Organic Apple Production In High Tunnels

Final report for FNC20-1238

Project Type: Farmer/Rancher
Funds awarded in 2020: $9,000.00
Projected End Date: 01/31/2022
Grant Recipient: Two Onion Farm
Region: North Central
State: Wisconsin
Project Coordinator:
Christopher McGuire
Two Onion Farm
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Project Information

Description of operation:

My wife Juli and I have operated Two Onion Farm since 2003. From 2003-2017, we raised up to 5 acres of organic mixed vegetables. We have raised organic apples since 2012, and we now have two acres of apples outdoors (not in high tunnels) in addition to one-quarter acre each of currants and gooseberries. We transitioned our farm from vegetables to fruit to meet a strong market demand for local organic fruit and to protect our hillside soils from erosion with perennial crops. We market our apples through a community-supported agriculture (CSA) program, to local grocery stores and chefs, and by processing them into applesauce and apple butter.

We raise trellised dwarf trees in our outdoor apple orchard. We grow disease-resistant varieties which require minimal organic sprays. We use bark mulch under our trees to reduce weed competition, supply nutrients and organic matter, and nourish beneficial soil fungi. We encourage beneficial insects in the orchard, scout daily for pests, monitor weather to predict pest outbreaks, and only spray organic pesticides as a last resort.

We constructed our first high tunnel in 2011 and currently have three high tunnels on our farm. In two previous years we raised nursery apple trees in high tunnels (these were grafts raised for one year in the high tunnel before being dug and transplanted to a permanent location). We were impressed by the vigorous growth and the absence of disease in these high tunnel nurseries; this motivated us to consider growing apples permanently inside tunnels.

Our farm infrastructure includes a packing shed, three walk-in coolers, and two tractors with implements for tillage, cultivation, mowing, spraying, and spreading amendments.

Summary:

Locally produced organic apples are in demand, but most organic apples are produced in desert areas of Washington, where the dry climate reduces infection from fungal diseases such as apple scab.  In the north central U.S., wetter weather favors disease, and most organic apple growers grow disease-resistant varieties and/or spray organic fungicides such as sulfur.  Disease-resistant varieties can be difficult to market if they are not the most flavorful varieties or if they are not familiar to consumers.   Organic fungicide sprays are expensive, require frequent re-application, and can have negative effects on apple trees, beneficial insects, and the environment.  Trees grown in polyethylene-covered tunnels are protected from rain and should therefore suffer less disease.  In this project we evaluated the growth, yield, and profitability of seven apple varieties grown organically in unheated polyethylene-covered high tunnels.  We raised trellised, dwarf trees using the tall spindle training method.

We planted our high tunnel trees in spring 2019 and have raised them for three growing seasons, with harvests in 2020 and 2021.  Key observations and conclusions from our project are:

  • Trees grew vigorously and filled the available space quickly.  With timely branching training and notching of the leader, trees developed a good structure and have not outgrown their space.
  • Covering tunnels with opaque silage tarp in winter was an effective way to prevent winter damage from rapidly fluctuating temperatures.
  • Virtually no diseases other then powdery mildew were observed in the tunnels.
  • Insect damage to foliage and fruit in the tunnels was common and overall at a similar level to what we normally see in outdoor trees.
  • Flowers in the tunnel suffered significant frost damage in 2020 during a bloomtime freeze event.
  • Fruit of many varieties suffered significant heat-related defects in the tunnels.
  • Average yields were 7 lbs/tree in 2020 and 25 lbs/tree in 2021 (about 200 lbs per acre and 750 lbs per acre, respectively)
  • Varieties differed enormously in yield and susceptibility of their fruit to heat damage.
  • Although myriad factors affect profitability, we estimate that on our farm it would take 10+ years to recoup the costs of constructing tunnels and planting apple trees in them.

We have shared project results through a field day, conference poster session, a published report on our website, emails, and press releases.  Four periodicals aimed at farmers have agreed to publish a summary of our project in 2022.

Project Objectives:
  1. Measure costs, yields, and profitability of organic apples raised in high tunnels.
  2. Compare yields and profitability of seven apple varieties in high tunnels.
  3. Measure incidence of common apple diseases and insect pests in high tunnels.
  4. Share results with other growers through our website, a field day, emails to grower list-serves, articles in grower publications, and a conference poster session.

Research

Materials and methods:

We established the high tunnel plantings in April 2019 and we collected data through the 2021 growing season.  (Some of the activities described here occurred before the start of the grant project period and were not funded by the grant, but we are including them here to give a complete context for the project).

Organic.  Our entire farm is certified organic by MOSA (mosaorganic.org) and only organic methods were used in this research. 

Planting Arrangement.  There were thirteen trees of each variety in each tunnel, along with 1-2 border trees at each end of each row.  (Data from border trees is not included in this report).  Within each tunnel, the 91 non-border trees were arranged randomly, with varieties randomly interspersed.  Trees were planted 3' apart within the row, with 11-12' between rows.

Planting high tunnel apples

Varieties.  We selected seven apple varieties for this study: Ashmead’s Kernal, Grimes Golden, Macoun, Hudson’s Golden Gem, and Golden Russet are less common heirloom varieties which can command a high price because of their flavor and historical interest.  However, all are susceptible to scab and other diseases and we therefore do not raise them outdoors.  Unfortunately, the scionwood which we obtained for Macoun and Grimes Golden was not true to type.  The Macoun trees were actually Calville Blanc d’Hiver.  The putative Grimes Golden trees were of an unknown red/green skinned, sweet, soft-fleshed apple, referred to as Mystery hereafter.  The other two varieties in our study, Winecrisp and Suncrisp, are high-yielding modern varieties popular with local organic growers.  We have raised these varieties outdoors.  Winecrisp is scab-immune, but fairly susceptible to cedar-apple rust and Alternaria blotch.  Suncrisp is moderately resistant to scab, but not immune.  We included these two varieties as a comparison to the five heirloom varieties because they are reliable standards and because they are heat-tolerant and thus may thrive in warm high tunnels.

High Tunnels.  Two high tunnels purchased from Nolt’s Midwest Produce Supplies were used in this study; both allow trees to reach heights of 10+′ and are ventilated via rollup sides and endwall doors:

Tunnel Width Length Number of Tree Rows Trees Per Row Total Trees Border Trees1 Experimental Trees2 Year Constructed Initial Construction Cost (Materials Only)
1 34' 102' 3 33 99 8 91 2017 $9,643
2 24' 148' 2 49 98 7 91 2018 $9,955

1Border Trees are at the ends of rows; no data was collected from these trees
2Experimental Trees are the trees from which data was collected

High Tunnel Coverings.  When the trees were planted in April 2019, the tunnels were covered with a single layer of standard greenhouse polyethylene.  We removed the plastic prior to winter (on 10/25/2019 from tunnel 1, and on 12/5/2019 from tunnel 2).  Based on the experience of farmers and researchers with other tree fruits, it is important to not expose trees to the drastic diurnal temperature fluctuations that occur in winter in high tunnels covered with clear greenhouse polyethylene.  On sunny days, temperatures can rise steeply in tunnels covered with clear plastic, but at night the temperatures inside the tunnel are similar to outdoor temperatures.  Trees cannot remain cold-hardy and acclimated under these constant temperature swings and are likely to suffer cold damage at night.  In spring 2020, we covered both tunnels using a single layer of Klerks SunView Cool polyethylene, which lowers tunnel temperatures by approximately 10 degrees compared to the traditional polyethylene covers (tunnel 1 was covered on 5/2/2020, and tunnel 2 on 5/6/2020).  We selected the SunView Cool cover because the trees suffered leaf burn during warm spells in 2019 and because apple fruits are vulnerable to sunburn at air temperatures above 95 degrees.  For the winter of 2020-21, we elected not to uncover the tunnels because of the time required, the stress and difficulty of re-covering tunnels during windy early spring weather, and the risk of damaging the cover during removal and reinstallation.  Instead, on 11/23/2020 we covered both tunnels with Film-Gard black and white 5 mil silage tarp (available at Farm and Fleet).  The tarp was installed white side out, and completely covered the south, east, and west sides of each tunnel, preventing winter sunlight from entering the tunnel.  We had heard from other growers who raise stone fruits in high tunnels that the silage tarp keeps the tunnel cool in winter and prevents daytime temperature spikes.  The silage tarp was removed on 4/6/2021.

Tunnel 1 covered with silage tarp

For ventilation, rollup sidewalls and endwall doors were regularly left open during the growing season.  Before mid July, we attempted to close the tunnels during rain to minimize the chance that windblown rain would wet foliage and lead to disease.  Later in summer and in fall we no longer closed the tunnels during the rain.

Tree Planting.  The trees planted were one year old grafts raised in our on-farm nursery or purchased from Cummins Nursery, Trumansburg, NY. We planted trees by hand on April 12th and 17th, 2019.

Mulch and Weed Control.  We completely covered the soil surface in both tunnels with hardwood bark purchased from local sawmills after planting.  Tunnel 1 was mulched in May 2019, but Tunnel 2 was not mulched until November 2019 because of time constraints.  Both tunnels were hand weeded as needed during the growing seasons.  Compared to outdoor plantings, the mulch in the tunnels degraded slowly (presumably because of lack of rainfall), and it was not necessary to replenish the mulch during the first three years of growth.

Mulched trees, early summer 2020

Irrigation.  Both tunnels were irrigated using drip tape with a flow rate of 0.34 GPM per 100', with a single tape line by each tree row.  Irrigation sessions were generally for 8-12 hours on 4-7 day intervals, depending on weather.

Training.  Trees were planted 3′ apart within rows, grafted on dwarfing rootstocks (G. 41 or G.11) and trained using the tall spindle method; these are common practices in outdoor high-density apple orchards. 

In the 2019 growing season, we trained trees on a minimal wire trellis suspended from the high tunnel structure.  Trees were secured to the wires with tree tie tape, and vigorous branches were tied below horizontal using training wires. 

In April, 2020 we installed a permanent support stake next to each tree (Best Angle Tree Stake model PA3120 - 10' high angle iron stake 1-1/4" x 1-1/4"); stakes were pounded 2.5' into the ground, with 7.5' above ground.  We secured trees to the stakes with AgLok chain and continued to train vigorous branches below horizontal using training wires.  On 4/2/2021, we dormant pruned the trees, removing several larger branches from each tree.  In 2021, we continued to train trees to the metal stakes, but did minimal branch training.

To encourage branching, we notched the cambium above dormant buds on the leader in all three  years (4/22-4/29/2019, around green tip; 5/5-5/8/2020, just before bloom; and 4/16-4/17/2021, at green tip to tight cluster).   On one year old wood, we notched by running the saw blade on a Leatherman tool backwards to abrade the cambium just above the bud.  On two year old wood, we used a box cutter knife: we pressed the blade straight into the hardwood just above the bud, then made a second cut down at a 45-degree angle to meet the straight cut and we removed the angled notch.  Extensive blind wood on leaders is unacceptable in high density apple production; notching is highly effective at promoting branching.

In general, vegetative vigor was high, and we were initially concerned that the trees might outgrow their space over time, but fruiting definitely reduced vigor in the second and third years.  Most leaders were close to the roof of the high tunnel by the end of 2020 and were pressing against the roof by the end of 2021.  Repeated rounds of branch training were required in both 2019 and 2020.  The variety Suncrisp was particularly troublesome because of its propensity to grow strong upright branches.

Young branches trained downward with training wires

Insect Pest and Diseases.  We scouted each high tunnel weekly for disease and insect pests.  In addition we installed delta traps baited with pheromone lures for codling moth, red-banded leafroller, and oblique-banded leafroller in tunnel 1.  Virtually no signs of plant disease were noted in the tunnels. In 2020, a few cedar apple rust lesions occurred on early spur leaves of Golden Russet and Hudson's Golden Gem; it is likely that these infections may have occurred shortly before the tunnels were covered in early May.  In 2021, occasional cedar apple rust lesions were noted on many varieties, especially near the edges of the tunnels, and we suspect that infections occurred when the rollup sides were left open during a spring rain event.  In both years, the cedar apple rust levels in the tunnels were vastly lower than in our outdoor orchard.   Fireblight, scab, Elsinoe leaf spot, alternaria blotch, sooty blotch and flyspeck were all absent or vanishingly rare.  All of these diseases occurred in our outdoor orchard during 2020 and 2021.  The virtually pristine foliage on tunnel trees, even in mid to late autumn, was remarkable and unprecedented in our experience growing organic apples outdoors.  The one notable exception was that in late summer 2021 we observed low levels of powdery mildew in both tunnels on numerous varieties.  Powdery mildew is generally common in high tunnels because warm, humid conditions favor its development, and because it does not require wet foliage to infect leaves. This disease is absent or very rare in our outdoor orchards, presumably because the conditions there are less favorable and/or our intensive spray program controls it.  We suspect that powdery mildew might continue to develop and spread in our tunnels in future years and that potassium bicarbonate sprays might be needed to control it.

