Cull onion disposal is required by March 15 in six southwest Idaho counties.

All cull or waste onions not suitable for human consumption must be disposed of by an approved method by the deadline in Ada, Canyon, Gem, Payette, Owyhee and Washington counties, according an Idaho State Department of Agriculture news release. After March 15, onions that are sorted must be disposed of within a week.

The cull disposal deadline, referenced in a state rule, is intended to protect the industry from onion maggot.

Onion maggot is a fast-reproducing pest that damages onion crops. Larvae feed on roots of germinating seedlings and later on expanding bulbs, which can severely reduce yields, according to the department. Feeding damage also provides an avenue for pathogens to rot bulbs during storage.

ISDA inspectors will monitor cull disposal sites. Approved disposal methods include pit burial, feeding, composting, spreading, chopping and shredding.

The state rule references the University of Idaho Best Management Practices for Pit Disposal of Cull Onions publication, available through UI Extension.

Southwest Idaho and southeast Oregon comprise a major onion production region.

Information: ISDA, 208-332-8620.