Tilehorned Prionus
Prionus imbricornis (Linnaeus)
Broadnecked Root Borer
Prionus laticollis (Drury)
J. D. Solomon, F. I. McCracken, R. L. Anderson, R. Lewis, Jr., F.L. Oliveria, T.H. Filer, and P.J. Barry
Importance – These root borers occur throughout the East. Roots are often hollowed or severed. Opengrown trees and those weakened by disease are most susceptible. Young, vigorous trees are occasionally cut off at the ground.
Identifying the Insect – Larvae of both species are fleshy, creamy white with three pairs of small legs. They have cylindrical bodies and attain lengths of up to 3 inches (75 mm). The adult beetles are robust, broad, dark brown, somewhat flattened, and up to 1.5 inches (37 mm) long .
Identifying the Injury - Because injury occurs to the roots below ground, correct diagnosis is difficult. The aboveground symptoms are gradual decline of the tree, i.e. leaves sparse, small, and yellowish, which is characteristic of severe, prolonged stress. Examination of roots reveals the burrowing larvae and root damage.
Biology – Adult beetles emerge from the soil in early summer and deposit 300 to 500 eggs in the soil. Young larvae burrow through the soil to the roots and begin feeding. The feeding period lasts 3 to 5 years.
Control – Disease, drought, mechanical injury, and poor soil conditions increase tree susceptibility. Therefore, follow cultural practices that will keep trees thrifty and vigorous. Insecticides are seldom needed.
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