In general, the tunnels did not appear to greatly reduce insect pest damage compared to outdoor orchards.  This observation agrees with what growers and researchers have found for other fruit crops grown in high tunnels.  The table below details our observations of insect pest damage in the tunnels and sprays used to control insect pests.

Insect

Occurrence in tunnels

Sprays made in tunnels

Qualitative Comparison of Damage in Tunnels to Damage in Nearby Outdoor Orchard

Codling Moth

2 moths caught in tunnel pheromone trap in 2020, none in 2021.  1st and 2nd generation larval feeding damage seen in tunnel 2 in 2021

Granulosis virus sprayed for both 1st and 2nd generations in both years.

Significantly greater level of damage in tunnel 2 in 2021 than outdoors.  Outdoors, mating disruption and more extensive granulosis sprays are used to control CM.

Japanese Beetle

Low levels of damage noted in 2021

beetleGONE sprayed in 2020 but not 2021

Lower damage in tunnels than outdoors

Red banded leafrollers

Regularly caught in pheromone traps and some damage noted to terminals

Dipel (Bt) sprayed during larval activity

Similar level of damage

Oblique banded leafroller

Occasionally caught in pheromone traps and some damage noted to terminals

Dipel (Bt) sprayed during larval activity

Similar level of damage

Plum Curculio

In 2020, damage was seen in tunnel 2 while hand thinning.  Approximately 10 damaged fruits were found.  This is a low level of damage.  Much higher levels of damage were seen in 2021 in both tunnels.

Pyganic sprayed on warm nights during oviposition period

Greater level of damage in tunnels.  In outdoor orchard, we spray Surround heavily to deter PC.  We opted not to spray Surround in the tunnels out of concern that the residue would not wash off before harvest without rainfall.

Spider mites

In 2020, spider mite damage to foliage was evident in tunnel 1.  Lower levels of damage noted in 2021 in both tunnels

JMS Stylet Oil (horticultural oil) sprayed regularly in 2020.

Greater damage in tunnels.  Spider mites are not a pest in our outdoor orchard, and they are presumably favored by the dry conditions within the high tunnel.

Rosy apple aphid

Rosy apple aphid infestation occurred in both tunnels in late May and June, 2020

In 2020, infestations were controlled by localized spraying of Safer soap (1 tsp/1 cup water) with a hand spray bottle.  In several cases, the aphid infestation grew to significant size before we noticed it and multiple time-consuming sprays were needed to eradicate the aphids, showing the importance of timely scouting for this pest.

Greater level of damage in tunnels.

Wooly apple aphid

Numerous infestations noted in both tunnels in 2021.  Some were very large and covered multiple branches.

Venerate sprayed in summer 2021

Greater level of damage seen in tunnels.  Outdoors, infestations are seen but rarely develop to significant size.  Tunnel infestations were larger. 

Potato leafhopper

Common during summer in all years

Azaguard sprayed in 2020

Similar – this insect is abundant and widespread in our outdoor orchards during the summer and consistently damages foliage.

Brown marmorated stink bug

One adult seen during harvest in fall 2021

None

Similar – this insect is very rare in our outdoor orchards.

Apple Maggot

No damage seen in tunnels

None

Similar – this insect is very rare at our farm.

Spray Schedule.  We sprayed insect control products at several times.  In general, we made no disease controls sprays.  We sprayed micronutrients on the same schedule as used for outdoor apple plantings.  Sprays were applied using a Rears Pakblast 50 tractor mounted airblast sprayer, except for safer soap which was spot-sprayed on aphid-infested foliage.  All sprays are shown in the table below.  The high tunnel plantings were certified organic and all sprays were organically approved.  We were unable to spray the outside of the outside rows in both tunnels because the tractor would not fit there.  I.e., in Tunnel 1, which had three rows of trees and two drive aisles, the middle row was sprayed from both sides but the outer two rows were sprayed from one side only.  In Tunnel 2, which had two tree rows and one drive aisle, both rows were sprayed on one side only.

Date

Product and rate

05-Apr-20

JMS Organic Stylet Oil 1 Quart per 100 gallons spray per acre

20-Apr-20

Clean Manganese 1 Quart per 50 gallons spray per acre

20-Apr-20

Clean Zinc 1 Quart per 50 gallons spray per acre

20-Apr-20

Clean Iron 2 Cup per 50 gallons spray per acre

20-Apr-20

Clean Symspray 0-0-1 1 Cup per 50 gallons spray per acre

20-Apr-20

Clean Copper 2 Cup per 50 gallons spray per acre

20-Apr-20

Clean Calcium 1 Quart per 50 gallons spray per acre

03-May-20

Dipel 2 Lb per 50 gallons spray per acre

03-May-20

Clean Calcium 2 Quart per 50 gallons spray per acre

03-May-20

Clean Manganese 1 Quart per 50 gallons spray per acre

03-May-20

Clean Symspray 0-0-1 1 Cup per 50 gallons spray per acre

03-May-20

Regalia 4 Cup per 50 gallons spray per acre

07-May-20

Clean Potassium 0-0-6 6 Quart per 50 gallons spray per acre

21-May-20

Regalia 4 Cup per 50 gallons spray per acre

21-May-20

Clean Symspray 0-0-1 2 Cup per 50 gallons spray per acre

21-May-20

Dipel 2 Lb per 50 gallons spray per acre

21-May-20

Lifegard 4 Oz per 50 gallons spray per acre

21-May-20

Clean Calcium 2 Quart per 50 gallons spray per acre

31-May-20

Clean Iron 4 Cup per 50 gallons spray per acre

31-May-20

Clean Manganese 1 Quart per 50 gallons spray per acre

31-May-20

Clean Calcium 2 Quart per 50 gallons spray per acre

31-May-20

Kinetic Nonionic Surfactant and Silicone Surfactant Blend 3 Fl oz per 25 gallons spray per acre

