Raspberry cane borer damage is visible and alarming when you first encounter it: a wilted, drooping growing tip on a healthy raspberry cane, with two neat rings of punctures an inch apart just below the wilt. This distinctive two-ring pattern is the female beetle's work — she girdles the cane in two rings to kill the tissue, then lays an egg in between the rings. The wilting tip is the result of the girdling, and the borer larva that will spend the next two years inside the cane is just beginning its work.
I don't grow raspberries at my Long Island property, so this guide draws on Cornell Cooperative Extension, Penn State Extension, and Clemson HGIC research.
The pest
The raspberry cane borer (Oberea perspicillata) is a long-horned beetle (Cerambycidae). Per Penn State Extension, adults are:
- 12–15mm long, slender
- Black with yellow thorax (the section between head and wing covers) marked with two black dots
- Antennae as long as the body, characteristic of long-horned beetles
The species infects raspberry (Rubus idaeus), blackberry (R. allegheniensis), and rose (Rosa spp.).
Identification
The two-ring girdling
Per Cornell Cooperative Extension, the female beetle girdles the cane by chewing two rings of punctures approximately 0.5–1 inch apart, about 6–8 inches below the growing tip. Between these two rings, she lays a single egg. The girdling kills the tissue above the lower ring; the growing tip wilts and collapses within days. The two-ring pattern is the most diagnostic sign of this specific pest.
Wilted tips ("flagging")
Per Penn State Extension, the wilted tip (commonly called "flagging") appears in June–July when adults are active:
- The top 6–10 inches of a primocane (first-year cane) wilts and hangs down
- The cane is otherwise healthy below the girdling point
- Multiple canes in a planting may show flagging simultaneously during adult flight periods
Larval boring
Per Clemson HGIC, after hatching, the larva:
- Year 1: bores downward through the pith of the cane, progressing toward the root crown
- Year 2: continues boring through the root crown, pupates in the crown in summer
- Second-year damage causes entire cane death and eventually crown damage if multiple larvae accumulate
Cutting a wilted cane segment in half longitudinally reveals the borer tunnel (a chamber in the pith). In Year 1 canes, the larva is typically just below the egg site; in Year 2, it will have progressed toward the base.
Life cycle
Per Penn State Extension:
- Adults emerge in June–July
- Females girdle canes and lay eggs; each female lays several eggs in different canes
- Eggs hatch in approximately 10 days; first-year larvae bore downward
- The pest has a 2-year life cycle (larva spends two growing seasons inside the cane)
Management
Prune wilted tips immediately
Per Cornell Cooperative Extension, the only effective management is prompt pruning of wilted tips. Cut at least 6 inches below the lower girdle ring (the lower of the two rings of punctures), back to healthy, unpitted pith tissue. This removes the egg or newly hatched larva before it descends into the lower cane.
- Identify the two ring-girdling pattern before cutting to confirm the pest
- Make cuts 6 inches below the lower ring to ensure removal of the egg/larva
- Inspect for pith tunneling at the cut surface: if you see a tunnel, cut lower until you reach solid pith
- Dispose of the cut tip in the trash — do not compost
Per Penn State Extension, daily or every-other-day inspection during June–July for flagged tips and prompt removal is the most effective management program for home raspberry plantings.
Remove second-year infested canes
Per Clemson HGIC, in late winter, inspect all canes for visible boring damage (a small entry hole at the pith of a cut floricane or old cane) and remove infested canes at the soil line. This eliminates larvae that survived Year 1 and prevents second-year boring into the crown.
Insecticides
Per Penn State Extension, insecticide applications are generally not effective or recommended for raspberry cane borer because the larvae are protected inside cane tissue within days of egg-hatch, and adult beetles are difficult to intercept with contact sprays. The pruning approach is more effective and creates no pesticide residue on edible fruit.
Common problems table
| Symptom | Likely cause | Action |
|---|---|---|
| Wilted tip with two rings of punctures below | Raspberry cane borer girdling | Prune 6 inches below lower ring; dispose |
| Wilted tip with no visible puncture rings | Drought stress or Phytophthora crown rot | Check soil moisture; examine crown |
| Dead cane with a pith tunnel inside | Second-year cane borer | Remove cane at soil line; dispose |
| Multiple flagged tips in June–July | High adult population year | Daily inspection; remove flagged tips promptly |
| Crown damage with multiple dead canes | Accumulated multi-year boring | Remove all infested canes; monitor closely |
Frequently Asked Questions
Why does my raspberry have new wilted tips every year?
Per Penn State Extension, adults emerge annually in June–July and lay eggs in new primocanes each year. Even after thorough pruning, new adults (from larvae that were not removed or from adjacent properties) will girdle new canes the following season. Annual June–July inspection and pruning is therefore an ongoing practice, not a one-time fix.
Can the two rings of punctures be confused with anything else?
Per Cornell Cooperative Extension, the double-girdle pattern is highly distinctive and unlikely to be confused with other damage. Mechanical injury or other boring insects do not produce this two-ring pattern just below a wilted tip.
Does raspberry cane borer affect blackberries?
Per Penn State Extension, yes — the same species infests blackberry canes with identical symptoms. Rose cane borer (Agrilus rubicola), a different species, produces similar damage on roses.
How many cane tips can one female girdle?
Per Clemson HGIC, a single female typically girdles and oviposits in multiple canes during her active period. In high-population years, 10–30% of primocanes in a planting may show flagging. Aggressive pruning during adult flight reduces the second-year population accordingly.
Recommended gear: Best bypass pruners: Felco vs Corona vs ARS — our buying guide, with picks weighed against university Extension guidance and product labels.
Sources
- Penn State Extension — Raspberry Cane Borer
- Cornell Cooperative Extension — Raspberry Pest Management
- Clemson HGIC — Raspberry Insects