireworm species at the trial site: A. ustulatus).
• In the case of preceding crops with a later sowing date (e.g. millet), lower wireworm numbers were recorded in the following year than for preceding crops with an earlier sowing date (e.g. emmer) (predominant wireworm species at the trial site: A. sputator and A. brevis).
• Tests to date with various fertilisers and soil additives, including humic substances, plant extracts and calcium cyanamide, showed no measurable effect on wireworm vitality compared to the untreated control. This was established in laboratory trials using single and tenfold application rates over a five-week trial period.
• The use of trap crops in combination with insect-pathogenic fungi can reduce the population of wireworms in potatoes and maize. The greatest challenges currently lie in choosing the planting time for the trap crops, in the cultivation technique, and in weeding and mulching the trap crops.
• In the field trials, entomopathogenic fungi (Metarhizium brunneum) achieved an average efficacy of 10% when rainfall was sufficient.
• In a multi-year field trial, the addition of water-retaining hydrogel did not result in improved efficacy of insect-pathogenic fungi (M. brunneum).
• The addition of chitosan to the culture medium leads to an improvement in the germination and spore formation of insect-pathogenic fungi (M. brunneum).
• Clover and wheat are particularly attractive to female click beetles (A. sputator) (laboratory results from an olfactometer).

Benefits of the project

The resilience of wireworms and their perennial development require site-specific, multi-year strategies in which several measures must be combined in order to effectively reduce the wireworm population. As part of the "Wireworm Control" project, available control measures are being evaluated in terms of their effectiveness and sustainability. In addition, new measures against the wireworm are being developed in close cooperation with practitioners. The results of the practical trials will ultimately be incorporated into the development of recommendations for action. The catalogue of recommendations will include the measures tested in the project as well as an assessment of their effectiveness, sustainability and practicability.