Management of the Spotted Wing Drosophila using High Tunnels

Project Overview

Project Type: Farmer/Rancher
Funds awarded in 2014: $14,850.00
Projected End Date: 12/31/2015
Region: North Central
State: Minnesota
Project Coordinator:
Erik Gundacker
Scenic Valley Farm

Annual Reports

Information Products


  • Fruits: berries (other), peaches


  • Pest Management: physical control, prevention, sanitation, traps

    Proposal summary:

    Project Description
    We will research methods to manage and control infestation of spotted wing drosophila (SWD) that is negatively impacting strawberry, raspberry, blackberry and other fruit farms in the North Central region. The research will focus on using high tunnels and insect netting to prevent rapid population build up of the SWD.

    Description of farm or ranch and project coordinator background
    Erik Gundacker is the co-owner of Scenic Valley Farms located in Rosemount, MN and Readstown, WI. Scenic Valley Farms manages ten high tunnels that produce certified organic blackberries, strawberries, raspberries, tomatoes, peppers, cucumbers, eggplants, melons, spinach and various other produce. SVF markets the produce to coops, wholesale brokers, and restaurants in the Minneapolis, Chicago and Milwaukee areas. The high tunnel management practices of the company naturally increase soil fertility through the addition of compost, greensand, and rock powders. We also reduce soil erosion by incorporating natural and synthetic mulches.

    Below is a short description of some of the grant projects that SVF has administered related to high tunnel agriculture:

    • Minnesota Sustainable Agriculture Demonstration, Wisconsin Agricultural Development and Diversification and SARE grants to research and evaluate the feasibility of overwintering thornless variety blackberries using high tunnels in a zone 4 hardiness zone. With the assistance of these state and federal grant funds, we have successfully developed thornless blackberry production in the Upper Midwest and shared the methods and practices with other growers. As a result of our efforts, several growers in the region are now imitating our practices and we have been discussing forming a consortium of blackberry growers to distribute the produce.
      • Phase I and Phase II USDA Small Business Innovation Research to develop an environmental control system that monitors and manages soil temperature, air temperature, and soil conditions within high tunnels. The interface consists of a fully integrated, user-friendly color touchscreen. The user can also interface with the controller through any internet connected device such as a laptop, smartphone, or tablet. The control system under development also manages soil and air temperatures through the use of solar thermal heating. Fans collect air heated in solar panels and move it through tubing embedded in a thermal mass which increases both soil and air temperatures within the high tunnels.
      • A USDA Value Added Producer Grant to develop a marketing and distribution plan for a line of organic blackberry value-added products. These include personal care and medicinal products.

    Jesse Downs is the co-owner of Down Home Farms which is located in Reads town, WI. Jesse’s farm grows garlic, onions, squash, strawberries, raspberries, and various other certified organic produce. Jesse has also pioneered the production of high tunnel grown organic peaches in the region, using the technology to successfully overwinter the crop. Down Home Farms specializes in retailing its produce at local farmers markets and restaurants.

    Connie King is the co-owner of Prairie Belle Enterprise which is located in Dewitt, IA. They produce organically certified blackberries, tomatoes, peppers, and other fruits and vegetables in high tunnels. Prairie Belle Enterprise markets in local farmers markets and restaurants.

    The spotted wing drosophila (SWD) is an invasive vinegar fly which lays its eggs in immature and ripe fruit; thus its larvae may be present in otherwise marketable fruit. Tiny white maggots in just-picked berries may be the first noticeable sign of a SWD infestation. This new menace to late summer and fall fruit crops throughout North America can cause severe losses to commercial growers. According to Kathy Demchak, a Penn State University horticulturist, raspberries, blackberries, and blueberries produced in mid-summer or later have been affected to
    the greatest extent, but SWD can also affect cherries, plums, peaches, and grapes or any other soft thin-skinned fruit. Native to Southeast Asia, the SWD appeared in California in 2008. Within 3 years, it had arrived in Florida, Michigan, Oregon and other states. In 2012 the SWD was discovered in several counties in Minnesota and Wisconsin. In 2013, a University of Wisconsin, Madison monitoring program discovered the pest on all 24 of the farms included in the survey. Many of these farms suffered severe economic losses because of the infestation
    and some of the growers are considering abandoning berry production altogether.

