Beware of the flathead moth that bites nut crops

Damage to this tree is caused by a Pacific flathead borer.
Photo by James Solomon, USDA Forest Service

Nut growers in recent years have reported higher infestations of the Pacific Bull Moth, according to the University of California (UC). The pest, while not new to the state’s central valley, is becoming a re-emerging problem, with drought likely a contributing factor, according to UC. Known to cause damage to stressed, injured, and sunburnt trees, there is a worrying trend of flathead borers attacking healthy trees as well.

Currently, there are no traps 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 check for borer infestation as it is easier to detect in leafless trees. UC recommends these confirmation practices:

• Scout the orchard for dead and reported branches infested by the Flathead Borer and look for signs of external infestation (ie.

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

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

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

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

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


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