How To Deal With Wireworm in Your Irish Garden
What is Wireworm?
Wireworms are the larvae of click beetles, living in the soil for up to five years before pupating. They are slender, shiny, tough-skinned grubs about 20-25mm long with a distinctive orange-yellow colour and three pairs of small legs near the head. Wireworms are most commonly found in soil that was previously grassland or lawn, as the adult beetles lay their eggs in turf. They are particularly problematic when new vegetable plots or allotments are created by converting grassland. Wireworms feed on the roots, tubers and stems of a wide range of plants underground, causing damage that is often not noticed until plants wilt or harvested crops reveal tunnelling damage.
Damage Caused by Wireworm
Wireworms tunnel into potato tubers, carrots, parsnips and other root vegetables, creating narrow round holes that penetrate deep into the flesh. This makes crops unmarketable and encourages secondary rot organisms to enter. They also attack the roots of lettuce, onions, brassicas and beans, causing plants to wilt and die. Newly sown seeds can be eaten before they germinate. Wireworm damage is worst in the first three to four years after converting grassland to vegetable production. Damage to ornamental bulbs including tulips, gladioli and dahlias can also occur.
How to Prevent Wireworm
When converting grassland to vegetable beds, expect wireworm problems for the first three to four years. Cultivate the soil thoroughly in autumn to expose wireworms to birds and frost. Plant a green manure crop of mustard, which has biofumigant properties that help reduce wireworm populations. Rotate crops so that potatoes and carrots are not grown in the same spot for consecutive years. Trap wireworms by burying cut potato tubers on sticks as bait traps — check every few days and destroy any wireworms found.
How to Treat Wireworm
There are no chemical controls available to amateur gardeners for wireworms. Cultural controls are the main approach: regular cultivation, crop rotation and mustard green manures. Nematode biological controls (Heterorhabditis bacteriophora) show some promise against wireworms but are less effective than for vine weevil. Trap cropping with buried potato pieces helps reduce populations. On allotments and new vegetable plots, accept that some wireworm damage is inevitable in the early years and populations will gradually decline as the soil is regularly cultivated.
Wireworm in Ireland
Wireworms are widespread in Irish soils, particularly in areas with a history of grassland. Ireland's extensive pastoral agriculture means that many gardens, particularly in rural areas, are created from former grassland with established wireworm populations. Allotments and community gardens created on previously grassed sites commonly experience wireworm damage for the first few years. The cool, moist Irish soil conditions allow wireworm larvae to remain active near the surface for longer periods than in drier climates. Organic growers in Ireland rely on crop rotation, green manures and cultivation to manage wireworm populations.
Plants Affected by Wireworm
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