Pest description and crop damage The adult is a very small fly, about 1-3 mm long, and reddish. Larvae are white to orange, very small and difficult to see with the naked eye. The larvae feed on developing shoot tips, causing distorted growth. Damage may be confused with boron deficiency or even with normal black tip stage of development. Terminal growth feeding releases apical dominance and will often cause branching and a witches-broom appearance. Bud damage at an economic level has not been observed in the PNW.
Biology and life history This insect overwinters in the pupal stage in the soil. In the spring, the female emerges and lays eggs in either floral or vegetative buds just after bud swell, when bud scales begin to separate. Eggs hatch into larvae within a few days and begin feeding within the blueberry bud. After about a week of feeding, these larvae drop to the soil and form puparia. There may be up to four generations per year.
More information is available in the OSU Extension publication EM 8889, Blueberry Gall Midge-A Possible New Pest in the Northwest (https://extension.oregonstate.edu/catalog).
Management-chemical control: HOME USE
- pyrethrins-Some formulations are OMRI-listed for organic use.
- spinosad-Some formulations are OMRI-listed for organic use.
- zeta-cypermethrin-Toxic to bees; do not apply when bees are foraging.
Management-chemical control: COMMERCIAL USE
Note: The following recommendations are legal pesticide uses even though blueberry gall midge may not be listed on the pesticide label.
- cyantraniliprole (Exirel) at 0.088 to 0.133 lb ai/a. PHI 3 days. Note "Bee Advisory Box" and restrictions on the label.
- diazinon (several brands) at 0.5 lb ai/a. PHI 7 days. One application per season allowed; as such, consider other pests that may need to be managed with diazinon. Restricted use pesticide.
- malathion (several brands) at 1.25 lb ai/a. PHI 1 day.
- methomyl (Lannate) at 0.45 lb ai/a. PHI 3 days. Restricted use pesticide.
- novaluron (Rimon 0.83EC) at 0.13 to 0.19 lb ai/a. PHI 8 days. Apply when larvae are young and small.
- spinetoram (Delegate WG) at 0.05 to 0.09 lb ai/a. PHI 3 days. Provides suppression only. SLN 24c OR-170016 for Delegate allows a 1-day PHI in Oregon only; read label carefully for restrictions on number of applications allowed.
- spinosad (Entrust) at 0.062 to 0.1 lb ai/a. PHI 3 days. SLN 24c OR-160013 and WA-140014 for Entrust SC formulation allow a 1-day PHI in Washington and Oregon only. Entrust is OMRI-listed for organic use.
- spirotetramat (Movento) at 0.13 to 0.16 lb ai/a. PHI 7 days. Do not apply during bloom.