Management of the Spotted Wing Drosophila using High Tunnels

2014 Annual Report for FNC14-948

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

Management of the Spotted Wing Drosophila using High Tunnels


The work related to the grant funds mainly related to three activities:
(1) monitoring the presence of the Spotted Wing Drosophila (SWD),
(2) installing insect netting on the high tunnel greenhouses as well as placing the same type of netting on field grown strawberry crops, and
(3) applying organically approved insecticides once the SWD were detected.
The unusually harsh winter of 2013 – 2014 disrupted our research activities. The varieties of
blackberry canes grown in the high tunnels of Scenic Valley Farms (SVF) and Prairie Belle
Enterprises must be overwintered in order to allow the primocanes to produce fruit the following  year as floricanes. The varieties (Natchez, Ouchita, Apache, were developed by a breeder in Arkansas and sustain damage to their canes if temperatures drop below -12° C (10F). Because  of the amount of LP required to sustain a minimum temp of 10F we decided to set the minimum  of 0F. This temp has worked for the last 6 years with no noticeable damage to the canes. We had installed 170,000 BTU thermostatically controlled tube heaters in the blackberry high tunnels.

We had major cane damage during last winter’s brutal weather. We surmised the reason for the cane loss is: According to the temp records there were 50 days at which the temps fell to 0F or colder. According to John Clark, U of Ark the breeder for the above blackberry varieties, the berries are supposed to be good to 10F. He said 50 days of below zero with many consecutive days was the problem. He said 5F setting for a minimum temp should do better. For the winter of 2014/2015 we are setting our thermostats to come on when the temp falls to 5F.

Prairie Belle Enterprises made the decision in early May to remove the floricanes and allow the primocanes the advantage of more exposure to sunlight and more access to soil nutrients. Connie King made this decision reluctantly, but felt she had no choice due to the brittle nature of the floricanes and the almost complete lack of flower bud development.

SVF also noticed severe damage to the floricanes and minimal flower bud development at about the same time. We decided to remove approximately 90 percent of all the floricanes with the hope that the remaining 10 percent might produce enough blackberries to conduct research on and for our own personal consumption.

Fortunately, the extreme cold weather did not appear to damage the crowns of the blackberry plants. In fact, due to the lack of competition from the floricanes, the primocanes flourished during the 2014 growing season and assuming no heater malfunctions or extreme cold weather in the upcoming winter, and with the minimum heater controlled temp set a 5F, both farms expect to have a healthy harvest next year.

On his farm, Jesse Downs grows peaches in his high tunnel. He covered his tunnel with netting, set inside and outside traps and reported no SWD inside the tunnel...Of course we do not know for sure if peaches attract SWD.

At both farms, we spent a considerable amount of time installing the insect netting on the high tunnels. What we anticipated would be a fairly straightforward, simple job turned out to be anything but that. The problem is that high tunnels are not designed to prevent extremely small insects like the SWD from entering. On the blackberry high tunnels, we also removed the plastic from the end walls to allow for better airflow during the warm summer months. So we needed to design a system that would be both effective as a blockade against the SWD and versatile enough to be used in subsequent years.

We elected to use insect netting manufactured by ProtekNet. The dimensions of each roll of
netting is 13’ X 328’. The mesh is 1.00 mm X .60 mm. This size opening was chosen because it was small enough to prevent SWD from entering but large enough to only restrict approximately 20 percent of natural airflow.

We secured the insect netting to the side walls with a combination of uchannel/wiggle wire and wood lathe. We first removed the wiggle wire from the uchannel on the hipboard that held up the plastic on the roll up and down sidewalls. We then attached the insect netting and reattached the sidewall plastic with the same lengths of wiggle wire. Using self-tapping screws, we attached uchannel to the corner bows on the sidewalls and then secured the insect netting to these lengths of uchannel. On the sidewall baseboard, we pulled the insect netting tight, and then used four foot lengths of wood lathe and .5” wood screws to secure the netting to the baseboard. This method sealed up the sidewalls tightly.
The end walls and especially the doors presented more of a challenge. We removed the poly
from the end walls and using two lengths of insect netting, secured it using the existing wiggle
wire. We then reattached the end wall plastic over the netting using a second set of wiggle wire in the same unchannel. Along the ground, openings were closed using ground stakes spaced roughly one foot apart. A similar method was used on the doors. To block openings along the door headers and jams, we folded the netting and stapled the edge to the door frame to create a “seal”. This didn’t completely seal up the doors but all along we knew that it was impossible to prevent all SWD from entering the tunnels.