31-May-20

Sil-Matrix 1 Quart per 25 gallons spray per acre

31-May-20

Clean Symspray 0-0-1 1 Cup per 50 gallons spray per acre

03-Jun-20

Citric Acid 12.5 Fl oz per 50 gallons spray per acre

03-Jun-20

Pyganic 15 Cup per 60 gallons spray per acre

06-Jun-20

Citric Acid 4 Fl oz per 100 gallons spray per acre

06-Jun-20

JMS Organic Stylet Oil 4 Quart per 100 gallons spray per acre

06-Jun-20

Clean Calcium 4 Quart per 100 gallons spray per acre

06-Jun-20

Azaguard 2 Cup per 100 gallons spray per acre

08-Jun-20

Pyganic 15 Cup per 50 gallons spray per acre

08-Jun-20

Citric Acid 15 Fl oz per 50 gallons spray per acre

12-Jun-20

Azaguard 2 Cup per 100 gallons spray per acre

12-Jun-20

Citric Acid 4 Fl oz per 100 gallons spray per acre

12-Jun-20

JMS Organic Stylet Oil 4 Quart per 100 gallons spray per acre

14-Jun-20

Clean Calcium 4 Quart per 100 gallons spray per acre

17-Jun-20

Molasses 3.33333333333333 Cup per 50 gallons spray per acre

17-Jun-20

Madex 1.25 Fl oz per 50 gallons spray per acre

21-Jun-20

Clean Calcium 4 Quart per 100 gallons spray per acre

21-Jun-20

Clean Manganese 1 Quart per 100 gallons spray per acre

21-Jun-20

Clean Zinc 1 Quart per 100 gallons spray per acre

23-Jun-20

Dipel 2 Lb per 100 gallons spray per acre

23-Jun-20

Madex 1.5 Fl oz per 100 gallons spray per acre

23-Jun-20

Molasses 4 Cup per 100 gallons spray per acre

23-Jun-20

Surround 50 Lb per 100 gallons spray per acre

25-Jun-20

JMS Organic Stylet Oil 4 Quart per 100 gallons spray per acre

25-Jun-20

Azaguard 2 Cup per 100 gallons spray per acre

25-Jun-20

Citric Acid 4 Fl oz per 100 gallons spray per acre

28-Jun-20

Clean Calcium 4 Quart per 100 gallons spray per acre

29-Jun-20

Sil-Matrix 4 Quart per 100 gallons spray per acre

29-Jun-20

Madex 1.5 Fl oz per 100 gallons spray per acre

29-Jun-20

Dipel 2 Lb per 100 gallons spray per acre

29-Jun-20

Kinetic Nonionic Surfactant and Silicone Surfactant Blend 8 Fl oz per 100 gallons spray per acre

02-Jul-20

JMS Organic Stylet Oil 4 Quart per 100 gallons spray per acre

02-Jul-20

Azaguard 2 Cup per 100 gallons spray per acre

02-Jul-20

Citric Acid 2 Fl oz per 100 gallons spray per acre

05-Jul-20

Clean Calcium 4 Quart per 100 gallons spray per acre

05-Jul-20

Dipel 2 Lb per 100 gallons spray per acre

08-Jul-20

Madex 1.40625 Fl oz per 50 gallons spray per acre

08-Jul-20

Molasses 3.75 Cup per 50 gallons spray per acre

12-Jul-20

Citric Acid 3 Fl oz per 100 gallons spray per acre

12-Jul-20

JMS Organic Stylet Oil 4 Quart per 100 gallons spray per acre

12-Jul-20

Azaguard 2 Cup per 100 gallons spray per acre

17-Jul-20

JMS Organic Stylet Oil 4 Quart per 100 gallons spray per acre

17-Jul-20

Citric Acid 3 Fl oz per 100 gallons spray per acre

17-Jul-20

Azaguard 2 Cup per 100 gallons spray per acre

20-Jul-20

BeetleGone 2.5 Lb per 100 gallons spray per acre

20-Jul-20

Clean Calcium 4 Quart per 100 gallons spray per acre

20-Jul-20

Dipel 2 Lb per 100 gallons spray per acre

20-Jul-20

Clean Manganese 2 Quart per 100 gallons spray per acre

29-Jul-20

Dipel 2 Lb per 100 gallons spray per acre

29-Jul-20

Azaguard 2 Cup per 100 gallons spray per acre

29-Jul-20

JMS Organic Stylet Oil 4 Quart per 100 gallons spray per acre

29-Jul-20

Citric Acid 3 Fl oz per 100 gallons spray per acre

30-Jul-20

Clean Manganese 2 Quart per 100 gallons spray per acre

30-Jul-20

BeetleGone 2.5 Lb per 100 gallons spray per acre

30-Jul-20

Venerate XC 2 Quart per 100 gallons spray per acre

30-Jul-20

Dipel 2 Lb per 100 gallons spray per acre

30-Jul-20

Clean Calcium 4 Quart per 100 gallons spray per acre

07-Aug-20

Kinetic Nonionic Surfactant and Silicone Surfactant Blend 8 Fl oz per 100 gallons spray per acre