    Using a saw like ovipositor, the female SWD lays eggs in ripening fruit. Tissue surrounding egg-laying sites begins to discolor and decay within a few days. Larvae hatch from the eggs, growing up to 1/10th inch long as they burrow and feed inside the fruit. The fly moves freely on infested fruit. Cold weather slows its spread, but as temperatures return to the 70s, populations explode with eight to nine generations a year.
    • Unlike other fruit flies, SWD attacks ripening fruit
    • Difficult to control with pesticides once larvae appears in fruit
    • Short life cycle and overlapping generations make spray timing difficult
    • Requires sprays near harvest time
    • Requires multiple sprays which can lead to pesticide resistance
    • Infestation has resulted in a single season destruction of entire field
    • Because is it already widely distributed in the US, there is no internal quarantine on this insect
    • Crop loss in eastern US due to SWD, $48M - $55M (2012)

    Cultural strategies such as picking ripe fruits daily and removing culls and overripe fruits without composting them are the current recommended control. These cultural practices will eliminate some of the SWD but inevitably the small white larvae will appear in fruit on supermarket shelves and farmer’s markets tables. In order to properly manage the pest on even small farms such as our own, additional controls need to be explored.

    Our proposed solution is to develop procedures that attempt to prevent as many SWD as possible from entering the high tunnels (Objective 1) and effectively control them using organic methods once they have entered the growing structures (Objective 2). In order to prevent population build up, we will install fine mesh insect screen across the side walls and any other openings of the tunnel. We believe this solution will prevent sizeable numbers of the pest from entering the high tunnels. The remaining population, which will be much easier to manage due to its low numbers, will be managed through the application of organically approved insecticides.

    Care will be taken to ensure that the pollinators within the tunnels have been returned to their hives before any applications are delivered.

    Prairie Belle and Down Home Farms will grow blackberries and peaches in a single tunnel each. Scenic Valley Farms will have one tunnel in blackberries, one in strawberries, and one in raspberries. The following timeline applies to all tunnels on all farms.
    1. May 1, 2014. Set four traps (plastic containers containing apple cider vinegar) around outside of high tunnel. This will determine if any survived the winter
    2. Check traps daily for male and female SWD. Record the findings.
    3. June 1, 2014. Install 80 gr insect screen over side walls, service doors, and other openings on the high tunnels. In order to counteract the air flow restriction that will result, we will install a single exhaust fan or remove plastic from one end wall and replace with insect screen.
    4. June 1, 2014. Set four traps containing the apple cider vinegar solution inside each tunnel
    5. If SWD are detected in the inside traps, apply ORMI approved Entrust in the early evening according to the label once the pollinator hives have been removed from the tunnels (We anticipate that the screen will act as a barrier for more than 95 percent of the SWD)
    6. Return pollinator hives to the tunnel early the next morning
    7. Place 5 additional traps within the tunnel to assist in controlling the population
    8. To the extent possible, remove all culled and overripe fruit from tunnels
    9. Check traps daily inside the tunnel.
    10. If more SWD are detected in the traps, apply Entrust a second time
    11. Continue to monitor traps.
    12. Alternate Entrust applications with Pyganic (also an OMRI approved insecticide) in order to prevent resistance buildup

    • Create a page on the Scenic Valley Farms’ website that contains a general overview of the project
    • Host a field day in early September during both years of the project. The field day will be advertised and promoted on the University of Minnesota SustAg List Serv, the Center for Integrated Agricultural Systems at the University of Wisconsin, both the Midwest Organic Services Association (MOSA) and the Midwest Organic and Sustainable Education Service, the Beginning Farmers website, the Viroqua Cooperative, local extension services and other organizations
    • Create a three-fold brochure that provides details on the project
    • Provide brochures and project status presentations to the Wisconsin Berry Growers Association and the Minnesota Fruit and Vegetable Growers Association and Minnesota and Wisconsin high tunnel conferences (which have more than 2000 attendees).
    • Build a web blog with a detailed narrative and images of the project
    • Produce a three-fold brochure of project information and pass out at various functions
    • Hold an open house at the end of each summer. Advertise with the local extension service and the various agricultural associations.

