Name: Phthorimaea operculella Zeller

Alias: Potato tuberworms hatch as larvae in the late summer to early fall and get nice and fat before overwintering either on potatoes left on bare soil or in a potato cellar. Larvae prefer the upper canopy of potato plants, but they feed throughout the plant. They pupate in the spring and emerge as fully grown adult tubeworm moths. Adults are a gray-brown with dark spots on them. They seek out mates almost immediately after emerging and lay eggs on potato plants where the larvae can feed once they emerge.

Crimes: Potato tuberworms start out as leaf miners, feeding inside the leaves. As they mature, they work their way into stems and eventually any shallow or exposed tubers. Leaf and stem damage are significant, but the primary concern is the damage to the actual potato. Damaged potatoes are unmarketable, but damaged material can be cut off.

Redeeming Qualities: None known.

Sentence: Populations of potato tuberworms may exist in the field, but it may not be economically worth taking action. Damage to plants should be monitored, as well as traps containing tuberworm pheromones. Make sure volunteer potatoes are cleared out of the field each year. Make sure that you plant potatoes deep enough that they are not exposed and eliminate any practice that causes exposure. With severe populations, pesticides may be applied one to four weeks before vine kill to reduce damage. Always read and follow label instructions when using any pesticide.

For more information on dangerous and beneficial bugs, call UI Extension educator Joseph Sagers at 208-745-6685 or email

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