Mint-Mint stem borer

Pseudobaris nigrina

Pest description and crop damage Adults look like weevils. Larvae are small white grub, 0.08 to 0.16 inch long, with a brown head and no legs. Damage is to the main root; females bore into the base of a stem laying a single egg at the base of stock. Larvae hatch, feeding on tissues of the main stalk, causing injury or death to the central stalk, which usually breaks off. A female lays approximately 100 eggs per season. It is found in eastern Oregon and Idaho. It can infest mint rootstock for export.

Management-chemical control

No insecticides are registered. However, aphid or looper sprays applied in mid- to late May generally reduce stem borer populations.