    Previous Research
    Kathy Demchak at Penn State University has conducted research on using cultural practices to manage SWD populations. The practices she researched included daily harvests, removing overripe fruit, and disposing of culls through burying or burning (composting the berries proved ineffectual because the flies continued to breed). She indicated that these methods were somewhat effective but were conducted on a very small scale and are simply not practical for a larger working farm. At Scenic Valley Farms we determined that a daily picking regimen was
    not feasible due to others tasks that needed to be completed and the need to take a day off from work. However, we also discovered that missing a daily picking can cause populations of the SWD to increase quickly. We also found that it is largely impossible to pick all ripe and over ripe fruit off the ground.

    Other research has been done on removing nearby wild hosts, including wild raspberries and blackberries, cherries, mulberries, dogwoods, viburnums, and even pokeweed. SWD thrives in dense foliage with high humidity and moderate temperatures.

    According to Demchak, SWD numbers are reduced substantially during winters in northern states. That is probably why early season strawberries such as day-neutrals and June berries have minimal infection. She has authored a 4-part series of fact sheets on SWD including information on pesticides that can currently be used, and the series is now available online:

    • Spotted Wing Drosophila, Part 1: Overview and Identification [Pub. No. EE0042]
    • Spotted Wing Drosophila, Part 2: Natural History [Pub. No. EE0043]
    • Spotted Wing Drosophila, Part 3: Monitoring [Pub. No. EE0044]
    • Spotted Wing Drosophila, Part 4: Management [Pub. No. EE0045]

    Several previous SARE grants involved research relative to the SWD. None involved using a combination of high tunnels, insect netting, and OMRI approved insecticides to control SWD. The closet was project FNE13-784, Evaluation of Exclusion and Mass Trapping as Cultural Control of SWD in Organic Blueberry Production. It involved covering blueberries grown outside with an insect net. For this project the net was hung over 1 row of 50 plants and intersected midway with an aisle for a total of 300 linear feet.

    More generally, Scenic Valley Farms has already done work on using high tunnels to overwinter and increase production of high tunnel grown blackberries in a hardiness zone 4. The project, partially funded by a previous SARE Farmer/Rancher grant, provided convincing evidence that by utilizing either solar thermal or small amounts of propane heating, thornless floricane blackberries can be overwintered in the Upper Midwest

    The primary objective of the project is to eliminate SWD infestations of berry and other fruit crops using insect netting on all openings of a high tunnel with minimal or no use of insecticides. The project involves five high tunnels at three different farms in three different states producing berries and peaches from June to November.

    In order to determine if the primary objective is successful the participants will count SWD found in the traps both inside and outside the high tunnels during the growing season. Using data collection worksheets designed by SVF, the participants will record initial and ending harvest dates, and weekly quantities of marketable and unmarketable fruit. They will also record the number of SWD found in each trap on a weekly basis and the labor requirements to collect the traps and examine for pests. Any visual sightings of the SWD outside of the traps will also be recorded. Additionally, on a weekly basis, we will visually inspect an agreed upon weight of harvested fruit for any indications of larvae within. We will then be able to approximate the percentage of fruit within the high tunnel that is infected with larvae and therefore not marketable. Each insecticide application date will also be recorded so the impact of the spraying can be determined.

    The data will be recorded throughout the growing season. We will then have a complete record of when the SWD first appear in the traps and whether or not the physical barriers are proving successful.

    We will record all expenses for control of the SWD including man hours dedicated to installing the netting and spraying insecticide.

    In order to analyze the SWD count we will make a series of charts comparing SWD counts from traps inside and outside the tunnels for each variety of fruit. We suspect the results will show that the SWD is not totally eliminated by the netting but at most, one or two applications of the insecticide will be needed, and that minimal quantities of fruit will be unmarketable because of the presence of larvae. The expectation is that the results of the project, along with outreach efforts, will encourage even more local growers to adopt high tunnels modified with the
    physical barrier of insect screen. SVF will be primarily responsible for ensuring that the data is collected on a regular schedule and will also compile the data for analysis.

    The fruit will be grown and processed according to strict organic standards. Any culled or unmarketable fruit will be buried at least one foot below ground on the day of the harvest in order to prevent breeding from occurring outside the high tunnels.


    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.