Evaluation of exclusion and mass trapping as cultural controls of spotted-wing Drosophila in organic blueberry production

Evaluation of exclusion and mass trapping as cultural controls of spotted-wing Drosophila in organic blueberry production

Summary

Spotted Wing Drosophila (SWD) is an invasive fruit fly that proved to be unusually damaging to 2012 berry crops. Unlike native species, SWD uses its formidable ovipositor to deposit eggs in ripening fruit resulting in larvae development inside the berry that corresponds to the ripening of blueberries, raspberries, day neutral strawberries and a variety of other cultivated and wild hosts.

This field trial examined 1.00mm x .85mm Dubois Agrinovation Protek insect netting as a means of exclusion. We evaluated exclusion alone and in combination with two different types of traps – unbaited red sticky ball traps (similar to traps used for apple maggot control in organic orchards) and yeast-baited traps.

Generally, we are encouraged that the netting did not affect the quality or yield of the berries. Light and temperature differences did not seem to be significant. We were mostly pleased with our netting design for the purpose of a study, and will elaborate on suggestions for change in the final report.

Objectives/Performance Targets

This field trial examined 1.00mm x .85mm Dubois Agrinovation Protek insect netting as a means of exclusion. We evaluated exclusion alone and in combination with two different types of traps – unbaited red sticky ball traps (similar to traps used for apple maggot control in organic orchards) and yeast-baited traps.

 The ProtekNet insect netting is 80% porous and has 83% light transmission capabilities. The suggested life of the net is 1-3 seasons but anecdotally and if stored well it may last several additional seasons. The net was hung over 1 row of 50 plants that is intersected midway with an aisle for a total of 300 linear feet. To separate the treatment replications within this row we used extra netting material fastened with pig rings. The intent was to provide SWD exclusion between treatments while still allowing air movement and light penetration. This separation feature is less important from an overall exclusion strategy as it is unlikely to be replicated in commercial fields. Light measurements were taken twice in the control and under the netting.

 The timing for applying the netting, after bloom and before berries begin to turn color, was intended to aid in preventing early infestation in the netted treatments. The exclusion netting was hung over wires placed at a height of 6’ to accommodate pickers. The wires, anchored to 2 H-braces at rows’ ends were supported by posts set strategically along the row.

 There were four treatments plus the control. Three plants per replication were netted and each treatment was replicated 3 times. Treatment 1 was the thrips netting alone; Treatment 2 was thrips netting and unbaited red sticky ball traps; Treatment 3 was thrips netting and yeast/vinegar baited traps. The controls, also three plant replications, had no netting or traps.  

Treatment 4 (not included in the original design) consisted of four sections of three plants all of which had Lumite 994GC woven fabric ground cover made of UV stabilized polypropylene, a material which is designed to allow passage of water, nutrients and air while suppressing weeds. One section was matted with no netting, the other three sections were netted, one with no trap, one with an unbaited red sticky ball trap, and one with a baited yeast/vinegar trap.

Berries from the entire row were hand harvested two times a week for three weeks. Data was collected from the center plant in each replication. New traps were hung weekly.

 The plants were treated consistently and were all the same age (5 years) and mid-season variety (Blue Crop). Sprays were not used. All other cultural inputs were identical across all 3 treatments and the control – this included weed and disease control, fertilization, and irrigation. (We did not require frost control).

Accomplishments/Milestones

The weather cooperated and we were able to complete the mechanics and the data collection of the project as planned. The SWD did not “cooperate” for study purposes, because SWD did not show up as early as expected. We found only minor trappings of this species of drosophila in our field until the middle of August, when the study period ended and the berries were effectively picked-out. During the time of our study, we identified only a few SWD trapped in the controls (none in the netted traps or harvests). We collected general observational data on native fruit flies and other insects trapped in the study which we will analyze further in the final report. We also collected light and temperature differences with and without netting, as well as data on fruit size, yield, appearance and quality.

Impacts and Contributions/Outcomes

Generally, we are encouraged that the netting did not affect the quality or yield of the berries. Light and temperature differences did not seem to be significant. We were mostly pleased with our netting design for the purpose of a study, and will elaborate on suggestions for change in the final report.

Three reasons for adding the matted treatments relate to currently known information about SWD. SWD tend to find cover in shaded and weedy spaces near their hosts during the heat of the day. The dark color of the matt heats up faster than the ground in the sun and it cuts down significantly on weeds (a major issue for organic growers). In addition, clean up of dropped fruit is quite easy on the matt, because the fruit was easy to find and sweep up with a broom.  The use of weed fabric could be helpful in discouraging insects from sheltering nearby and in removing potential larvae from the field. Matting might be useful to study.

About SWD: We are not sure that SWD will always arrive in mid-August in our area, but our currently-productive plantings are early- to mid-season varieties.   In 2015, eight rows of late-season Nelson and Elliott varieties will come into production. By that time we will consider using netting in that section. The decision will be based on more information about the insect overwintering patterns, further analysis of our data as well as other regional data, and the possibility of using other strategies (organic fungal, bacterial or cultural controls) that target SWD without threatening the sustainability and health of our land.

In early January I am sitting down with my technical advisor Laura McDermott to complete data analysis and work on the final report for this study which we will plan on submitting in late February 2014.

Collaborators: