Wireworm damage is now an increasing risk in potato crops across the country, including eastern counties and up into the Scottish Borders. 

This highlights the need to understand the reasons behind its spread and how to manage it.

Historically associated with grassland rotations in the South and West, changing farming practices and climatic conditions have seen a continuous creep of the soil-borne pest over recent seasons, reports Andy Cunningham, Syngenta potato technical manager.

See also: 6 steps for granular potato nematicide best practice

Damage from wireworm boring into tubers can result in high levels of crop downgrade, as well as creating an entry point for tuber rots and disease pathogens.

Any historic evidence of infestation indicates presence of adult click beetle species in the area – and the ongoing threat of its larval stage, wireworm.

Andy warns that higher populations of the pest have been associated with increases in green cover throughout the rotation, increasing organic matter and soil moisture retention, reduced soil cultivations in min-till cereal establishment and less use of insecticidal seed treatments in arable crops.

Maize, for forage or energy crop, is also a favoured host for wireworm.

Wireworm threat is increasing due to a number of reasons:

• Favourable climatic conditions
• More host cover crops
• Reduced rotational cultivations
• Improving organic matter
• Grassweeds in arable crops
• Fewer insecticidal seed treatments.

Risk assessments

Andy highlights all these risk factors for wireworm damage in potatoes are beneficial for the arable rotation. 

This makes for challenging integrated pest management strategies through the rotation.

He urges growers and agronomists should now be routinely risk assessing for click beetle and wireworm populations on fields in advance of potato cropping.

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

Monitoring techniques can use pheromone traps, with lures specifically for the three primary Agrostis (click beetle) species.

Using bait traps of seed balls with 50:50 wheat and maize buried in the soil can also work when conditions warm up, where wireworm are attracted to carbon dioxide produced as the seeds germinate.

“The 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.

“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.”

Chemical control

He points out that with the historic loss of Vydate and Mocap for wireworm control, Nemathorin (fosthiazate) is now the only nematicide available for growers to reduce the damage caused.

“Trials have shown results can be very good, and equal to the nematicides previously used for the purpose.

“However, when wireworm is the only target soil pest, the Nemathorin application rate is just 15kg/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 overdiluting the treatment. It needs to be accurately applied and evenly incorporated into the top 15-20cm 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.

“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.”

Future option

While Nemathorin is the best current option, Andy adds that new developments 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, has shown excellent results.

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,” he adds.

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