Q: Last year I lost a lot of young seedlings and transplants in my new allotment to wireworm damage. My main crop of potatoes was also damaged. Is there any way to stop this happening again without using chemicals? I garden organically, and don’t want to use insecticides.
Sarah Byrne, Dublin
A: Bright orange-brown in colour and about 2.5cm long, wireworms are the soil-dwelling larvae of the click beetle and can cause a surprising amount of damage to the root systems and stems of both seedlings and mature plants. Along with young seedlings, favourites include root vegetables such as potatoes, carrots and beetroots, but they will also tunnel into the fleshy root systems of ornamental bulbous plants such as dahlias and anemones. Not only is this damaging in itself, it also leaves them vulnerable to decay and subsequent damage from slugs.
The adult female beetles lay their eggs in the soil from very early summer, with successive generations hatching out over the following months and then hungrily searching for food. While the larvae are active throughout the year, damage is typically at its worst in spring and then again in autumn, when the soil is warm and moist without being too hot or too cold. It can take up to five years for them to pupate, during which time they remain in the soil.
Wireworm damage is much worse in freshly cultivated soil, especially if it was previously under grass. If this was the case with your new allotment, be reassured that the damage will decrease over time, with regular cultivation of the soil disrupting this pest’s life cycle along with wireworm’s natural predators, which include birds, frogs, hedgehogs and other kinds of beetles. Finally, careful crop rotation is important for the same reason.
To help the process along, try using mustard as a quick-growing green manure on any empty beds. This acts as a natural biofumigant via its roots, which release gases poisonous to wireworms.
Another option is biological pest control, which uses specific kinds of naturally occurring microscopic nematodes (Steinernema) in a targeted way. Approved for organic food production and available from mrmiddleton.com and fruithillfarm.com, these kinds of live products need to be ordered in advance and are effective only when environmental conditions are suitable, requiring an overcast day, a damp, warmish soil and air temperatures between 5C-20C.
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