07-Aug-20

Sil-Matrix 4 Quart per 100 gallons spray per acre

09-Aug-20

Clean Calcium 4 Quart per 100 gallons spray per acre

09-Aug-20

Madex 1 Fl oz per 100 gallons spray per acre

09-Aug-20

Venerate XC 2 Quart per 100 gallons spray per acre

09-Aug-20

Dipel 1 Lb per 100 gallons spray per acre

09-Aug-20

BeetleGone 0.9375 Lb per 100 gallons spray per acre

09-Aug-20

Molasses 4 Cup per 100 gallons spray per acre

21-Aug-20

Clean Calcium 4 Quart per 100 gallons spray per acre

21-Aug-20

Venerate XC 2 Quart per 100 gallons spray per acre

21-Aug-20

Madex 1 Fl oz per 100 gallons spray per acre

21-Aug-20

Molasses 4 Cup per 100 gallons spray per acre

30-Aug-20

Madex 1 Fl oz per 100 gallons spray per acre

30-Aug-20

Molasses 4 Cup per 100 gallons spray per acre

30-Aug-20

Venerate XC 2 Quart per 100 gallons spray per acre

30-Aug-20

Clean Calcium 4 Quart per 100 gallons spray per acre

30-Aug-20

Dipel 1 Lb per 100 gallons spray per acre

07-Apr-21

JMS Organic Stylet Oil 8 Quart per 100 gallons spray per acre

18-Apr-21

Clean Manganese 0.5 Quart per 50 gallons spray per acre

18-Apr-21

Clean Copper 2 Cup per 50 gallons spray per acre

18-Apr-21

Clean Iron 2 Cup per 50 gallons spray per acre

18-Apr-21

Clean Zinc 0.5 Quart per 50 gallons spray per acre

25-Apr-21

Clean Zinc 0.5 Quart per 50 gallons spray per acre

25-Apr-21

Clean Manganese 0.5 Quart per 50 gallons spray per acre

25-Apr-21

Dipel 2 Lb per 50 gallons spray per acre

12-May-21

Clean Calcium 4 Quart per 100 gallons spray per acre

12-May-21

Dipel 2 Lb per 100 gallons spray per acre

12-May-21

Clean Iron 4 Cup per 100 gallons spray per acre

12-May-21

Clean Zinc 0.5 Quart per 100 gallons spray per acre

12-May-21

Clean Manganese 1 Quart per 100 gallons spray per acre

21-May-21

Citric Acid 2.2 Fl oz per 100 gallons spray per acre

21-May-21

Pyganic 26.6666666666667 Cup per 100 gallons spray per acre

21-May-21

Clean Calcium 4.16666666666667 Quart per 100 gallons spray per acre

01-Jun-21

Pyganic 26.6666666666667 Cup per 100 gallons spray per acre

01-Jun-21

Citric Acid 2.2 Fl oz per 100 gallons spray per acre

06-Jun-21

Madex 1 Fl oz per 100 gallons spray per acre

06-Jun-21

Clean Calcium 4 Quart per 100 gallons spray per acre

14-Jun-21

Clean Calcium 4 Quart per 100 gallons spray per acre

14-Jun-21

Madex 1 Fl oz per 100 gallons spray per acre

30-Jun-21

Clean Calcium 4 Quart per 100 gallons spray per acre

30-Jun-21

Dipel 4 Lb per 100 gallons spray per acre

30-Jun-21

Nu-Film P 12 Fl oz per 100 gallons spray per acre

13-Jul-21

Madex 1.28 Fl oz per 100 gallons spray per acre

13-Jul-21

Venerate XC 2 Quart per 100 gallons spray per acre

13-Jul-21

Clean Calcium 4 Quart per 100 gallons spray per acre

13-Jul-21

Nu-Film P 12 Fl oz per 100 gallons spray per acre

30-Jul-21

Dipel 4 Lb per 100 gallons spray per acre

30-Jul-21

Clean Calcium 4 Quart per 100 gallons spray per acre

30-Jul-21

Nu-Film P 12 Fl oz per 100 gallons spray per acre

30-Jul-21

Madex 1.28 Fl oz per 100 gallons spray per acre

17-Aug-21

Clean Calcium 4 Quart per 100 gallons spray per acre

17-Aug-21

Dipel 4 Lb per 100 gallons spray per acre

17-Aug-21

Lifegard 6 Oz per 100 gallons spray per acre

17-Aug-21

Carb-o-nator 5 Lb per 100 gallons spray per acre

17-Aug-21

Nu-Film P 16 Fl oz per 100 gallons spray per acre

17-Aug-21

Venerate XC 3 Quart per 100 gallons spray per acre

17-Aug-21

Madex 2 Fl oz per 100 gallons spray per acre

28-Aug-21

Lifegard 3 Oz per 50 gallons spray per acre

28-Aug-21

Venerate XC 1.5 Quart per 50 gallons spray per acre

28-Aug-21

Madex 1 Fl oz per 50 gallons spray per acre

28-Aug-21

Nu-Film P 6 Fl oz per 50 gallons spray per acre

28-Aug-21

Carb-o-nator 2.5 Lb per 50 gallons spray per acre

Pollination.  A Koppert Natupol Excel Startup bumblee colony was placed in each tunnel near the beginning of bloom in each year (on 5/7/2020 and on 4/27/2021) to ensure adequate pollination.  We noticed that bumblebee workers from the introduced colonies regularly foraged outside the tunnel, and appeared to actually prefer foraging in the nearby outdoor field orchard.  However, bee activity was high inside the tunnels on rainy days.  Overall, initial fruitset was high and pollination appears to have been adequate.

Spring bloom and frost damage.  In 2020, high tunnel trees bloomed synchronously with field-grown trees, with first flowers opening on 5/12-5/13.  (Note, however, that the tunnels were uncovered before 5/2-5/6).  Nighttime temperatures in our outdoor orchard reached 28 degrees F on the morning of 5/9 under clear skies with a calm wind, shortly before bloom and when flower buds were very susceptible to cold damage.  On this cold night, we kept endwall doors and rollup sides on the tunnels completely closed in an attempt to retain warmth.  We found no damage to flowers in the field orchard from this cold event.  However, king blooms on most high tunnel varieties were killed (pistils were blackened).  In addition most Calville Blanc d’Hiver fruits in the high tunnel which did develop showed blossom end russeting which is commonly associated with frost damage at bloom.  We did not have a thermometer in the tunnels but we suspect that the temperatures were actually colder in the tunnel than outside.  Other high tunnel growers in our region have noted that nighttime temperatures can be lower in tunnels than outdoors during radiation frost events.  Tunnel 2 also occupies a slightly lower position on our hillside than our outdoor orchards, which may also have contributed to the frost damage in that tunnel.

In 2021, high tunnel trees bloomed synchronously with field-grown trees, with first flowers opening on 4/27.  (When we removed the silage tarps from tunnels on 4/6/2021, we noted that trees in the tunnels were behind outdoor trees in their stage of development.  Thereafter tunnel trees gradually caught up with outdoor trees in their developmental stage.)  When both outdoor and tunnel trees were in tight cluster stage, on April 21, outdoor temperatures reached a low of 25 degrees under clear skies with a calm wind.  During this cold night, we kept end wall doors and rollup sides in the tunnels completely open.  After this frost event, we observed very low levels of frost damage to blooms in the outdoor orchard, and no damage in the tunnels.  We have heard speculation that on calm nights, temperatures in tightly closed tunnels can be lower than outdoor temperatures and it is best to leave tunnels open on calm cold nights, and our experiences appear to bear that out.

