Walnut Husk Fly

Walnut husk fly larvae tunnel through the outer husk of black walnut fruit, causing the husk to turn brown or black and become difficult to remove. Infested nuts develop dark staining on the shell and meat. Adult flies appear in late summer and lay eggs in developing husks. Western Washington has limited black walnut production, reducing the regional impact of this pest.

Remove and destroy fallen husks and nuts in fall to eliminate breeding sites. For small numbers of trees, place baited traps to monitor and suppress adult fly activity. Clean up all dropped fruit and husks before winter. Since this pest is not widespread in western Washington, chemical control is not standard practice.