Practical exclusion netting for reducing disease vectors in high density apple systems

Final report for FNC18-1119

Project Type: Farmer/Rancher
Funds awarded in 2018: $22,050.00
Projected End Date: 02/28/2020
Grant Recipient: Might Oak Orchards
Region: North Central
State: Michigan
Project Coordinator:
Jordan DeVries
Mighty Oak Orchards
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Project Information

Description of operation:

Mighty Oak Orchards is a 2 1/2 acre farm in Northern Michigan, committed to the sustainable raising of heirloom apple trees for cider makers and old world apple lovers. The farm has been operating since 2015, having previously been an abandoned orchard. Sustainable practices that were carried out before this grant were related to water re-use and conservation through a rainwater collection system, and use of cereal rye as a cover crop and alfalfa legume as a soil conditioner. These practices started in 2016.


Apple scab and bacterial fireblight need frequent consideration in high density apple orchards. These close proximity and high growth-rate systems often have a drawback of increased disease management effort. Non-chemical disease control includes removing surrounding source-wood for these pathogens and insect vectors, planting disease-resistant varieties/rootstocks, and frequent scouting to remove infected parts of the trees.

Exclusion netting has been popular in Canada and France for reducing insect damage on apples at critical control periods and has shown promise in protecting blueberry crops from insects in the U.S. This cultural control has also shown promise for controlling apple scab in published research, while there isn’t much data on fireblight control. Theoretically, netting will reduce wind, rain and insect transport for the bacteria that causes fireblight. This has promise for producing organic high density apples in moist environments where fireblight occurs, as Streptomycin and Kasumin, are not organic certified. Queva, Double Nickel and Serenade are OMRI listed but less effective. They could have greater fireblight control activity in combination with exclusion netting. We will compare different netting materials and combinations of conventional and organic products to control these diseases and try to identify or reduce technical and labor hurdles to using netting.

Project Objectives:

1: Evaluate three different commercial exclusion nets and no-net control for durability, micro-climate effects, insect exclusion, and wind and rainwater passage factors at all three farms.

2: Test different fungicides and bacteriocides with the three exclusion nets and a no-net control in statistically significant tests to compare outcomes at three different orchards.

3: Investigate solutions to make exclusion netting easier to use in high-density orchards. Designs to pull the netting back over rows, open on one side, or have seal-able openings can make them practical.

4: Share findings through field days, website and social media, conference presentation.


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  • David Jones (Educator)


Materials and methods:

In the first year of this project, 2 year old feathered trees were planted into new orchard ground at Little Red Organics and Mighty Oak Orchards which served as the farms receiving experimental treatment of row netting. New cider variety tree plantings were trellised at 18" spacing on 8' rows. The trees were treated for fireblight during green tip with Queva Double Nickel, and subsequently applied with firewall and/or agrimycin streptomycin. Kasugamycin was not applied due to cost, and Apogee was not applied in order to reduce the potential for stunting trees. Row netting from Bluefire Farm supply was used exclusively in the first year as it was the least expensive product available. This netting was applied to 6 rows at each farm, in 150 foot lengths. At first, the netting was suspended over the top trellis wire that would eventually be used to support the trees. Two additional trellis posts at the outside of the perimeter of the planting were used to support a between row wire, which was used to keep the netting off the trees and their feathered branches that were not whipped back yet. Later on, EasyKlip clips and supporting S clips from Dubois Agrinovation were purchased to suspend the netting from the top wire and these intermediate wires between the rows. Irrometers were used to study soil moisture under the netting to help schedule irrigation events and monitor soil impacts of the netting microclimate effects. Temperature and humidity readings under the nets were also taken as data points and used as a proxy to monitor for the potential for the nets to reduce apple scab. Insect monitoring served as an important proxy for the ability to control fireblight. Dr. George Sundin at Michigan State University's Horticulture dept. was contacted about taking netting samples for research trials using Erwenia spp. (fireblight bacteria) inoculum.

