This project evaluated the merits and costs of netting to exclude SWD from a blueberry planting, and attempted to evaluate mass trapping as an additional means of reducing Spotted Wing Drosophila (SWD) to mitigate the damage caused by SWD. The treatments were 1) netted 2) netted with sticky traps 3) netted with vinegar traps and 4) netted with weed matt (Lumite 994GC woven fabric ground cover) and 5) non-netted control with vinegar traps. Protek insect netting 1.00mm x .85mm was used in the trial. This netting is 80% porous and has 83% light transmission capabilities.
SWD pressure was non-existent to very-low with only 3 females found in one control trap. Due to the low SWD pressure, we were unable to make any determination on the efficacy of mass trapping for SWD.
Fruit yield was not negatively impacted by netting or fabric mulch. Overall yield was slightly higher in some of the netted treatments. Fruit quality was not negatively impacted by the netting. The % Brix was slightly higher in the netted treatments, but individual berry size was larger in the controls. There was no evidence of SWD oviposition in any of the berries examined throughout the trial. The temperature under netting was slightly higher and the light was slightly lower. These differences do not correlate with fruit quality and appear from this one season of observation to be insignificant. An observation made by pickers was that the netted treatments, especially the netted treatment with weed mat, ripened earlier by a few days than did the control. No measurements have been made yet on shoot regrowth although visual observation does not indicate any difference in habit.
For those growers who group their blueberries by variety, netting a block of late-season berries might be cost effective. Netting blueberries may be a viable strategy for organic or small acreage plantings. Growers who do not have bird netting in place might want to track the reduction in bird damage as a result of having insect netting installed. The yield improvement realized from reducing bird damage might be enough to encourage netting as a sustainable option for SWD management.
Unlike native species, SWD uses its saw-like ovipositor to deposit eggs in ripening fruit resulting in larval development inside the berry. Activity of the fruit fly corresponds to the ripening of blueberries, raspberries, day neutral strawberries and a variety of other cultivated and wild hosts. In 2012, levels of infestation reported state and region-wide ranged from 80-100% of fruit examined with individual fruit infested with as many as 25 larvae.
Traditional IPM, which relies on scouting to determine an economic threshold before pesticides are applied, has been temporarily abandoned. While monitoring for pest presence is still recommended, a 3-7 day insecticide spray schedule is currently the recommended management strategy. Organic berry growers are neither inclined nor prepared to use insecticides at this frequency, and their customers are particularly concerned about pesticide use. There are very few organically approved pesticides available, making it difficult to properly rotate chemicals.
The planting in question on my farm is quite young, however, we decided to be proactive and investigate netting as a control method. Research papers translated from Japanese by Cornell graduate student Masanori Seto provided the necessary incentive. (Netting control of Drosophila suzukii by Chiba Prefectural Agriculture Research Center & Chiba Industrial Technology Research Institute – Translated by Masanori Seto.) Laura McDermott from Cornell Cooperative Extension was the technical advisor who helped with insect ID and data analysis.
Hay Berry Farm grows perrenial blueberries and lavendar, annual cut flowers, herbs and pumpkins in Hoosick Falls, NY. We are certified organic and a U-Pick operation with a farm stand. Oh, and hay fields, of course.
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.
Protek insect netting 1.00mm x .85mm was used in the trial. This netting is 80% porous and has 83% light transmission capabilities. The suggested life of the net is 7 years but if stored well it may last several additional seasons. The net 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 used extra netting material fastened with pig rings. The treatments were netted after bloom and before berries began to color. The exclusion netting hung over wires placed at a height of 6’ to accommodate pickers. The wires, anchored to 2 H-braces at rows’ ends, were supported by posts set strategically along the row. The net was weighted down with construction grade water hose, which prevented ripping as well as lifting during high winds.
Five year old ‘Bluecrop’ plants comprised the randomized treatments which were replicated three times. We evaluated exclusion alone and in combination with two different types of traps – unbaited red solo cups covered with tanglefoot and a yeast baited trap that uses vinegar as a drowning solution. The treatments were 1) netted 2) netted with sticky traps 3) netted with vinegar traps and 4) netted with weed mat. Lumite 994GC woven fabric ground cover made of UV stabilized polypropylene allows passage of water, nutrients and air while suppressing weeds. The mat treatment was added as an afterthought and not part of the original proposal. The netted treatment was replicated 3 times, the control portion was only replicated once.
The final treatment was the # 5) non-netted control with vinegar traps. Each treatment was composed of 3 plants and fruit data was hand harvested twice weekly from the middle plant in the group for three weeks during peak production. The harvested berries were examined for % SWD infestation, individual fruit quality and yield. The insect traps were checked and changed weekly and numbers of SWD and other insects were recorded. Light intensity and temperature under the nets was taken and compared to the untreated control on a weekly basis. Shoot regrowth in the netted, fabric mulch and control treatments will be evaluated during the spring of 2014.
The plants were treated consistently throughout the experiment. No sprays were used during the 2013 growing season except for a Neem application to control scale in the spring. All other cultural inputs were identical across all treatments and the control including pest control, fertilization, and irrigation. No frost control was necessary. Bird netting and deer fencing were in place for all treatments.
SWD pressure was non-existent to very-low with only 3 females found in one control trap. As shown in Figure 1, the sticky traps and vinegar traps showed that the netting effectively excluded many other insects of similar and larger size. The sticky traps attracted a higher percentage of ants and crawling insects apparently not attracted to the yeast bait in the vinegar traps. Native drosophila were found in the control traps in very low numbers. No drosophilids were found in the traps in the netted treatments. Due to the low SWD pressure, we were unable to make any determination on the efficacy of mass trapping for SWD.
