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
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 2015, based on observations and ideas gleaned from our 2014 trial we modified our netting attachment system. Based on our 2014 experience, we also tested only 80 gram netting in comparison with a control row. We re-used the netting that we had purchased from Tek-Knit industries in Montreal Canada, the manufacturer of the netting. Once again, the control row was sprayed for SWD, starting soon after the first capture of SWD in a trap in the blueberries. Starting July 16th, Laura McDermott, (technical advisor) collected blueberry samples every week, through September 2nd. Nine sample sites in the 80 gram netting yielded 225 berries per week; 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 the 2015 trial were shared with growers and Extension staff from throughout the Northeast at a field day at the farm on September 2nd. The results from the 2014 trial were shared with over 600 growers at workshops/meetings in New York, Connecticut, and Pennsylvania. I am also on the program for sharing the results in Massachuetts on February 6 2016. An article about the project appeared in the Fruit Grower News in May 2015. This is a publication based in Michigan that is distributed nationwide. The article can still be found on-line on their web site.
Based on our 2014 experiences, we decided to try simplifying and strengthening our attachment system. Rather than wrapping netting around the purlins and using plastic greenhouse clamps to secure it, we purchased wiggle wire channels that we attached to the purlins, and then used standard wiggle wire (used in practically all greenhouse attachment systems) to attach the netting to the purlins. We also attached the purlins directly to the hoops that supported the netting, rather than have the purlins sit in valleys that we created by overlapping hoops. We found in 2014 that we had abrasion problems with the netting where the netting was wedged between two overlapping hoops. This change to the wiggle wire system made the system even stronger, increased the amount of area that each piece of netting will cover, and decreased the number of hoops that a grower will need to cover a planting. In 2015, we also had zippered doorways made for our vestibule system. These worked extremely well, making it much easier to enter and exit the planting and have the vestibules properly closed.
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 control 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 .
Infestation data collected throughout the harvest season indicates that once again, the 80 gram insect exclusion netting was a great success. Berries were sampled every week from July 16 to August 18. Under the exclusion netting a total of 5 berries out of 1350 collected (0.37%) had SWD adults emerge from them under laboratory rearing conditions. In the control treatment, which received 5 applications of crop protection materials between July 23rd and August 17th, 14 out of 450 berries collected (3.10%) had SWD adults emerge from them. Commercial harvest ended on August 20th.
We did not have any problems with the netting being held in place by the use of wiggle wire. The wiggle wire system was a great advantage. We are going to change the attachment system at the ground level in 2016, changing it from wiggle wire on purlins laying on the ground to wiggle wire channel attached to inexpensive 1 x 6 boards attached to our metal hoops, like a baseboard on a high tunnel. It will be cheaper than purlins and by putting sand or gravel against the edges of the boards, we can eliminate areas where SWD may be able to enter the planting underneath the purlins.
Impacts and Contributions/Outcomes
We held a field day at the farm on September 2nd 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.
In 2015 I presented results from the 2014 trial at 2 SWD workshops held in NYS, the NYS Produce Expo, the CT Fruit and Vegetable Conference, and the mid-Atlantic Fruit and Vegetable Conference in Pennsylvania. So far, I have reached over 600 growers and Extension staff through these meetings. An article about the project, including my 2014 results was in the May issue of Fruit Growers News, a trade magazine out of Michigan that has nationwide distribution.
In 2012, I lost 40% of my blueberries to SWD – a $6200 loss. In 2014 and 2015, 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. I am hoping that I can get NRCS interested in providing cost-share assistance for this practice which will help adoption even more.
Professor of Entomology
NYS Ag Experiment Station
630 North Street
Geneva, NY 14456
Office Phone: 3157872345
Area Small Fruit Specialist
Cornell Cooperative Extension
415 Lower Main
Hudson Falls, NY 12839
Office Phone: 5187462562