Summary of Spring Phenology and Bloom in 2020 and 2021

Year

Winter Status of Tunnels

Date Tunnels Covered/Uncovered

Date of First Bloom in Tunnels

First Bloom Date in Outdoor Orchard

Frost Damage in Tunnels During Bloom

2020

Uncovered

Covered with clear poly on 5/2-5/6

5/12

5/12

5/9: outdoor temperatures reached 28 degrees F, at pink stage of bloom development. Tunnels were closed at this time and king blooms suffered serious damage.  No damage in nearby outdoor orchard

2021

Covered with clear poly and a white/black silage tarp

Silage tarp removed on 4/6

4/27

4/27

4/21: outdoor temperatures reached 25 degrees F at tight cluster stage.  Endwalls doors and rollup sides in tunnels were left open.  No damage seen in tunnels; slight damage observed in outdoor outchard

Frost Damaged Flower, May 2020
Frost cracks on Calville Blanc fruitlet

Thinning.  In 2019, we removed any developing fruit after bloom.  In 2020, we hand-thinned fruits, aiming for 1-3 (occasionally 4) fruits per branch, depending on branch length, and 1-4 additional fruits on the leader.  Thinning was performed on 6/1 and 6/9, about 1-2 weeks after petal fall.  In 2021, we hand-thinned on 5/20-5/29, about 2-3 weeks after petal fall, with an additional follow-up, corrective thinning on 6/11 and 6/15; we aimed for approximately 4-6 inches between fruits.

In both years, we noted a very heavy natural June drop of fruitlets in the weeks after bloom.  Qualitatively, the drop appeared to be higher than what we typically see in outdoor orchards.  In general, warm temperatures and low light levels favor fruit drop, and we speculate that compared to outdoors the tunnels tend to impose conditions favoring drop: the plastic covering reduces light levels and tunnel temperatures are higher than outdoor temperatures.

Heat stress damage on foliage.  There was occasional heat stress damage seen on foliage which was at a young developing stage during extremely hot weather.  The Mystery variety was particularly susceptible to foliar damage.  This damage was much more common in tunnel 1.  Fruit sunburn symptoms, discussed below, were also more pronounced in tunnel 1.  We often that note that tunnel 1 feels warmer than tunnel 2, and we presume that temperatures are higher in tunnel 1 for some or all of the following reasons:

  1. Tunnel 1’s larger width (34′ vs 24′) makes ventilation less effective
  2. Tunnel 1 is oriented east-west, in line with prevailing winds, whereas tunnel 2 is oriented north-south, which is perpendicular to prevailing winds and improves the effectiveness of ventilation through the rollup sides. 
  3. Tunnel 1 it is located about 12’ north from another tunnel (not used in this study) which reduces natural ventilation through the rollup sides. 

 

Research results and discussion:

Harvest and Yield. The table below shows total yields from both tunnels in 2020 and 2021.  The table on subsequent pages shows yield divided by variety, tunnel, and year.

 

2020

2021

Grade

Yield of Saleable Fruit from High Tunnels (Lbs)

Value of High Tunnel Fruit1

Yield of Saleable Fruit from High Tunnels (Lbs)

Value of High Tunnel Fruit1

#1

788

$2,001

3,142

$7,981

#2

451

$492

1,344

$1,465

Total, both grades

1239

$2,493

4,487

$9,446

Total, both grades, per tree

6.81

$13.70

24.6

$51.90

1Based on average prices that our farm received in 2020: $2.54/lb for #1 grade fruit, and $1.09 for #2 grade fruit.

Some general trends were noted on fruit of many varieties: 

  • Most fruit were sweeter than would be expected on same varieties grown in field. In some cases, this was accompanied by an aldehyde-type flavor which some eaters found unpleasant.  This off-flavor diminished in storage to some extent.
  • Watercore was common on some varieties
  • Some varieties showed symptoms of sunburn on fruit.  Sunburn necrosis was common in Ashmead’s Kernal, sunburn browning occurred in most varieties to some degree, and most varieties showed extremely accelerated ripening and softening on the sun-exposed sides of fruit.
  • Maturity in tunnels was hastened compared to outdoor grown apples.
  • In general, red skin color was significantly less than would be expected in field-grown apples.
  • Hudson’s Golden Gem and Suncrisp stood out among the varieties trialed for their excellent flavor and general resistance to the sunburn, watercore, and softening which were common in other varieties.
  • Yields were higher in tunnel 2, possibly because of reduced heat stress in tunnel 2.
  • Fruit sunburn, watercore, and soft flesh were more common tunnel 1 than tunnel 2.
  • No sooty blotch or flyspeck was seen despite lack of fungicide sprays.  In outdoor grown apples, we spray potassium bicarbonate (Carb-o-nator) and Bacillus mycoides isolate J. (Lifegard) regularly to control these diseases and we still find mild symptoms at harvest.
  • The overall percentage of #1 grade fruit was 64% in 2020 and 70% in 2021.  By comparison, we typically have about 75% #1 grade fruit in outdoor plantings.  We define #1 grade fruit as fruit saleable to our CSA and grocery store accounts.  We do accept significant variation in fruit size, russeting, slight deformities in fruit shape, and 1 or 2 plum curculio oviposition scars in #1 apples, but we do not accept feeding damage from adult plum curculio or other insects, watercore, bitterpit, or obviously overripe or underripe fruit. 
 

2020

2021

 

Variety

Harvest Dates

Yield Per Tree High Tunnel 1 (Lbs)

Yield Per Tree High Tunnel 2 (Lbs)

Percent of fruits which were #1 grade

Harvest Dates

Yield Per Tree High Tunnel 1 (Lbs)

Yield Per Tree High Tunnel 2 (Lbs)

Percent of fruits which were #1 grade

Notes

Ashmead's Kernal

9/22

0.3

1

n/a

9/10-9/13

1.2

1.9

50%

Heavy russeting.  Bitter pit developed in storage.  Sun-exposed fruits sometimes had black necrotic areas on exposed side of fruit (presumably sunburn necrosis).   Somewhat soft flesh.  Exceptional flavor, high sugar, moderate acid.

Golden Russet

9/22

6.1

9.2

93%

9/10-9/21

19.1

26.1

60%

Generally lacked characteristic russeting.  Sunburn and underlying soft flesh common on sun-exposed fruits – difficult to ripen fruit fully without developing soft flesh and sunburn, and therefore quality was generally fair.  Watercore common.  High sugar, moderate acid.

Mystery

10/9

5.5

15.2

66%

8/26-8/27

18.6

26.3

68%

Large size, excellent appearance.  Sunburn and underlying soft flesh common on sun-exposed fruits.  Generally soft flesh.  High sugar, low acid.  Unpopular with consumers because of soft flesh. 

Hudson's Golden Gem

10/7-10/8

0

3.2

n/a

9/10-9/18

17.5

31.6

73%

Extremely high June drop noted.  Moderate russeting.  Some watercore, but otherwise quality and flavor exceptional.  No soft flesh.  High sugar, low acid.

