Image by Whitney Cranshaw, Colorado State University, Bugwood.org

Rose curculio

damaging

Rose curculio damage to buds. Image courtesy of Courtney Manusson

The ‘Rose curculio’ aka ‘Rose weevil’ (Merhynchites bicolor) can cause damage to roses, and less commonly, raspberries. The adult weevils are black with a red back and long snout, and are about 8 mm long. They chew holes in rose buds to feed on pollen inside and will also feed on flowers and rose hips as well as the tips of rose canes. The weevils lay eggs inside the buds, which hatch into larvae, which continue to feed. The larvae fall to the ground and overwinter as pupae around the base of the plants.  There is one generation per year.

Control:

  • Examine buds for holes. Cut open a few of the buds to see if there are larvae inside. If there are no larvae, they may already be in the soil. Larva will leave frass (excrement) inside the bud.
  • Prune out all of the affected buds. Place the debris in the garbage, not the compost
  • Scout for the adult weevils in early June. Hand-pick and destroy, or vacuum them up with a shopvac if you have lots of them. Another way is to gently shake flowers over a bucket soapy water to collect fallen adults.
  • To break the insect life cycle, place a light coloured sheet or tarp under the shrub to prevent the larvae from burrowing into the ground to over winter.

Source:

http://ipm.ucanr.edu/PMG/GARDEN/PLANTS/INVERT/rosecurculio.html