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Oak Pests - A Guide to Major Insects, Diseases, Air Pollution and Chemical Injury

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Prionus imbricornis

Prionus laticollis

Importance. -- These root borers occur throughout the East. Roots of oak and other hardwood trees are often hollowed or severed. Open-grown trees and those weakened by disease are most susceptible. Young, vigorous trees are occasionally cut off at the ground.

Identifying the Insect (figure 28a). -- 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 (figure 28b).

Identifying the Injury. -- Because injury occurs to the roots below ground, correct diagnosis is difficult. The above-ground symptoms are gradual decline of the tree, characteristic of severe, prolonged stress, i.e., leaves sparse, small, and yellowish. Examination of roots reveal the burrowing larvae and root damage (figure 28c).

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.


Figure 28a
Figure 28b

Figure 28c

Figure 28. -- (a) Larva of Prionus species tunneling in root; (b) adult beetle of Prionus sp.; (c) root damage by Prionus sp.
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