Prionus Borers

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.