Fruit yield was not negatively impacted by netting or fabric mulch (Figure 2). Overall yield was slightly higher in some of the netted treatments.
Fruit quality was not negatively impacted by the netting. Fruit size was measured by using a caliper on 10 randomly selected fruit from each replication at each picking date. Those same berries were individually examined under a microscope for evidence of SWD oviposition and then they were crushed together for a % Brix reading using a hand held refractometer. As shown in Figures 3 and 4, % Brix was slightly higher in the netted treatments, but individual berry size was larger in the controls. There was no evidence of SWD oviposition in any of the berries examined throughout the trial.
We were concerned about the effect of the net on light and temperature in the netted treatments. Temperatures were recorded weekly through the trial in each of the replications of the control and the netted treatment with no traps or weed mat. The temperature is slightly higher on two of the dates measured (Fig. 5) and the light is slightly lower in all three of the dates measured (Fig. 6). These differences do not correlate with fruit quality and appear from this one season of observation to be insignificant. Light under the net – despite the 85% transmission rating – was still good most likely because the white color allowed it to get reflected throughout the netted area. This characteristic might be reduced as the netting ages. An observation made by pickers was that the netted treatments, especially the netted treatment with weed mat, ripened earlier by a few days than did the control.
No measurements have been made yet on shoot regrowth although visual observation does not indicate any difference in habit.
The weed mat did not have much impact on the data, although shoot regrowth over time will have to be monitored. One aspect that we liked was that dropped berries could be easily removed from planting simply with a broom and dustpan unlike the more problematic bark mulch. We also hope that fabric mulch will both reduce the humidity caused by weeds and raise the temperature under the plants, thus discouraging SWD.
The cost of covering an acre of blueberries with insect netting would likely range from $7000 to $9000 depending on the support system used. With a net life of 7 years, the amortized cost of an $8000 investment would be $1143/year, not including labor. Given that estimates for annual increases in cost of production per acre to control SWD range from $36 to $290 (Spotted wing drosophila impacts in the eastern United States. Developed by the eFly: Spotted Wing Drosophila Working Group. http://www.sripmc.org/WorkingGroups/eFly
/Impacts%20of%20SWD%20in%20the%20Eastern%20US%202012.pdf), netting blueberries may be a viable strategy for organic or small acreage plantings. Growers who do not have bird netting in place might want to track the reduction in bird damage as a result of having insect netting installed. The yield improvement realized from reducing bird damage might be enough to encourage netting as a sustainable option for SWD management.
We found several positive reasons to consider using insect netting. No drosophilids were found in the netted treatments and this netting design excluded flying insects of similar and larger size than drosophila. We did not find negative impact to fruit yield or fruit quality (size and % Brix).
Negatives include price of netting and installation as well as difficulty of storing bulky materials and protecting it from damage such as hail.
Positive reasons to expand use of weed mat include ease of cultural controls and reduced costs of labor for weeding. If the mat is rolled or cut back judiciously, we could encourage normal shoot regrowth, discourage moles and allow for spreading wood chip mulch. If berries ripen a few days earlier with the weed mat, the harvest of some blueberry varieties might end before SWD becomes an issue.
Education & Outreach Activities and Participation Summary
August 1, 2013 presentation at Cornell University’s 2013 Fruit Field Day at the NYS Agricultural Experiment Station about objectives and methods to fruit growers, consultants, and industry personnel. Evaluation of exclusion and mass trapping of SWD in organic blueberry production by Laura McDermott and Lawrie Nickerson
September 10, 2013 sponsored by Cornell University Cooperative Extension Eastern New York Commercial Horticulture. Field Meeting at Hay Berry Farm to growers, suppliers and extension consultants on Exclusion Netting and Mass Trapping to Control SWD in Organic Blueberries by Laura McDermott and Lawrie Nickerson.
January 23, 2014, Empire State 2014 Producers Expo, Oncenter Convention Center, Syracuse, NY. Education session on methods and results of Evaluation of exclusion and mass trapping of SWD in organic blueberry production by Laura McDermott and Lawrie Nickerson.
January 24, 2014 half-day intensive presentation on SWD research and the Hay Berry Farm exclusion field trial to farmers at NOFA-NY Conference in Saratoga Springs, NY. By Laura McDermott, Emily Cook, Timothy Lampasona (all of Cornell University Cooperative Extension) and Lawrie Nickerson.
Article in NY Fruit Quarterly, Spring 2014: Evaluation of Exclusion and Mass Trapping as Cultural Controls of Spotted Wing Drosophila in Organic Blueberry Production, by Laura McDermott, Cornell Cooperative Extension, Eastern New York Commercial Horticulture Program, and Lawrie Nickerson, Hay Berry Farm LLC.
For those growers who group their blueberries by variety, netting a block of late-season berries might be cost effective. Because our late-season berries are planted together, we are considering netting several rows of Nelson and Elliott varities, which ripen after SWD is known to arrive in our area. We will factor in costs of netting as well as results from 2014 experiments on a variety of other control methods. In addition, another local grower is trialing a larger-meshed, less-expensive, lighter-weight net, which would be a good choice if it works. We are interested in insect netting because of increased yields (by over 30%) using bird netting. Insect netting would double as bird netting in our new section, making installation more tempting.
Weed pressure impacts plant health and fruit production (shelter for insects, competition for nutrients, clean up, fruit yield) as well as labor costs, esthetics and ease of harvesting. Thoughtful use of weed mat along with insect netting might significantly impact insect behaviors as well as fruit quality, costs and customer satisfaction on organic and you-pick operations.