Sealing the tunnels in this manner prevented pollinators from entering the tunnels but fortunately both farms use bumblebee hives within the structures. We slightly opened a valve at the end of an irrigation drip line so that the bees would have access to water since they wouldn’t be able to leave the tunnels.

We also installed a 6000 CFM thermostatically controlled exhaust fan in two strawberry tunnels to increase airflow since the netting would cause temperatures to be higher than normal during the summer months.

At SVF, we enclosed five tunnels using the methods described above: two blackberry tunnels,
two tunnels of June-bearing strawberries, and a tunnel of day neutral strawberries. At Connie
Kings’ farm, a single blackberry tunnel was enclosed. At Jesses Down’s farm a single peach
tunnel was enclosed.

In each tunnel we placed four SWD traps evenly spaced throughout the growing area. The traps consisted of plastic containers with sealable covers and small perforations to allow the flies to enter. Half of the traps contained a vineagar mixture and the other traps were mixture of sugar dissolved in water. In each trap, we placed a drop of dish soap to prevent the flies from leaving the traps.

We also placed traps outside to compare the SWD population with those present inside the
tunnels. The traps were placed along the edge of the woods bordering the fields and next to a
row of strawberries planted outside (described below).

Although not described in the original grant proposal, we also conducted research on growing
strawberries in an outdoor field environment. In early May, we planted day neutral strawberries in a 100-foot-long raised bed. The berries were then covered later in the summer using row cover hoops and insect netting and the netting was attached to the hoops using clothespins.

The results of our research look promising but it will require another growing season to confirm those results. As expected, the remaining floricanes in the SVF high tunnels produced minimal fruit although we harvested 75#s of blackberries from the Rosemount tunnel. The traps within the Readstown tunnel showed no presence of the SWD until late-July and the population was very small with just a few insects in the trap nearest the fruiting canes. At this point, we collected the bumblebees and removed the hive in the evening. We then applied Entrust SC Naturalyte at the rate specified in the label and returned the hive to the tunnel the next morning. The berries only continued to fruit for another week and showed no signs of SWD infestation. In the Rosemount blackberry tunnel that we harvested 75#s of blackberries, we covered with netting, set traps and had no indication of SWD. The previous year we had SWD in this tunnel. The real test will be this coming growing season, when we expect a healthy crop of blackberries in both tunnels.
The traps placed in the tunnels of June-bearing strawberries showed no presence of the SWD. But this was hardly surprising considering that we finished harvesting that crop in early June and the SWD does not typically begin to appear in southwest Wisconsin until July at the earliest.

The tunnel that had the highest level of infestation was the tunnel planted in day neutral
strawberries. This is primarily because day neutral varieties bear fruit throughout the summer and fall months, and the SWD population peaks in August. For several days in August, the doors to the day neutral tunnel were accidentally left open. Shortly afterwards, we began to notice larvae in the fruit and increased counts of both male and female SWD in the traps. At that point, we expected to have a major challenge on our hands to control the population and prevent significant damage to the fruit. This did not turn out to be the case however. We applied Pyganic Crop Protection EC 5.0 II for three consecutive days because it is a contact insecticide. We then applied Entrust, waited a week, and then applied Entrust again. The most challenging part of this treatment program was making sure that we removed the bumblebee hive from within the tunnel and then reintroduced the hive after a safe interval. After two weeks, signs of adult SWD in the traps all but disappeared and the fruit showed minimal damage. During this period, and for the remainder of the growing season, we were careful to instruct the harvesters to remove any overripe berries on the plant or berries lying on the ground. These berries were then buried at a depth of approximately two feet.

