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

View the project final report

• 2013 annual report

Commodities

• Fruits: berries (blueberries)

Practices

• Pest Management: cultural control, field monitoring/scouting, physical control, row covers (for pests), traps

Spotted Wing Drosophila (SWD) is an invasive fruit fly of Asian origin first detected in the Pacific Northwest in 2008. Since then it has rapidly expanded its range to include much of the continental US and many provinces in Canada. On my farm, SWD likely caused a 30% loss of my blueberry crop during this first season of infestation; extension reports indicate that many growers abandoned or even removed their fall raspberries as a result of this pest. Blackberries are also prime targets. SWD management is exceptionally challenging for organic berry growers, as existing recommendations involve extremely short spray rotations (3-7 days) with Entrust and Pyganic. Anecdotal information indicates that Pyganic is so ineffective that growers feel they lose ground when using it, yet a pesticide rotation is mandated to keep within the label requirements, and the rotation strategy is important as it helps prevent pest resistance. For many small berry growers, reliance on 100% chemical control is unsustainable. I have built my business on an organic production model and my customers place a high value on that. I truly believe that this pest, if left unchecked, will cause irreparable harm to my farm business. In an effort to be proactive, I would like to explore the combined approach of exclusion and trapping to reduce the number of SWD adults in my small organic blueberry planting. Through discussion with my cooperative extension agent and searching information on the web I have found that this approach has not been extensively explored in other areas of the country likely because large acreage farms would find it prohibitively expensive. There is one home gardener fact sheet written by the University of Oregon Cooperative Extension that suggests using exclusion as a way to control SWD in small plantings. Encouragingly first hand reports from Japan indicate that exclusion is a valuable control strategy for Japanese berry growers. I feel that on a small scale, exclusion and trapping would allow growers to reduce the amount of pesticides sprayed and still grow a high quality product. My approach will be to examine exclusion by itself, and combined with baited traps in comparison to a control. The importance of this work may only be temporary, as the long term solution to this pest seems likely to hinge on some type of mating disruption or introduction of a predator. The real value to the work will be to provide small, sustainable berry growers with a reasonable cultural control method that actually works. This approach may give growers enough encouragement that they will continue attempts to manage the pest and hopefully not interrupt the supply of locally grown berries for northeastern customers. Even temporary loss of the market would be difficult to regain. 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. Levels of infestation ranged from 80-100% of fruit examined. Individual fruit had as many as 25 larvae; coastal farms were reported to have more than 3000 adults trapped in a 1-week interval. Traditional IPM approaches have been temporarily abandoned in hopes of controlling SWD populations. Insecticide applications at 3-7 day intervals are currently the recommended strategy. Many berry growers are not inclined nor prepared to use insecticides and their customers are particularly concerned about food safety. It is imperative that an effective cultural approach be developed to allow sustainable and organic berry production to continue. This project will evaluate the merits and costs of excluding SWD from a blueberry planting using insect netting. We will also examine the effect of exclusion used in conjunction with baited lures designed to trap out the adult insect. Hay Berry Farm LLC is uniquely suited to this work as we are attempting organic certification and have invested heavily in bird netting, trickle irrigation and deer fencing. Additionally the farm enjoys strong support from our Cornell Cooperative Extension agent, who will assist in evaluating fruit, assembling the nets and hosting a field meeting.

This field trial will examine .35mmx.35mm Dubois Agrinovation Protek thrips netting as a means of exclusion. Additionally we will evaluate 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 secondly yeast baited traps.

The netting we will use is Proteknet Ultimate Plus Insect Netting, which has a 0.35mm x 0.35mm mesh, sufficiently small to prevent insect entry. It is 62% porous and has 89% 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 will be 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 will use row cover and Velcro. The intent is to provide SWD exclusion between treatments as best we can, while still allowing air movement and light penetration. This will be important for evaluating the treatments but is less important from an overall exclusion strategy as it is unlikely to be replicated in commercial fields. Light measurements will be taken weekly in the control and under the netting. Temperature measurements will be taken daily in the control and under the netting.

Netting will be applied after bloom is finished but before berries begin to turn color. This should aid in preventing early infestation in the netted treatments. The exclusion netting will hung over 2 wires placed at a height of 6’ to accommodate pickers. The wires will be anchored to 2 H-braces at either end. The wires will be supported by 6 posts set strategically along the row.

There are four treatments including the control. Four plants per replication will be netted and each treatment will be replicated 3 times. Treatment 1 would be the thrips netting alone; Treatment 2 would be thrips netting and red sticky ball traps; Treatment 3 would be thrips netting and yeast traps. The control will have no netting or traps. Data collection will be from the center two plants in each replication. They will be hand harvested 2 times each week for 3 weeks.

Three sticky apple maggot sphere traps that are unbaited will be hung in each replication of that treatment. Two yeast-baited traps will be hung in each replication of that treatment. The traps will be gathered weekly and data collected from them. New traps will be hung weekly.

The plants will be treated consistently and will be all the same mid-season variety. Sprays will not be used unless flies are present in such high numbers that they threaten the rest of the planting. If sprays are called for, all treatments will be organically approved. Spray records will be kept.

All other cultural inputs will be identical across all 3 treatments and the control – this includes weed and disease control, fertilization, irrigation and frost control. Locating the treatments within one area allows me to use row cover to help prevent frost in the treatment and control blocks. I do not normally cover the planting in the event of frost, nor am I able to overhead irrigate. In the event of a devastating frost I would need to ask for an extension of this project.