Agriculture: Blueberry Pest Management Guidelines

Pacific Flatheaded Borer

  • Chrysobothris mali
  • Description of the Pest

    Pacific flatheaded borer is an occasional pest in the San Joaquin Valley. The adult beetle is about 0.4 inch long with a dark bronze body and coppery spots on the wing covers. A fully grown larva is light colored, with a prominent, flat enlargement just behind the head and a pair of triangular dark brown mandibles at the tip of the head. There is one generation each year.

    Adult pacific flatheadedborers are generally present in May and June. When spring months are warm, they may be seen as early as late March or early April.


    Feeding by Pacific flatheaded borer larvae weakens the cane, resulting in stunted growth or death of the cane. Adult beetles are attracted to stressed or damaged blueberry canes, particularly areas with pruning scars or sunburn. Adult female beetles lay eggs on the injured area, and larvae excavate tunnels just beneath the bark and bore through the cane. Excavations are usually filled with tightly packed, finely powdered sawdust. Later, these areas may crack and expose the mines.


    Pacific flatheaded borers are managed by pruning and maintaining healthy bushes. Applying pesticides for this insect is not recommended.

    • Each year, remove old canes that exhibit borer damage and train new canes to take their place.
    • Prune at a time of year and in a manner that prevents sunburn of canes to reduce borer damage.
    • After pruning, chip or remove prunings from the field before immature stages of the borer can complete their development.
    Text Updated: 04/14