Elateridae

Skadan orsakas vanligen av knäpparlarver men kan även orsakas av andra djurarter.

Knäpparlarvsskada

Skadan utgörs av en gång in i knölen av varierande djup. Vid mycket kraftiga angrepp kan knölen bli helt genomkorsad av gångar. Gången kan vara 2-5 mm bred beroende på vilken art av knäpparlarver som åstadkommit den. När skadan inträffat kort före upptagningen, slutar gången trubbigt, medan skador åstadkomna på ett tidigare stadium oftast slutar i en spets.

Knäpparlarverna tillbringar ca 4 år i jorden innan de förpuppas. Skadorna orsakas under de två sista åren av larvernas utveckling. Larverna är allätare men föredrar gräsrötter. Första året efter vallbrott lever de därför till viss del på vallsvålen, varför skadorna vanligen blir starkast under det andra året.

Under vissa odlingsbetingelser erhålls betydande skillnader i angrepp mellan olika potatissorter. Vanligen angrips då King Edward VII starkare än Bintje. Övriga djurskador. Skador i form av grunda urätna gropar i knölens ytlager kan åstadkommas av nattflylarver, vilket är det vanligaste, men även av ollonborrlarver och sniglar. Snigelskadorna går ofta djupare in i knölen och yttrar sig i breda gångar, som slutar i en eller flera urholkningar inne i knölen. Snigelskador förekommer vanligen endast på tyngre, våtare jordar.

Worm injury

The injury is usually caused by wireworm larvae but can also be caused by other borers and worms.

Wireworm injury:

The injury takes the form of bore-holes of different depths in the tuber: in severe cases it can be criss-crosses with bore-holes. The bore-holes can be from 2 to 5 mm in diameter depending on the type of wireworm larva that caused them. When the injury is caused just before lifting, the bore-hole has a blunt end, while bore-holes made at an earlier stage usually have a pointed end.

Wireworm larvae spend about 4 years in the ground before they develop into chrysalises. The injuries are caused during the two years of the larva’s development. Although the larvae are omnivorous by nature, they prefer to eat grass roots. For the first post-larval year they therefore subsist to a great extent on the egg-envelope, for which reason the damage caused by them is usually severest in the second year.

Under certain growing conditions, considerable differences in the extent of attack can be noticed in different varieties of potatoes. In this context King Edward VII is usually attacked more extensively than Bintje. Other animal damages: Damage in the form of shallow grooves in the tuber surface can be caused by noctua larvae, which is most common, but also by cockchafer grub and snails. Snail damage frequently goes deeper into the tuber and manifests itself as wide bore-holes, which terminate in one or several cavities inside the tuber. Snail damage is usually only present in potatoes grown in heavier, moist soils.