Prionus Borers

    Prionus Borers

    Prionus spp.

    prionus borers

    Female (left) and male (right) prionus root borers (Diane Alston, Utah State University Extension)

    prionus borer larvae

    Prionus root borer larvae (Diane Alston, Utah State University Extension)

    prionus borer damage

    Prionus borer root furrowing (Diane Alston, Utah State University Extension)

    prionus borer damage

    Canopy dieback due to prionus infestation (Diane Alston, Utah State University Extension)

    Pest Description

    • adults: large, 1 3⁄4 – 2 1⁄4 inches; reddish brown, relatively smooth with deeply notched antennae
    • larvae: up to 4 1⁄4 inches long and about 3⁄4 inch in diameter; legless and whitish in color

    Host Plants, Diet & Damage

    • sweet cherry, peach, apricot, other stone fruits, cottonwood and other ornamental trees and shrubs
    • larvae feed on roots, reducing the tree’s ability to take up water and nutrients
    • larval feeding can open up trees to root rot pathogens
    • feeding in the root crown and upper roots can girdle trees
    • cause limb dieback and overall reduce tree vigor
    • infestation and damage are worse on sandy soils

    Biology, Life Cycle & Damaging Life Stage

    • overwinter as larvae in the roots or soil
    • pupate in spring
    • adults emerge and fly July to September
    • eggs are laid in soil near host trees
    • larvae move into the soil and feed on roots working their way upward toward the root crown
    • in the third year, larvae pupate near the soil surface next to root crowns
    • one generation is completed in 3 years
    • larvae are the primary damaging stage

    IPM Recommendations

    • Manage trees to improve or maintain overall health.
    • Monitor beetles with a pheromone and bucket light trap.
    • Monitor trees for canopy dieback.
    • Apply an insecticide (carbamate; pyrethroid) to the lower trunk and soil to target adults and inhibit egg laying.
    • Apply a systemic neonicitinoid to the root zone to suppress younger larvae.

    For more information, see our Prionus Root Borer fact sheet.