Small grain-Wheat stem sawfly

Cephus cinctus

Pest description and crop damage Primarily a pest in Montana and southeastern Idaho. Adults are wasp-like black-and-yellow insects with smoky dark wings. They typically rest on wheat stems facing the ground. The larvae feeds inside the stem and through the process fill the hollowed stem with frass. This symptom is visible when stems are split open. The larva typically stays in an "S-shaped " position when removed from the stem. The larva overwinters in protective thin cover at the very base of the crown stubs. Lodging is the most visible damage by the larval feeding, which could result in considerable yield loss.

Management- cultural control

Tillage is expected to reduce the survival of the larvae as it would result in desiccation and interfere with overwintering. Barley, oat and rye can be planted as trap crops along the edges. While oat is a nonhost to the pest, wheat stem sawflies are unable to complete their development in barley and rye.

Solid stem wheat cultivars are effective in reducing losses to wheat stem sawflies. Consult your crop advisor, extension educator, or specialist to select recommended varieties for planting in your region.

Management-chemical control

Foliar sprays

  • zeta-cypermethrin (Mustang) at 0.04 to 0.05 lb ai/a. PHI 14 days, also for forage and hay. REI 12 hr. Use for adults. Retreatment interval 14 days. Do not exceed 0.25 lb ai/a per year.
  • zeta-cypermethrin/chlorpyrifos (Stallion) at 0.22 to 0.28 lb ai/a. PHI 14 days for forage or hay; 28 days for grain and straw. REI 24 hr. Retreatment interval 14 days. Do not allow meat or dairy animals to graze within 28 days of application. Do not exceed 0.05 lb ai/a zeta-cypermethrin or 0.5 lb ai/a chlorpyrifos per season. Wheat only.