Do it yourself - Blueberry maggot monitoring

I have received several questions from growers and homeowners about blueberry maggot monitoring and management over the last few weeks. As part of an ongoing research project, my lab continues to monitor blueberry maggot populations in North Carolina blueberry fields. Our methods were based on those accepted by the Canadian Food Inspection Agency, and can readily be used by growers or homeowners. This post details how interested growers and homeowners can monitor blueberry maggot populations in their blueberry planting.  You can learn about blueberry maggot biology here.

Note that all supplier links are provided for informational purposes. This information is not intended to endorse any particular supplier over another.

What will I need?
Yellow sticky traps (Trece AM-No Bait traps preferred)
Bulk ammonium bicarbonate and vials or "bait enhancers"

From left, bait enhancer vial, AM-No Bait Trap, and bulk ammonium bicarbonate.  Photo: HJB

How many traps do I need?
Trap number depends on the size of your planting. You should always use a minimum of 3 traps for plantings of 5 acres of less. For plantings larger than 5 acres, use the table below (adapted from the Phytosanitary Requirements for the Importation From the Continental United States and for Domestic Movement of Commodities Regulated for Blueberry Maggot, Canadian Food Inspection Agency):

Area of Blueberry Planting (Acres)	Number of Traps
5 or less	3
6-15	4
16-40	5
41-70	7
71-100	9
Over 100	9 + 1 trap for every additional 15 acres over 100

How do I place the traps?

Blueberry maggot traps should be hung in the upper third of blueberry bushes so that they are clearly visible.  Traps should be hung with the folded end pointed down and the opening upward.  Ammonium baits should be attached to the trap via a twist tie.  Previous research in North Carolina has demonstrated that blueberry maggot adults are more often trapped in large plants and shaded areas.  Therefore, large blueberry bushes with fruit present are preferred for trapping.  Some traps should also be placed near the edges of fields/plantings in weedy areas.

Blueberry maggot trap in blueberry planting in Rockingham County, NC. Photo: HJB

How do I check traps?
Traps should be checked a minimum of once per week, ideally twice per week.  At each trap check, you should also check the ammonium lure.  If you no longer smell ammonia, replace the ammonium bicarbonate.  We typically need to replace the ammonium bicarbonate weekly, so plan for this when you order supplies.  Check for blueberry maggot flies on traps.  Blueberry maggot flies are about half the size of a house fly and have a distinctive "w" pattern on their wings.  Cornell Cooperative Extension has developed a nice fact sheet with photos of other commonly caught flies that may be confused with blueberry maggot.

Remove traps with blueberry maggot flies from your planting and replace with new traps.  If you are new to monitoring, save your traps and have you identification confirmed by your county cooperative extension agent or extension specialist.

We found that we could leave traps in the field for 3 to 4 weeks before they become soiled or full of insects.  Change traps at least every 4 weeks, sooner if they are no longer sticky or the color is obscured by insects, debris, or dirt.

Blueberry maggot adults captured in an AM-No Bait trap.  Photo: HJB

What do I do if I find blueberry maggot flies?
Your management strategy for blueberry maggot will likely differ depending upon the fate of your fruit.  For commercial growers exporting to Canada, you must treat within 7 days of blueberry maggot fly capture.  At least 2 treatments, 7 to 10 days apart must be applied until flies are no longer captured.  Consult the NC Agricultural Chemicals Manual for information on registered insecticides for blueberry maggot.  Be sure to check with your marketer before using any insecticide to ensure that it is acceptable.  This process is repeated if new flies are caught.

For commerical growers not exporting to Canada, the above strategy is also likely the most appropriate, but you may choose different insecticides.

For organic commercial growers, the choices are limited to spinosad (GF-120 & Entrust) and kaolin clay (Surround).  Because there are restrictions on the number of applications of Entrust, one of the more effective insecticides, monitoring is even more important to ensure that unnecessary applications are not made.

For homeowners, check with your local cooperative extension agent for insecticide options and consider using Surround.  Surround coats the fruit with a layer of clay that interferes with fruit detection and egg laying.  This coating readily washes off, but is often not suitable for commercial growers who do not wash their fruit prior to packing it.  Because Surround acts as a barrier, it will need to be reapplied after rain.

What else do I need to monitor?
Growers monitoring for blueberry maggot should also strongly consider monitoring spotted wing drosophila (SWD) at the same time.  Look for a SWD monitoring post to follow soon.

More information
Monitoring supplies
Great Lakes IPM - Traps & Lures
Gemplers - Traps

Blueberry maggot monitoring
Phytosanitary Requirements for the Importation From the Continental United States and for Domestic Movement of Commodities Regulated for Blueberry Maggot - Canadian Food Inspection Agency

Monitoring and management strategies for blueberry maggot - Michigan State University IPM Resources, Fruit Management Team Alert

Do you have a blueberry maggot problem? - Cornell University Cooperative Extension