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Prionus borers

Prionus laticollis (Drury)
Prionus imbricornis (L.)

Coleoptera: Cerambycidae

Broadnecked root borer, Prionus laticollis (Drury)
Tilehorned prionus, Prionus imbricornis (L.)

Adults are robust, broad, somewhat flattened blackish to reddish brown beetles with antennae roughly half the length of their bodies (A). Larvae are large, fleshy, elongate grubs, creamy white to yellowish in color, with 3 pairs of small legs, a swelling behind the small head capsule, and strong black mandibles (B).

Distribution

Most fruit-growing states and provinces in eastern North America.

Damage

Attack apple, cherry, peach and plum. Larvae of both species feed on the wood of roots and crown, which they hollow, girdle or sever (C, D); the larval stage can last three years or more. Affected trees show a gradual thinning and yellowing of foliage and limb-by-limb mortality. Young trees can be chewed off just below the surface; established trees may have only 1 or 2 roots left intact and can be blown over by wind.

Management

Keep base of trees free from weeds to encourage predators; use oviposition barriers of netting or screening on bottom 30–60 cm (12–24") of trunks. A surface deterrent or insecticide can be sprayed on trunks in early summer.

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The MSU IPM Program maintains this site as an access point to pest management information at MSU. The IPM Program is administered within the Department of Entomology, fueled by research from the AgBioResearch, delivered to citizens through MSU Extension, and proud to be a part of Project GREEEN.