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How to identify it
- The first sign is a new cane whose tip suddenly wilts and droops, with a tiny hole about 1 mm (1/25 inch) across near the tip where the maggot bored in, a swelling where it is feeding, and later a purple to blackish discoloration around the internal tunneling. There is no external girdle of the kind the raspberry cane borer leaves.[1][2][3]
- Slicing the wilted cane open shows a whitish, legless maggot with a narrow head end and a broad, blunt rear, 7 to 8 mm (about 1/4 to 1/3 inch) long when full grown, in a frass-filled tunnel.[1][2]
- The adult is a hairy gray fly 4 to 5 mm (about 1/5 inch) long with one pair of clear wings; it looks much like a house fly but smaller.[1][2]
- The puparium is oblong, about 1/5 inch long, and lies in the topsoil.[2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Raspberry horntail | A sawfly whose larva causes virtually identical wilting and swelling of caneberry tips, but its pale larva has three pairs of true legs and grows to about 9/10 inch, more than twice the length of a cane maggot; management is the same.[2] |
| Raspberry cane borer | A beetle whose attack leaves an exterior girdle on the cane; its activity in New Hampshire begins around July 1, whereas cane maggot wilting shows up from late May to mid-June with no external girdle.[1] |
Where it lives
Occurs in the northern United States and much of Canada, as well as Europe; documented from at least five New Hampshire counties and probably statewide there, treated as a caneberry pest by the Pacific Northwest handbook, and covered for California gardens by UC IPM.[1][3][2]
Biology and life cycle
There is one generation a year. The insect overwinters as a pupa in the topsoil, and the adult flies emerge in April (late April in UC IPM's account) to lay eggs on or into the tips of new shoots; the female inserts each egg into the tender cane with her ovipositor, leaving the tiny hole that is visible later.[2][3][1]
The maggot hatches and tunnels downward in the pith of the young shoot, then girdles the cane just under the bark. In New Hampshire the injury appears from about May 28 through mid-June when new canes are 1 to 6 inches high; in the Pacific Northwest canes are usually 1 to 3 feet long when attacked.[3][1]
By about the first of July the maggot is full grown; it drops to the soil to overwinter and pupate. Damage is usually worst toward field edges, especially those bordering woodland.[1][2]
Hosts are red raspberry most often, black raspberry (blackcap), loganberry and sometimes blackberry.[1][3][2]
Damage and signs
- Infested shoots wilt suddenly, droop and discolor blackish to purple where the maggot has girdled them, and the tunneled tip dies. The pest kills canes but does not appear to reduce fruit yield even when abundant; the Pacific Northwest handbook reports very little loss even with 60 to 70 percent of new canes infested.[2][3]
- By the time most growers notice the wilted tips it is too late to prevent that season's injury, and there is usually not enough damage to warrant spraying.[1]
Health risk
None of the sources mentions any effect on people; the fly is a plant pest only.[1][2][3]
Control
Prevention
Where significant injury recurs every year, destroying nearby unmanaged or wild brambles may reduce the fly population, and keeping plants vigorous with appropriate irrigation helps them tolerate the loss of a few tips.[1][2]
Sanitation
Remove wilted canes as soon as they are seen, cutting several inches below the wilted area and below any visible tunneling, or near the base; dispose of the prunings in covered containers or burn them. Pruning out infested canes when the injury shows can reduce the risk of attack the following year.[3][2][1]
Biological control
Parasitoid wasps keep the pest at low numbers in most years, provided broad-spectrum, persistent insecticides are not applied to the caneberries for any pest.[2][3]
Pesticides
No chemical control is advised. Insecticide labels do not list this species, treatment would have to be applied in mid to late May at the first sign of egg laying, and most insecticides pose some risk to non-target organisms, so UNH recommends ignoring the problem.[3][2][1]
Common questions
- Why did the tips of my new raspberry canes suddenly wilt in early June?
- In late May and June a sudden wilt with no external girdle, a pinhole near the tip and purple discoloration lower down is raspberry cane maggot; a maggot is tunneling inside and girdling the shoot.[1][2]
- Should I spray for raspberry cane maggot?
- No. It kills a few canes but does not appear to reduce yield, no insecticide is labeled for it, and by the time wilting shows it is too late; prune out and destroy the wilted tips instead.[2][1][3]
- Is it the cane maggot or the cane borer?
- Cane maggot injury appears from late May to mid-June with no visible girdle; the raspberry cane borer beetle is active later, around the first of July in New Hampshire, and leaves an obvious girdle on the outside of the cane.[1]
Sources
- University of New Hampshire Extension, “Raspberry Cane Maggot, Pegomya rubivora (Coquillett) [fact sheet] (Alan Eaton).” extension.unh.edu/resource/raspberry-cane-maggot-fact-sheet (accessed 2026-11-10)
- University of California Statewide IPM Program, “Raspberry Cane Maggot, Home and Landscape pest page.” ipm.ucanr.edu/home-and-landscape/raspberry-cane-maggot/ (accessed 2026-11-10)
- Pacific Northwest Pest Management Handbooks (Oregon State University, Washington State University and University of Idaho), “Blackberry and Raspberry-Cane maggot, Pacific Northwest Insect Management Handbook.” pnwhandbooks.org/insect/small-fruit/blackberry-raspberry/blackberry-raspberry-cane-maggot (accessed 2026-11-10)
- iNaturalist, “Pegomya rubivora taxon page (order and family).” www.inaturalist.org/taxa/63150 (accessed 2026-11-10)