Improved monitoring and control of wireworms (Coleoptera: Elateridae) in Norwegian potato production

Wireworms are larvae of several click beetle species that live in the soil and feed on roots, stems and tubers of various plants, which causes holes and tunnels in the tubers rendering them unmarketable. In Canada and Germany there is substantial economic loss from wireworm attack in potatoes. Norwegian potato growers are not well prepared for an increased level of damage. There is insufficient understanding of the species and their distribution, there are no registered pesticides and alternative control methods are not developed for this pest. The goal of this project is to combine several methods according to the principles of Integrated Pest Management (IPM) to mitigate the reduction in yield and quality from wireworm attack. In autumn 2019 the Canadian wireworm expert Dr. Vernon held a workshop in Ås. The aim of the workshop was to increase the capability of the Norwegian project participants for identification of click beetles and wireworms and to set standardized criteria for evaluating wireworm damage on potato tubers. Click beetles were collected in 2019 and 2020 using both unbaited and pheromone-baited pitfall traps to give an overview of the species that cause damage in Norway. The traps were placed in the verges of the potato fields from the end of April to mid-July. The trap catches have given us valuable information on the species found in the vicinity of potato fields. Wireworms were collected from within the potato fields using bait traps in the soil. Traps were placed at 5 different locations in southern and eastern Norway in the spring and autumn of 2019 -2021. In addition, wireworms have been collected with bait traps in farmers potato fields by regional extension units (NLR) in northern Norway, in northwestern Norway, and in potato cultivar field trials. Further on, wireworms collected by hand at harvest by potato growers have been sent NIBIO for ID. All the specimen collected have been identified to species level. Results show there are additional species involved in the damage to potato crops than previously known, and that 3 of these are dominant when it comes to numbers caught. Often more than one species is present in the field, and the species composition differs between fields and years. One method to prevent damage from wireworms is to use potato cultivars that are resistant to damage. To find out if cultivars used in Norway are resistant to wireworms, field experiments were performed at Sunndalen, Apelsvoll, Sør-Odal, and Råde in 2019-2021. The trials included the cultivars Asterix, Fakse, Folva, Mandel, Nansen, and Pimpernel. The harvest from the trials was sent to NIBIO Apelsvoll and evaluated for wireworm damage and symptoms. The results indicate a slight difference between the cultivars tested, with Asterix being most susceptible followed by Fakse and Folva. The most important method for prevention of wireworm damage is crop rotation to limit oviposition and the development of large numbers of larvae. We have conducted a literature search to learn as much as possible about the experience with crop rotation and practices in general concerning wireworms in other countries. We have also specifically looked at a Canadian system for risk assessment of wireworm damage to fields. Wireworm risk to the field is calculated based on field crop history and nearest wireworm damage in the past 4 years. The usefulness of this approach has been evaluated by NLR. The conclusion is that this specific risk assessment doesn’t work as well under Norwegian conditions, probably due to different crop rotation strategies and wireworm species composition in the fields compared to Canadian fields. We have been testing a method for biological control of wireworms in potatoes using ATTRACAP®. This system uses CO2 to attract wireworms, which are then killed by the insect-pathogenic fungus Metarhizium brunneum. In 2019 we tested the effect of 3 Norwegian strains of this fungus against wireworms in lab experiments. The strain that performed best at low temperatures (equivalent to temperatures in Norway at planting) was chosen for further testing. The German company BIOCARE has produced ATTRACAP® using this strain for better performance in Norwegian conditions. We have had field experiments in 2019-2021 at 5 potato farms in the southern and eastern part of Norway in cooperation with local NLR units. In 2019 only the original ATTRACAP® was tested, while in 2020 and 2021 both the original ATTRACAP product and the modified version with the Norwegian M. brunneum strain was tested. ATTRACAP with the Norwegian strain of M. brunneum give promising results as a potential biological control agent against wireworms under Norwegian conditions. Damage grading of tubers at potato packing lines and in field trials at potato producers confirms that damage caused by wireworms differ greatly between fields and between years, with the damage ranging from below 1 % up to 60 % damaged tubers.

Prosjektet har bidratt med ny og viktig kunnskap om hvilke arter av smellerbiller (kjølmark) som forårsaker skade på potet i norsk potetproduksjon. Artskunnskap er en viktig del av en IPV-strategi for å kunne gjøre riktige tiltak til riktig tid. Det er framskaffet mer kunnskap om ulike potetsorters mottakelighet overfor kjølmarkangrep, og det foreligger et veldig lovende preparat for biologisk bekjempelse av kjølmark under norske forhold. Preparatet er basert på en insektpatogen sopp som angriper og dreper kjølmarken uten bruk av kjemiske plantevernmidler. Dette er gunstig både for miljø og helse. Resultater fra registrering av kjølmarkskade i Norge bekrefter at det er stor variasjon når det gjelder skadeomfang, og at det er et stort potensial for en utvikling lik den vi ser ellers i Europa der det er store utfordringer med angrep av kjølmark. Det har ikke lykkes oss å etablere et beslutningsstøttesystem i Norge basert på den kanadiske risikobedømmingen. Likevel har prosjektet bidratt med kunnskap om metoder som kan benyttes for å undersøke forekomst av kjølmark på et gitt areal. Bruk av lokkefeller om våren eller høsten året før planlagt potetdyrking, kan gi indikasjon på om det foreligger fare for å få angrep av kjølmark året etter. Dermed kan produsenten få et bedre beslutningsgrunnlag for for å vurdere hvilket areal som egner seg best for potetdyrking, og dermed redusere avlingstap og kvalitetsforringelse som følge av kjølmarkskade. Kjølmark spiser på røtter og knoller av mange ulike vekster. Deler av kunnskapen framskaffet i prosjektet vil også være gyldig ved dyrking av andre kulturvekster i Norge. Prosjektet har i tillegg bidratt til økt internasjonalt forskningssamarbeid, samt nettverksbygging mellom ulike aktører innen forskning, rådgivingstjeneste og potetnæringen i skandinavia og deler av Europa.

Wireworms are soil-dwelling larvae of click beetles, of which some are important pests of crops like potatoes, cereals and root crops. In potato tubers and root crops, the larvae reduce yield and quality by making holes, tunnels or surface wounds and scars. Until the 1990s, wireworm control relied mainly on the use of synthetic insecticides. Most of these are now banned, mainly due to environmental and health issues. In Norway, damage from wireworms has so far been a minor problem, but are now increasing at an alarming rate. However, updated knowledge of which wireworm species that are most damaging in Norwegian potato production, their life-cycles and host preferences, are lacking. At present, direct and effective pest control tools are missing, and alternative methods to reduce the wireworm populations are needed. On this background, our main objective is to present a robust integrated pest management system (IPM) for monitoring and control of wireworms in potatoes. To reach this goal we will use traps and pheromones to attract, collect and identify click beetles and wireworms from growers' fields, to learn which wireworm species that are most important, where they are most abundant, and how they develope. In field trials, we will test if the resistance to wireworms differ between commonly used cultivars, so that the least susceptible could be used in IPM. As potatoes usually are grown in a rotation system with other crops like grasses, cereals and root crops, we will also study how this may influence the potential damage in a given season. Finally, a promising method for direct biological control, by combining an attractant (odour) and a killing component (pathogenic fungal isolates), will be tested in field experiments at different growers' locations. The knowledge and methods developed from each of these project activities, will be integrated in an IPM system, and contribute to reduce the risk of wireworm damage in the growers fields.