Brian Fitzwater of Fox Galcier asks :-

In five years as a resident at Fox Glacier I have not been able to grow pototaoes owing to the presence of what the locals call wireworm. The worms are thin, redish to dark brown and about 10-15 mm in length. When dug up the potatoes are riddled with tunnels and usually the worms are still resident. What are they and can I get rid of them?

Nicholas Martin, an entomologist with Plant and Food Research in Auckland, responded.

Wireworm are the root feeding larval stage of click beetles. They can live in the soil for two or more years before becoming adults. They are recognized by their distinctive rear end. Usually they are a problem when growing a crop in ground that was previously in grass. It is very difficult to treat the soil to control them as the larvae can live deep in the soil and later come to the upper layers and burrow into potato tubers.

The best bet is to grow another crop, that is not harmed by wireworm, for a season before growing potatoes in the same soil.