The use of insect netting on existing bird netting support systems to exclude spotted-wing Drosophila from a mature small-scale commercial highbush blueberry planting

The use of insect netting on existing bird netting support systems to exclude spotted-wing Drosophila from a mature small-scale commercial highbush blueberry planting

Summary

Spotted Wing Drosophila (SWD) is an invasive fruit fly that threatens the viability of small scale, organic, and no spray berry farms throughout the U. S. SWD lays its’ eggs in fruit before it is fully ripe so control must be aimed at preventing egg laying. Because of this, IPM practices of using thresholds have been abandoned. One organically approved pesticide is effective against SWD and only two applications can be made before it must be rotated with other pesticides, none of which have been effective. Additionally, there are significant numbers of growers who do not want to spray. Small scale trials with insect netting showed promise for excluding this pest from plantings but there had not been any trials looking at systems that will allow a grower to cover their crop, yet still harvest efficiently, in comfortable conditions, without allowing SWD in during the process.

In July of 2014, Dale-Ila Riggs and Don Miles (owners) and their farm crew adapted their existing bird netting support system to cover 6 rows of blueberries with 80 gram insect netting, purchased from Tek-Knit industries, the manufacturer of the netting. At the request of Tek-Knit, one row of blueberries was covered with 60 gram netting, and one row was a control – covered with standard bird netting. The control row was sprayed for SWD, starting soon after the first capture of SWD in a trap in the blueberries. Starting July 15th, Laura McDermott, (technical advisor) collected blueberry samples every week, through September 15th. Nine sample sites in the 80 gram netting yielded 225 berries per week; 3 sample sites in the 60 gram treatment, and 3 sample sites in the control yielded 75 berries per week in each treatment. The berries were sent to Greg Loeb’s lab (technical advisor) in Geneva, where Steve Hesler put them in rearing cups and recorded how many adult SWD emerged from them over time. Results from this trial have already been shared with almost 400 growers at workshops/meetings in New York and Connecticut. Three more presentations will occur soon in New York and at the Mid-Atlantic meetings in Hershey PA.

Objectives/Performance Targets

In late-June 2014, my farm crew started to modify our existing bird netting support system of greenhouse hoops, moving them so that the hoops overlapped to create a V that greenhouse purlins that had netting attached could rest in the V. This was done over 6 rows of mature highbush blueberries. A separate support system made of upright pipes and horizontal purlins was constructed over one row of berries to hold the 60 gram netting. One row of hoops was left over the final row of berries to hold our standard bird netting. On July 9th, the 60 gram netting was placed over the support structure with pipes placed on the bottom to hold the netting in place. On July 10th, we replaced the 60 gram netting as it had blown off in a thunderstorm. This time we attached the netting to pipes placed on the bottom of the netting by wrapping the netting around the pipes and attaching it with plastic greenhouse clamps.
On July 11th we covered the 6 rows of blueberries with 80 gram netting. I had purchased 6 rolls of 13 foot wide netting. Pairs of rolls were sewn together so that we had 3 pieces of netting, 26 foot wide. We used standard greenhouse purlins, made of swedged tubing, connected to each other for the length of the 250 feet of row. The first 2 rolls of netting were joined by wrapping them around the continuous purlin, attaching the netting to the purlin with greenhouse clamps. The continuous purlin was slid up over the apex of the first set of hoops and placed in the V of the first two sets of overlapping hoops. The second piece of netting was pulled over the tops of the hoops in rows 3 and 4. To connect the second and third pieces of netting, we had to attach the next purlin to the upper side of one row of hoops. We did that using standard greenhouse connectors. We then attached pieces 2 and 3 to the purlin with the greenhouse clamps, and repeated the process of anchoring the edges on the ground to pipe.
Vestibules were built for us by a local carpenter and netting was attached to the vestibules by using standard wire lock channel and wiggle wire used in greenhouse construction. If the netting edges were not connected to the vestibules, we erected 4 x 4 posts at the seams, and connected the netting to the posts using the wiggle wire system.

Laura McDermott collected berry samples on a weekly basis. In the 80 gram netting she collected 25 berries in each of 9 zones, for a total of 225 berries per sampling. The 60 gram treatment and control each had three sampling zones of 25 berries/zone for a total of 75 berries per sampling. The berries were shipped overnight mail to Geneva. Steve Hesler, in Greg Loeb’s lab set the berries up in rearing cups and recorded how many berries eventually had SWD adults emerge from them. Laura also collected berries that she examined for oviposition scars and collected and examined contents from SWD traps on a weekly basis .

Accomplishments/Milestones

Records were kept to determine how long it took to modify our existing support system, to put up the netting, and any problems encountered. Infestation data was collected on a weekly basis.  Simply put, the project was a great success. During the 2 months that samples were collected, almost 2000 berries were collected from the 80 gram netting. Only 14 berries had SWD adults emerge from them – a .78% infestation rate. Three quarters of those berries were from one collection site – the site closest to the entry. They were collected approximately 2 weeks after my harvest crew had not properly closed up the vestibule while working.
This netting went through 3 severe thunderstorms and 2 hail storms. It was still in great condition at the end of the trial when we took it down in late October. We learned a lot from our process of putting it up and we are going to modify our system next year to make it even easier to use.

Impacts and Contributions/Outcomes

We held a field day at the farm in mid-August so that growers could view the netting and discuss SWD management options. Approximately 30 growers attended plus Extension staff. The owner of the manufacturing company drove from Montreal to attend the meeting as well. We discussed needs of the industry to make the use of large scale netting coverage even more user friendly. One of those is zippered panels to make it easy for people to come and go and properly close the netting. Another is a “repair kit” for potential damage, and the third is price. The manufacturer has promised to look into finding a supplier to provide panels with tent zippers in them for easy entry/exit. They say they will also look into finding adhesives that can be used in a repair kit. Lastly, they asked me to become their Eastern U.S. distributor (which I have agreed to do). As a grower, working with them, I believe we will be able to make the product even more user friendly for large scale commercial use. And I have some ideas on how to bring the cost down to growers by working with other agencies.

I presented preliminary results of this trial at the Northeast SWD working group in mid-September and as of mid-january, I have presented the results from this trial at 2 SWD workshops held in NYS and at the CT Fruit and Vegetable Conference. So far, I have reached about 400 growers and Extension staff through these meetings. I am also speaking about this project at the NYS Produce Expo, the mid-Atlantic Fruit and Vegetable Conference in Hershey PA, and one more SWD workshop in Western NY in early March. I sent Vern Grubinger photos of the vestibules and covered planting for him to use at the VT Vegetable and Berry Growers meeting on January 20th. I have already had growers contact me about erecting netting over their plantings, and American Agriculturist is interested in doing an article about the project.

In 2012, I lost 40% of my blueberries to SWD – a $6200 loss. In 2014, I lost no berries from under the 80 gram netting. I believe that when word gets out about the success of this project, many more growers will be interested in adopting this technology, especially if I am successful in setting up a cost-share program.

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