The first spray should be applied about mid-July and continued twice thereafter at weekly intervals for a total of three applications. Some control may also be obtained during harvest. Collect the nuts before the maggots emerge from the husk and place them in tubs or buckets partially filled with water. The maggots will drown and the fly population will be greatly reduced during the following year. Traps may be available in some locations to help monitor walnut husk maggot activity.
Trapping is a good way to determine if flies are present in a planting.