Beware of flathead borer biting into nut crops

The damage to this tree is from a Pacific flathead borer.
Photo by James Solomon, USDA Forest Service

According to the University of California (UC), nut growers have reported higher infestations of the Pacific flathead borer in recent years. The pest, while not new to the state’s Central Valley, is becoming a recurring problem, with drought likely a contributing factor, according to UC. Known to cause damage to stressed, injured and sunburned trees, there is a disturbing trend of flathead borers attacking healthy trees as well.

Currently, no traps are available for growers to assess populations and chemical control options. Currently, UC recommends that nut growers and pest management advisors be aware of the life cycle and damage the flathead borer can cause and be on the lookout for emerging damage. in their orchards.

Fall through winter is the best time to investigate stem borer infestation because it is easier to detect in leafless trees. UC advises these confirmation practices:

• Inspect the orchard for dead and scarred branches infested with flathead borer and look for external signs of infestation (ie, wound feeding on larvae, fresh or old insect droppings).

• Look for brown sap that has oozed and spread over the surface of the bark of the infested part of the tree.

• Look for any visible wounds on branches and limbs of trees that are prone to sunburn, or have pruning wounds, or any other type of cracks and wounds.

• For young trees, check for damage to the trunk, especially on the south or west side of the tree. These sides are preferred for egg laying by females due to higher exposure to sun and heat. Carefully check the graft union and pruning wounds.

•Use a knife to peel the bark off a suspicious branch and look for feeding canals filled with frass (sawdust-like insect waste) and cream-colored larvae underneath. Keep in mind that larvae tend to move into the heartwood in late fall to overwinter and are harder to find. Larvae finds may be easier from June to August, when the larvae are feeding just under the bark in the cambium layer.

• Look for D-shaped beetle exit holes on infested walnut branches.


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