OSU Extension Catalog

Pest identification

• Adults are 2 to 11 mm (1∕16 to 1∕2") in length.
• Typically brown or black in color
• Larvae are C-shaped, legless grubs with a brown head and white body.

Biology and life cycle

• Root weevils can cause significant crop loss as well as cause load rejection for Christmas tree exporters.
• Late-stage weevil larvae are present in late spring and summer.
• Larvae feeding on tree roots cause the most damage.
• Pupae occur from late May into early June.
• Adults are present year round.
• Adults typically feed on needles at night.
• Adults can girdle seedlings and small trees.
• Adults lay eggs in soil 4 to 6 weeks after their emergence.
• Individuals of most species are all egg-laying females.
• There is one generation per year.
• Barypeithes pellucidus and Otiorhynchus spp. were accidentally introduced from Europe. Nemocestes spp. and Sciopithes obscurus are native.

Noble fir most susceptible, followed by Douglas-fir, grand fir, Nordmann fir, and Turkish fir

Growing years

• Look for adults on cloudy days and at night on branches and trunks; use beating boards and sheets. (See Overview of Trapping and Monitoring Options.)
• Look for notching of needles and girdling of small trees and branches (evidence of adult feeding).
• Place pitfall traps in the field for monitoring. (See Overview of Trapping and Monitoring Options.)
• Check for adults during the day under pieces of plywood placed on the ground overnight (similar to slug monitoring).
• Dig with a shovel around roots to monitor for larvae.
• Note: Evidence of digging by insect-eating mammals can be an indication of the presence of larvae.

At harvest

• Look for adults on trees that show evidence of notching on needles.
• Look for adults on cloudy days or at night on branches and trunks.
• Use pitfall traps or check under pieces of plywood placed on the ground.

Threshold

• Some trading partners, such as Mexico, Japan, and Hawaii, have zero tolerance for some or all root weevil species.

Growing years

• Apply pesticides as adults become active and before egg laying occurs. (Visit the PNW Insect Management Handbook.)
• Apply labeled insecticide in the evening during peak adult activity in May to June.
• Disrupt habitat (for example, by disking or tilling in the summer and fall) to reduce populations.
• Reduce shelter and additional hosts by controlling weeds around loading areas.
• Preserve populations of rove and other naturally-present ground beetles, as they can be important biological control agents.
• Note: Nematodes and fungi have been used as biocontrol agents in Christmas trees.

At harvest

• Shake trees according to compliance agreements for destination countries. (See Best Management Practices at Harvest.)
• Keep trees off the ground at harvest, especially after shaking. Trees left overnight on the ground are very vulnerable to root weevil infestation.
• Do not place trees near shaking debris; remove debris frequently.

Life cycle

Management