Flagged branches are a symptom of pales weevil feeding. Courtesy of Sandy Gardosik, PDA
Hylobius pales (Herbst)
- Pines preferred, Scotch more so than eastern white
- Occasionally on Douglas-fir, fir, spruce, and other conifer species
Symptoms and Signs
- Dead seedlings with missing bark near soil line
- Small holes or pits in the bark from feeding that may fi ll with resin if infestation is light
- Yellow needles at branch tips that turn reddish brown, giving the tree a “flagged” appearance; bark will be missing behind the dead tissue
- White, C-shaped larvae under the bark of stumps and roots
- Adult weevils in the leaf litter surrounding trees or on stumps in early spring
Causes of Similar Symptoms
- Eastern pine shoot borer
- Diplodia (Sphaeropsis) shoot blight
- Northern pine weevil
- White pine blister rust
- Pine shoot beetle
- Wood borers
- Bark beetles
The adult pales weevil is a large, robust insect measuring ¼–2⁄5 inch (6–10 mm) long with a prominent snout. The weevil is black to dark reddish brown in color with very small patches of yellow-white scales on its head and wing coverings. In early spring, adults are frequently found on and around 1- to 2-year-old stumps. The larvae are cream colored, legless, and “C” shaped. They have a light brown head capsule and are found burrowed into the cambium tissue of stumps and roots.
Adult pales weevils are particularly damaging to eastern white pine, Douglas-fir, and true firs. The weevils feed on terminal shoots, consuming the bark down to the wood and girdling and killing the shoot. This flagging can seriously disfigure marketable trees (Figure 1). Larval feeding is generally restricted to 1- to 2-year-old stumps and dying trees of Scotch, Austrian, and red pine. Larvae and pupae may be found on larger roots below the soil surface. Larvae pupate in chambers plugged with wood fibers.
Figure 1. Evidence of weevil feeding indicated by flagging. Courtesy of Rayanne D. Lehman, PDA
Biology and Life Cycle
Pales weevils overwinter as adults in the soil and become active between April and June (Figure 2). They feed for several weeks on seedlings and the tender bark on twigs of more mature trees (Figures 3 and 4). Feeding occurs at night, while the weevils take refuge in the leaf litter and under logs during the day.
Figure 2. Adult pales weevil feeding on bark of a twig after spring emergence. Courtesy of PDA
Figure 3. Weevil feeding damage on eastern white pine branches. Courtesy of Brian Schildt, PDA
Figure 4. Weevil feeding damage on Fraser fir leader. Courtesy of Rayanne D. Lehman, PDA
After feeding, the weevils mate and females lay pearly white eggs in the subterranean roots of pine stumps or dying trees. Eggs hatch within 10–14 days and the larvae feed beneath the bark until they mature in early fall (Figure 5). The larvae pupate in a chip cocoon (Figure 6) before emerging as adults in August–October. These adults feed for 2–3 weeks before seeking overwintering sites in the soil around fresh-cut stumps or beneath dying trees. One generation occurs per year.
Figure 5. Larvae feeding under the bark of a stump. Courtesy of Rayanne D. Lehman, PDA
Figure 6. Chip cocoon created by larvae before pupating into adults. Courtesy of PDA
Calendar of Activities
Monitoring and Management Strategies
- Delay planting for 2 years in an area where pines were recently harvested.
- Remove and destroy stumps.
- Treat stumps from the previous season’s harvest before adult weevils become active in spring.
- Destroy culled tree piles before pales weevils become active in spring. These weevils are attracted to the resins and will fly up to several miles to seek breeding material. Traps deployed to monitor for white pine weevil will also attract pales weevil adults.
- Growing degree days: Treat stumps with insecticide to prevent egg laying at 7–121 GDDs.
- Scout for the presence of different life stages of the weevil.
— For adults: Lay a sheet out under a tree after dark and shake the tree. Look for weevils that fall from the tree to the sheet.
— For larvae and pupae: Use a knife to cut back the bark on stumps or the base of dead trees to look for larvae burrowing through the tissue or pupae in chip cocoons.
- Scout 50 random trees of any age for seedling injury and branch flagging.
— If seedlings show any weevil injury or older trees average more than five flagged branches, consider treating the entire plantation.
- At the end of the season, evaluate results and update records.
- No recommendations are available at this time.
- Remove and burn or chip stumps and debris.
- No recommendations are available at this time.
- Dip new seedlings (above ground portion) in appropriate insecticide before planting.
- In early spring, apply an approved pesticide to stumps from previous cutting season. Stumps older than 2 years do not need to be treated.
- If a population is extremely high, apply an appropriate insecticide to mature trees in spring between April and May and again in August and September to kill bark-feeding weevils.
- Remove cut stumps or treat stumps with an insecticide before replanting a field.