Potatoes and wireworm damage

Wireworms, better known as click beetle larvae, feed on potato tubers. Although losses in terms of quantity are low, potato quality suffers significantly as a result of attacks. There are practically no soil insecticides available that are effective against these pests. Only regular soil care helps keep their numbers down to moderate levels (pH > 6). Are there other options to consider apart from the use of insecticides?

Are the potatoes you’ve just harvested full of holes and covered in black spots? Beware, your potato plot may well be infested with wireworm. An increase in these beetle larvae has been observed since the ban on the most radical soil insecticides came into force.

Wireworms, the sly enemy of potatoes!

Wireworms are recognisable by their orange-yellow colour, elongated form and hard shell. They vary in size from 3 to 25 mm, depending on their stage and species. Only the click beetle larvae damage potato crops. Adults are elongated in shape and measure 7 to 8 mm. Most wireworm species (such as Agriotes lineatus, A. obscurus and A. sputator) have a long larval cycle of four years.

In contrast, A. sordidus, the predominant species in the south of France, appears to have a much shorter cycle, either one or two years. The wireworm moves through the soil to feed on the roots of plants, gnawing on and perforating them.

How can wireworm damage be identified?

Wireworm damage to potatoes usually takes the form of a mass of holes and mini-tunnels on the vegetables. How do the wireworms cause so much damage? During the potato planting period, the wireworms are barely active or completely inactive. However, from July and August, they try to escape dry soil. They find the moisture and food required for their growth inside the plants’ daughter tubers. The impact of the holes and perforations are particularly pernicious since they make it difficult to sell the tubers.

How can we deal with wireworm invasions?

Regular soil care remains the best way of controlling wireworm infestation. Wireworms are particularly fond of grass. So if a potato crop has recently been planted over grassland, there will be a higher risk of finding them.

The only chemical solution recommended to control wireworms involves the preventive application of an insecticide. It is also recommended that potatoes not be planted for a period of two years in grass buffer strips returned to production. In fact, the second year is the riskiest, since the larvae primarily eat buried plant matter during the first year.

Another option consists in helping the herbaceous plant to develop a physical and mechanical barrier that may give it greater resistance against environmental attacks.

Wireworms impair the quality of the potatoes harvested and affect yields. If you want to keep your potato crops healthy, look for our products at your nearest “gardening” advice centre.

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Natual is a range of plant-based nutritional supplements designed to support the physiological functions of farm animals and crops, and in particular their natural defences.