Insects - Targeting the Prune Year Field for Blueberry Maggot Management
Prepared by Frank Drummond, Professor of Insect Ecology/Entomology, David Yarborough, Wild Blueberry Specialist. The University of Maine, Orono, ME 04469. February 2012.
A prune field management strategy for blueberry maggot fly has been researched and practiced in the maritimes for several years. This strategy has not been evaluated in Maine, although the University of Maine Cooperative Extension goal is to research this strategy over the next few years. This strategy has an excellent potential to eliminate or greatly reduce insecticide residues on wild blueberry fruit.
The ability to use this strategy for blueberry maggot management MAY be field specific. Ideally, for this strategy to work well a single split (half crop and half prune) ISOLATED field with little to no other sources of blueberry maggot fly nearby is BEST. This is because the underlying assumption is that MOST or a SIGNIFICANT proportion of the blueberry maggot flies attacking a crop field comes from the adjacent prune field which was crop in the previous year. This adjacent prune field is thus the MAIN source of attack and so if they can be killed BEFORE the move into the adjacent crop field then an insecticide application may not have to be made in the crop field.
This strategy requires :
- Fly trapping in BOTH the prune field and the crop field.
- The prune field should have traps placed well throughout the field
- The crop field should be trapped along the perimeter with a trap or two toward the field interior.
- Traps should be deployed EARLY before any fly emergence (about mid-June)
- As soon as the FIRST fly is caught in the prune field spray a persistent insecticide that has 5 to10 day persistence over the ENTIRE prune field.
- Continue to monitorthe traps at least twice a week.
- As long as flies continue to be caught in the prune field spray the field every 5 to 10 days.
- IF FLIES ARE CAUGHT IN THE CROP FIELD, the record their numbers and if the threshold for blueberry maggot is exceeded (6 or more for a single visit or a cumulative total of 10 flies / trap) then treat the perimeter (100 ft width) of the crop field.
- Continue to check traps in both fields and spray if necessary until harvest.
One observation from New Brunswick is that this Prune Management system is NOT ALWAYS consistently effective AND when it does work, it often requires spraying of BOTH prune and crop fields the first year of the strategy. However, we do believe that it may be worth it for some growers to try this out management approach. So long as the crop field is ALSO continually monitored, the risk of an unexpected infestation will be small.
See the illustrations below depicting the PRUNE FIELD STRATEGY
Improving this Prune Management System
One of the things that we want to research is if the perimeter strategy we currently use will work in the prune field as well as the crop field. Until we complete this research we recommend that the entire prune field be sprayed once a single fly is detected in the prune field. However, it might be that a 100 ft strip next to the crop field is all that is necessary, BUT we have do not know at this point whether this would have any efficacy in controlling the blueberry maggot.
Another focus of our research will be to determine if a threshold approach can be used in the prune field. So, INSTEAD of spraying when the first fly is caught, can we wait until 3, 5, or 10 flies per trap are caught in the prune field and then spray AND still prevent flies from colonizing the crop field.
However, UNTIL we can do the research to answer these questions we recommend that growers who trial the prune field method spray the ENTIRE Prune Field upon the FIRST capture of a blueberry fly.
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