Over the winter of 2018-19, it was found that the wind coming off of Lake Michigan caused a high amount of windshear and resulting cold temperature stress on the newly planted apple trees at the Mighty Oak and Little Red Organics Farms, which were more exposed than the Bedker Orchards site due to being on hillsides. The trees were not fully supported and needed additional posts and wires when the nets were removed the previous fall.  This required the purchase of an additional order of 60 12' Trellis posts to keep the netting off the trellised trees the following spring. Close to 100 trees were lost due to cold damage and not being supported properly on these exposed sites. It was difficult to find space for the additional trees and trellis posts in the existing 3 rows at each farm site, so a 4th row was created with additional posts, anchors, wire and netting. Because of this, there wasn't enough time to devise a more efficient net deployment system, so the standard net system from Dubois Agrinovation using the EasyKlip clips and S Klip travelers on the wire structure was used. This kept the nets from draping on the young and brittle apple tree branches at the top. Unfortunately there wasn't anything to hold the nets at the sides of the trees and significant rubbing and occasional branch breaking on windy days. 


Research results and discussion:

This summer proved interesting with regards to weather and the ability to deploy the nets effectively. One of the problems we foresaw with the nets, which proved true was that they might not be durable enough to be deployed over an individual trellis row, having to be instead draped over an entire trellis system. A large amount of rain hit Western Michigan in early May which affected our ability to plant trees as soon as we would have liked. This helped us miss the peak of the scab season because leaves were not at green tip yet, however it opened the trees to being vulnerable to fireblight bacteria, as the trees were just starting leafing out at the time of the start of the region's king bloom. This meant that pollinators would not be the culprit for potentially spreading fireblight to our trees, the main reason for the netting.  Instead we would have to worry about wind-dispersed Erwenia Spp.  spores, which the nets would be less likely to protect trees against. Luckily, no trees got fireblight in this year. We felt it was important to look at environmental factors underneath the netting vs. the no-netting control to see if moisture could be controlled enough to control the apple scab fungus, and if temperatures under netting could be manipulated to make a slightly less hospitable environment for the fireblight bacteria. What was found was the decreased light penetration, the manufacturer proports a 78% light penetration, helped to increase the longevity of high moisture conditions, but not necessarily increase the peak measurement of humidity or soil moisture. Temperature was seemingly unaffected by the row netting except in extreme conditions, either hot days with full sunshine or days with excessive wind, in which there was a slight muting effect. Because the nets were not deployed early enough in the season to be effective on insects that carry fireblight, the study on the ability to control the movement of certain insects, especially pollinators, is inconclusive. We are hoping to observe this in the following field season. The extra nets from Bluefire farm supply were used experimentally to develop more useful tall trellis net deployment systems, recognizing that the current state of row netting is to be used for ground vegetables in high tunnels, highbush blueberries and grapes. PVC support tubes were one system used for deployment, but we eventually settled on EasyKlips and S Clips from Dubois Agrinovation suspended over the trellis from a freestanding topwire and two lateral intermediate row wires, which could also support the netting hanging from the adjacent netting. One odd thing that was unexpected that was noticed was the increased row-lane grass growth under the netting as opposed to the nearby no-netting control. I would like to see if this holds true the following year, but it noticeably made weed and pest control seem to be more difficult, and I want to see if there is a pattern here.

In the spring of 2019, the decreased ability to control vegetation under the netting contributed to significant vole damage, even though rabbits were prevented from getting under the net. Mice were able to get underneath the tree protectors and without fear from predation girdle several 2nd year trees. This led to a forced re-planting to maintain adequate spacing for spray applications. In this second growing season, it was determined that the nets negatively influenced fruit set, even though the nets were not deployed during pollination in two out of the four study rows at each farm. This was likely due to the nets blowing in the wind and rubbing against the pollinated blossoms and/or immature fruit. At least two of the study participants found the nets helpful in reducing spray effort, including frequency of application, but more trouble than they were worth due to decreased fruit set and damage to the trees. At the end of season two, it was determined that the participants wanted to apply for an extension try an additional spring pollination season with additional EasyKlips and lateral wires to keep the sides of the net off of the sides and top of the 3rd year trees, however, an extension was never ultimately applied for though the participants attempted this correction in the spring of 2020.

