How to reduce wireworm tuber damage risk

Wireworm risk should be routinely assessed ahead of potato planting to combat the increased threat of pest damage to crops, say experts.

Historically associated with grassland rotations in south-west England, changing farm practices and climatic conditions have seen a continuous creep of the soil-borne pest to other regions in recent seasons.

Damage from wireworm boring into tubers can result downgraded crops – as well as creating an entry point for tuber rots and disease pathogens, says Syngenta potato technical manager Andy Cunningham.

Any past evidence of infestation indicates the presence of adult click beetle species in the area – and the ongoing threat of its larval stage, wireworm, Mr Cunningham told last month’s Syngenta Potato Power meetings.

Risk factors

Higher pest populations are linked to increases in green cover throughout the rotation, more soil organic matter and moisture retention, reduced cultivations in minimum tillage cereals and fewer insecticidal seed treatments in arable crops.

All these management practices benefit the wider arable rotation, which makes it challenging to employ integrated pest management (IPM) strategies to prevent wireworm damage in potatoes.

Maize grown for forage or energy crop are also a favoured wireworm host. Growers and agronomists should routinely risk assess for click beetle and wireworm populations on fields in advance of potato cropping, says Mr Cunningham.

“Being aware of the problem is key for developing an effective control strategy to target treatments effectively and to minimise damage,” he advises.

Assessment

Monitoring techniques include pheromone traps to attract the three primary click beetle species; and bait traps of seed balls with 50:50 wheat and maize buried in the soil when conditions warm up.

“Pheromone traps are highly selective and give a very good indication of click beetle presence across the area, with capture thresholds as a guide to suggested actions,” says Mr Cunningham.

“Bait traps are more specific to the field, but if you do find any wireworm then it accurately indicates potato crops will be likely subjected to attack.”

The loss of Vydate and Mocap means Nemathorin is now the only nematicide available for growers to reduce wireworm damage, says Mr Cunningham. “Results can be very good, and equal to the nematicides previously used for the purpose.”

When wireworm is the only soil pest to be targeted, the Nemathorin application rate is just 15 kg/ha – half the rate used for the control of potato cyst nematode or for targeting free-living nematodes.

“The application technique is imperative to avoid mixing in too much soil and over diluting the treatment. It needs to be accurately applied and evenly incorporated into the top 15-20 cm of the soil profile only.

“For most growers, that means applying as a specific pass on a bed tiller directly in front of the potato planter,” says Mr Cunningham.

“Nemathorin is such an important and significant investment in the potato growing programme that it makes economic and agronomic sense to get the best performance with accurate application.”

While Nemathorin is the best option currently available, Mr Cunningham suggests that new products under development could offer a better long-term solution to the growing issue of wireworm.

Syngenta trials with an innovative new research product, based on the active ingredient tefluthrin, have shown excellent results, he says. The product formulation gives improved vapour activity in the soil profile around the bait points.

“Application trials have looked at in-furrow treatments to achieve protection around the growing tubers, but for growers who may not have the required applicators overall incorporation has also been successful in the research.”

Results have now been submitted for the product’s UK registration for the control of wireworm in potatoes and maize.

Innovate UK funds wireworm control project

A £56,000 project is assessing new ways to combat the increasing problem of wireworm damage in potatoes. The 18-month Innovate UK initiative is being undertaken by Emerald Research in south-west England. It is evaluating whether soil improvers can deter wireworms by stimulating the reproduction and development of soil microflora.

Wireworm can remain in the soil for up to five years. Losses to the pest are typically 15-35%, says the Agriculture and Horticulture Development Board – threatening crop viability on infested fields.

Fieldscale trials are testing three possible solutions. It is examining the post-treatment level of wireworms in the fields, while also recording the effects on soil health, tuber damage and marketable crop yield.