Unpopular guest in potatoes: wireworms

Background and Objective

Is it possible to reduce the damage by wireworms and thus to ensure the quality of organically produced potatoes? This was the aim of the project partners under the coordination of the Landwirtschaftskammer Nordrhein-Westfalen, in cooperation with the Thünen-Institute of Organic Farming, the Kompetenzzentrum Ökolandbau Niedersachsen (KÖN), the Landesbetrieb Landwirtschaft Hessen (LLH) and Dienstleistungszentrum Ländlicher Raum (DLR) – Rheinhessen – Nahe – Hunsrück.

Approach

First, we set up pheromone traps on farms to catch the adult click beetles and reduce the population permanently. We conducted a monitoring of the larvae in the soil for damage prediction. In addition, we examined specific soil tillage methods for reducing wireworms. We wanted to derive transferable strategies for practice from the results.

Results

The results show that red clover-ryegrass-mixtures are highly attractive for click beetles. This supports the assumption that a high proportion of clover-grass in the crop rotation favors the population of wireworms. In organic farming, clover-grass is essential for fodder production, N₂-fixation and humus formation, but in potato production clover-grass increases the risk of an infestation with wireworms. During the entire course of the project it was not possible to correlate the number of trapped click beetles and/or the number of collected larvae to the damage they caused on the harvested potatoes. Apparently other factors, such as soil parameters, climate conditions but also biotic factors (e.g., such as predators, nematodes, fungi) must be taken into account. Since wireworms need up to 6 years to develop, long observation periods are needed. No pesticides are available in Organic Farming for direct control – therefore the wireworm population must be reduced by agronomic practices. The effect (bio-fumigation) of different preceding crops (e.g., white cabbage) and soil tillage at the right time could reduce wireworm damage to potatoes.

If pod-solid potatoes are harvested early, the damage caused by wireworms can be reduced considerably. A long residence time in the soil increases the extent of wireworm damage. No, or a hardly reducing, effect on the infestation with wireworms was found after the cultivation of cover crops, undersown crops, the use of different composts and soil additives, or a treatment with plant strengtheners.

It is assumed that only systematic long-standing action can permanently reduce the damage caused by wireworms. For this suitable long-term experiments are required.