In our opinion, the primary reason we were able to control the SWD outbreak in this tunnel is
because of the insect netting. It largely prevented new adults from entering the tunnel while we were attempting to control the population already in the tunnel. Without this protective barrier, we would have been forced to apply insecticide throughout the entire harvest season which would have resulted in much higher labor and material costs and a less healthy crop of berries. During the period of infestation, we were forced to cull approximately 30 – 35 percent of the harvest but these figures dropped back to their more typical 10 – 15 percent range once the infestation was brought under control.

The day neutral strawberries growing in the outdoor field environment were uncovered until late summer and as a result the fruit became heavily infested with SWD larvae and was completely unmarketable. Once the hoops and netting were in place, we applied Pyganic Crop Protection EC 5.0 II directly through the netting for three consecutive days and then switched to a single application of Entrust. We followed this six days later with another application of Entrust. By the third week there was almost no indication of SWD and we were able to continue marketing the fruit. In order to harvest the berries, we removed the netting and then reattached it afterwards with the clothespins. The key again seemed to be the insect netting.

All the traps outside indicated the presence of both male and female adult SWD. The insects
were first recorded in the traps in late July. The number of SWD in the traps peaked in mid-
August and they largely disappeared by early September. As anticipated, the trap with the
highest recorded number of adult SWD was located near a stand of wild blackberries. Growers attempting to control the SWD population on their farms might thus consider removing wild stands of berries located near their fields. Last growing season was unusually cold and wet throughout May and June, and we expect this might have delayed the onset of the SWD. In previous years, signs of the SWD began to appear in early July.

On a side note, growing raspberries outside, Jesse Downs used cultural methods to try to control SWD infestation in his raspberry patch. Because his cultural practices were failing he reduced the size of his raspberry patch by 50% to better manage.

The major focus for the next year will be on prevention and monitoring. The laborious task of
installing the insect netting was completed in the first year of the project and this will allow us to focus our energy on data collection and population control.

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. Set four traps within each tunnel as well.
2. Check traps bi-weekly for male and female SWD. Record the findings.
3. If SWD are detected in the inside traps, use no more than three applications of Pyganic followed by one application of Entrust.
4. Return pollinator hives to the tunnel early the next morning
5. Place 5 additional traps within the tunnel to assist in controlling the population
6. To the extent possible, remove all culled and overripe fruit from tunnels
7. Check traps daily inside the tunnel.
8. If more SWD are detected in the traps, apply Entrust a second time
9. Continue to monitor traps.
10. Alternate Entrust applications with Pyganic (also an OMRI approved insecticide) in order to prevent resistance buildup
11. Investigate a better insect net mending tape. Netting sometimes gets damaged due to rabbits girdling, animals inside the netted tunnel attempting to escape, human tools, etc. We tried high tunnel poly mending tape, mending tape supplied by the netting manufacture with no success. We plan to approach 3M to see if they have anything that will work.
12. We plan to continue our work with controlling SWD on outside strawberries covered with
netting. We plan to analyze pollination on strawberry rows covered with netting.

We will record initial and ending harvest dates, and weekly quantities of marketable and
unmarketable fruit. Each insecticide application date will also be recorded so the impact of the spraying can be determined.
Labor costs will also be recorded but we do not expect them to be much different in the coming season compared to the last season. Typically, it required approximately one hour for a single person to prepare the sprayer and apply the insecticide for a single high tunnel. Additionally, we estimated that removing overripe and rotten fruit while harvesting increased the harvest time by around 10 percent but such practices should be undertaken on a regular basis anyways.
We hosted an open house in September that was attended by more than forty individuals. The open house was not solely intended to disseminate information about our efforts to control SWD, but most of the growers present were uniquely interested in our research.

At the upcoming MOSES Organic Farming Conference, Erik Gundacker will be delivering
information on several aspects of our farming operation including our SWD control efforts. Erik will also most likely be presenting at the annual Minnesota High Tunnel Conference.

We will also create a page on our website that provides a summary of our control efforts along with photos and descriptions of how we installed the insect netting on the high tunnels as well as out in the field.

Objectives/Performance Targets


Impacts and Contributions/Outcomes