Participation Summary
3 Farmers participating in research

Educational & Outreach Activities

1 On-farm demonstrations
1 Tours
1 Webinars / talks / presentations
1 Workshop field days
1 Other educational activities: Picture and caption in May 2018 issue of Fruit Grower News of netting system

Participation Summary:

16 Farmers participated
200 Ag professionals participated
Education/outreach description:

An annual tour for CSA members at Little Red Organics got to see the orchard netting deployment using the suspended beneath a top wire technique, which was the first time this system was tested. There was also opportunity for people to directly observe the different microclimate under the netting, as the tour took place on a hot sunny day in July. Next, Jordan from Mighty Oak Orchards got to present some of the findings at the Northwest Michigan Orchard and Vineyard Show in Traverse City on January 15-16. This was in front of an audience of about 100, and was tied into talking about wild animal exclusion from cropping areas for food safety reasons. Lastly, Jordan had a picture of the netting taken by Stephen Klosterman from Fruit Grower News with a caption about the orchard netting, which is going to be pictured in an upcoming article in the trade magazine.

In the Winter of 2019-2020 Jordan from Mighty Oak Orchards was able to do a poster presentation at the Great Lakes Horticultural Expo on Dec. 5-7 2019 and also have preliminary findings included with Michigan State University's Dr. Todd Einhorn's presentation on using netting to control fruit set and reduce mechanical thinning efforts at both the International Association of Fruit Producers annual meeting in Grand Rapids MI on Feb 10-13, as well as discuss the trials  working with removable insect netting using trellis frame support at the IAFP tour of farms throughout West Michigan on Feb 13th 2020. None of the farms in the Farmer-rancher grant were visited because they were too far from the venue, but educational materials were passed around on busses and Jordan was given an opportunity to speak to over 200 tour participants about the research findings. 


Learning Outcomes

16 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Lessons Learned:

This project taught me the value of perseverance and maintaining a positive attitude to learn from a situation even when the outcomes do not turn out as expected. Ultimately, it was discovered that the netting with .5 and .32 mg per square cm from Bluefire farm supply and Dubois Ag. Innovations was too impassable for strong winds, acting as a sail that caught strong winds at two of the most exposed sites, pulling down apple trellis wires and otherwise damaging branches and main trunks of several fruit trees, breaking some off at the graft union. This affected my farm operation and the trees planted at Little Red Organics by requiring the replacement of several trees throughout the project. For Summer 2020 we chose to go through a less-heavy .25 mg per square cm net from Dubois Ag innovations along with extra S- clips and rigging that was placed in Summer 2020. This netting also moved around significantly in strong winds but resulted in less damage to trees and the effect on crop load through mechanical thinning. The nets had a seemingly positive effect on large apple pests such as apple maggot and codling moth, but also resulted in higher numbers of wooly apple aphid and spider mites. An initial reduction in apple scab on untreated trees was thought to be through a result of reduced rainfall splashing on apple scab spores, but later in the spring spore rods were able to collect significant spore activity through wind release and through the action of the nets rubbing on the ground. Lastly, none of the trees were infected with Erwinia (fireblight) bacteria through the trial, even in non-sprayed controls. This is evidence that the nets limited insect-transmitted spread of fireblight bacteria, as well as had some benefit to reduce wind-transmitted spread. However, the reduction in the potential for fireblight infection was determined to not outweigh the tradeoff of replacing/repairing damaged nets and rigging, replacing damaged fruit trees, increased aphid and mite presence and probable increase in Apple Scab infection. If other farmers or Ranchers asked about the recommendation to use over-row netting on trellised apple trees,  it would be better to go with lighter weight nets, or extra rigging, and only use the nets in the critical fireblight control period during the bloom period. If high winds were prevalent at the site, it would be recommended that they either do not use the netting or have a good system or plan to pull nets off the trees during the wind event. The wind shear was an unforeseen factor in planning this project that we thought could be managed through rigging and weighting at the bottom of the nets, but it's our impression that it is nearly impossible to control.

Project Outcomes

1 New working collaboration
Success stories:

Nothing of significance yet, first year of project.

Information Products

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.