Calville Blanc d'Hiver

10/7-10/8

1.6

7.2

0%

8/26-8/27

6.3

11.1

0%

Tart flavor and soft texture unsaleable as #1 grade in our markets.  Blossom end russeting (“frost rings”) from frost damage before bloom in 2020.

Suncrisp

10/7-10/8

18.6

17.5

61%

9/17-9/20

35.7

80.4

81%

Large size, excellent appearance.  Slight watercore and sunburn, but generally excellent quality and flavor.  Strong tropical or banana flavor.  High sugar, moderate acid.  Popular with consumers and grocery store buyers. 

Winecrisp

10/7-10/8

3.3

6.6

74%

9/18-9/21

26.9

42.4

77%

Large size.  Red skin color did not develop well.  High sugar in 2020; but less so in 2021.  Some sunburn browning and watercore.

 

Labor Needs and Materials Costs.  The following tables shows labor time spent on the tunnel trees and costs of materials.  The total time was almost one hour per tree per year.  The most time-consuming tasks in the first two years were  trellising, training, and planting.  The time to construct the trellis and perform regular branch training was significant.  In the third year, fruit thinning, harvest, and washing became the most time-consuming tasks.

Labor time (hours) per year for various work tasks for the 182 experimental trees, not including any time related to marketing the fruit.

Work Task

2019

2020

2021

Plant fruits

43.9

0.0

0

Irrigation (apply and set up)

5.4

6.1

6.8

Mulch with hardwood bark

10.4

0.0

0

Seasonal covering/uncovering

11.6

19.0

6

Install rodent guards

2.2

0.0

4

Spray pesticide

7.4

16.0

7.4

Trellis and train trees

60.3

90.2

38.7

Weed

23.1

10.9

15.8

Thin fruits

0.0

14.4

44.4

Pick up fruit drops

0.0

3.4

6.33

Harvest

0.0

7.3

26.9

Wash fruit

0.0

4.0

16.8

Monitor temperatures and ventilate

4.0

6.3

2.4

Total hours of labor

168.1

177.7

175.6

Hours of labor per tree

0.92

0.98

0.96

 

 

Materials Costs per Tree, 2019-2021

Item

2019

2020

2021

Notes

Mulch

$4.81

 

 

$13.13 per yard

Trellis stakes

 

$7.16

 

$7.16 each

Trellis and training supplies

$0.77

$0.77

 

Close estimate of materials used: $0.32 for AgLok chain, $0.93 for 24" wire ties, $0.29 for 12.5 ga high tensile wire for trellis)

Trees

$19.84

 

 

Average price per tree of trees purchased from commercial nursery in 2019

Sprays

 

$2.05

$1.20

 

Bumblebee colonies

 

$1.61

$1.73

 Individual colonies cost $158 in 2020 and $170 in 2021

Klerks koolite plastic

 

$6.56

 

Plastic should last for three-four growing seasons

Silage tarp

 

$3.76

 

We expect that tarp will last for several growing seasons

Total cost per tree

$25.42

$21.91

$2.93

 

 

 

Based on the actual costs and labor time above, we estimated startup and annual operating costs for a hoophouse operation, as shown below:

Estimated Startup and Annual Operating Labor Needs, Minutes Per Tree.  (As described below, we have adjusted some of the figures from the actual times in our experiment.)

Work Task

Year 1

Year 2

Years 3+

Comments

Plant fruits

12

   

based on time per tree to hand-plant trees outdoors on our farm.  The actual time in our high tunnel study was slightly higher, presumably because of extra time laying out trees in our randomized planting arrangement

Irrigation (apply and set up)

2

2

2

 

Mulch with hardwood bark

0.85

0.85

0.85

every 4 years, 3.4 minutes per tree

Seasonal covering/uncovering

9

9

9

Covering with silage tarp every fall starting in year 1 (6 minutes per tree), removing silage tarp every spring (2 minutes/tree), except that every 4th year, remove clear poly in fall (2 minutes/tree) and replace in spring (10 minutes per tree)

Install rodent guards

1

0.6

0.6

Based on times in our outdoor orchard for initial installation and annual maintainence

Spray pesticide

2.5

4

4

Based on times measured in our study

Trellis and train trees

20

30

12

Based on times measured in our study

Weed

5.5

5.5

5.5

Based on times measured in our study

Thin fruits

0

5

15

Based on times measured in our study to hand-thin.  Spray thinning would reduce this considerably

Pick up fruit drops

0

1

2

Based on times measured in our study

Harvest

0

2.4

8.9

Based on times measured in our study

Wash fruit

0

1.3

5.5

Based on times measured in our study

Monitor temperatures and ventilate

1.5

1.5

1.5

Based on times measured in our study

Total

54.35

63.15

66.85

 

 

 

Estimated Startup and Annual Costs Per Tree for Materials

Item

Annual operating cost

Incurred when?

Notes

Trellis stakes

$7.16

once, in Year 1

 

Trellis and training supplies

$1.54

once, in Year 1

 

Trees

$19.84

once, in Year 1

 

Mulch

$1.20

annually, starting in Year 1

Assuming mulch is replenished every 4 years

Sprays

$1.62

annually, starting in Year 2

 

Bumblebee colonies

$1.73

annually, starting in Year 2

 

Klerks koolite plastic

$1.64

annually, starting in Year 1

Assuming 4 year lifespan

Silage tarp

$3.76

annually, starting in Year 1

Assuming 3-year lifespan

Total cost per tree, Year 1

$35.14

 

 

Total cost per tree, Years 2+

$9.95

 

 

 

 

Profitability.  The profitability of high tunnel apple cultivation depends on the specific details of a farm’s production and marketing practices.  Overall we do not feel that tunnel cultivation of apples is justifiable on our farm.  We have presented as much relevant data as possible to help other growers evaluate this question.  In our opinion, here are some of the most important considerations:

Comparison of outdoor vs high tunnel production.  For many farms, high tunnel production may represent a possible alternative or adjunct to outdoor, unprotected apple production.  In our outdoor orchard, we use a different planting density and training regimen than we used in this high tunnel study: our outdoor trees are planted at six feet apart within the row and twelve feet apart between rows.  Here are some major differences which we noted in the economics of outdoor and tunnel production:

  • In our outdoor orchard, we mulch an 8’ wide strip between rows, whereas in the high tunnels we mulched the entire area within the tunnel (to avoid the difficulty of mowing sod in the tight confines of the tunnel, particularly between the tree rows and the outside walls of the tunnel). Although a greater portion of the ground was mulched in the tunnels, the mulch degraded more slowly in the tunnel and outside: we expect we would need to replenish the mulch in the tunnels every four years, whereas outdoors we replenish the mulch annually.  The overall cost of mulch per foot of row would be similar in both systems: outdoors, we spend about $2.50 per year per tree for mulch for trees spaced 6’ apart, and in the tunnels the cost for mulch every four years would be $1.20 per year per tree for tree spaced 3’ apart.
  • Outdoors we annually spend about $2.50 per tree for year for spray materials (about $0.42 per row-foot). In the tunnels we spent about $1.62 per tree for year (about $0.54 per row foot), although we actually sprayed less – the reason for the higher cost in the tunnels was largely that we needed to mix small volumes of water to spray the tunnels and consequently waste was a much higher portion of the total cost.
  • Outdoors, mature trees at 6’ spacing require almost two hours of labor per year (ignoring marketing time and overhead tasks such as accounting, equipment maintenance, etc). The third year high tunnel trees, at 3’ spacing, required slightly more than one hour per tree at 3’ spacing, so the overall labor requirement per row foot was similar. 
  • Cost of silage tarp and clear polyethylene, both of which need to be replaced every few years, add a substantial operating cost for the lifetime of the planting - $5.40 per tree for year.
  • It is somewhat difficult to compare yields between the high tunnel plantings and our outdoor orchards. The tunnels were planted at a higher density (3’ spacing in the tunnels vs 6’ spacing outdoors) and we fruited the tunnels in the second year, whereas we usually wait until the third year to fruit outdoor plantings.  In addition, most of the varieties grown in the tunnels are not in our outdoor orchards.  The third-year yield in the tunnels averaged almost 25 lbs per tree.  For an equal yield per row-foot, outdoor orchards would need to produce 50 lbs per tree.  We rarely obtain a 50 lbs/tree yield in 3rd year trees outdoors, but it is common in 4th or 5th year trees.  Overall, we would say that the tunnel plantings produced more in the early years than is normal in our outdoor orchards, likely because of the higher planting density.  However there is no particular evidence that the yield of mature plantings would be higher in the tunnel. 

Cost of the high tunnel structure and materialsThe two tunnels used in our study each cost about $10,000 in materials for construction, plus about 180 hours in labor time.  On our farm, the materials cost of the two tunnels was covered by funding from the USDA-Natural Resource Conservation Service EQIP program.  In addition both tunnels were originally constructed for use in growing vegetables.  When we transitioned our farm from vegetable to fruit production we were looking for a new use for the tunnels.  Growers who are considering constructing tunnels specifically for fruit production would need to justify the cost of the tunnels.  A rough analysis suggests that this would be very difficult – the figures in the table below suggest it would take over 10 years to repay the cost of the tunnel, even with a better mix of varieties than we grew for this study.  However, these figures are highly dependent on yields and costs, which depend on variety selection, insect control, labor efficiency and myriad other factors specific to individual farms. 

 

 

Hypothetical annual costs and returns from high tunnel apple planting, including costs of tunnel construction

Year

Cost of Materials1

Labour Hours2

Cost of Labor ($18/hour)

Overhead / Marketing Costs3

Sales4

Total Net Return5

06

$10,000

180

$3,240

$0

$0

($13,240)

1

$3,514

91

$1,631

$1,286

$0

($19,671)

2

$995

105

$1,895

$722

$2,613

($20,670)

3

$995

111

$2,006

$750

$6,533

($17,888)

4

$995

111

$2,006

$750

$6,533

($15,106)

5

$995

111

$2,006

$750

$6,533

($12,324)

6

$995

111

$2,006

$750

$6,533

($9,542)

7

$995

111

$2,006

$750

$6,533

($6,760)

8

$995

111

$2,006

$750

$6,533

($3,978)

9

$995

111

$2,006

$750

$6,533

($1,196)

10

$995

111

$2,006

$750

$6,533

$1,586

11

$995

111

$2,006

$750

$6,533

$4,367

12

$995

111

$2,006

$750

$6,533

$7,149

13

$995

111

$2,006

$750

$6,533

$9,931

14

$995

111

$2,006

$750

$6,533

$12,713

1Based on a $10,000 cost for the high tunnel materials, plus startup costs of $35.14 per tree and annual operating costs of $9.95 per tree.  All figures assume 100 trees per tunnel (our tunnels held 99 and 98 trees each)
2180 hours for tunnel construction, 54.25 minutes per tree in year 1, 63.15 in year 2, and 66.85 in years 3+
3All of the costs and labor times presented previously in this publication ignore overhead and marketing costs, such as cost of purchasing and maintaining tractors, sprayers, and delivery vehicles, fuel, tax preparation, accounting and tax preparation, and farm planning.  In reality, these costs are very substantial.  In the table above, we have somewhat arbitrarily set them at 25% of the other costs.  Farms should substitute figures relevant to their own operation – but don’t ignore these very large and important costs.
4Sales based on a yield of 12 lbs per tree in year 2, and 30 lbs per tree in subsequent years, and 75% #1 grade apples.  These figures are higher than what we observed in our study but we feel they are reasonably attainable with good variety selection.  Sales were calculated using the average prices which we received on our farm in 2020: $2.54/lb for #1 grade apples and $1.09 for #2 grade apples.
5Total net return ignores inflation, loan interest, and the opportunity cost incurred by not investing this money in other ways. 
6Year 0 represents the cost of high tunnel construction.

Labor utilization.  We found that the high tunnels provided a place to work and utilize available labor during rainy weather in spring and summer, when it was difficult or impossible to work outside. 

Scale.  Using large field tunnels such as those manufactured by Haygrove might reduce the costs per square foot of constructing and maintaining the tunnel structures and improve the profitability of tunnel apple cultivation.

Disease and pest pressure.  As expected, diseases other than powdery mildew were very rare in the tunnels.  In general, insect pest levels were not much reduced in the tunnels compared to outdoor orchards.  The reduced disease levels might allow organic cultivation of disease-susceptible varieties which are difficult or impossible to grow organically outdoors, although a full regimen of insect sprays would likely still be required inside the tunnels.  Growers need to consider whether those varieties command a market price which would justify the costs of tunnel culture.  Also consider whether the reduced disease pressure in tunnels will actually result in reduced spray costs.  On our farm, the tunnels represent a small area of land relative to our outdoor orchards.  It would be most convenient to spray the tunnels with the same spray mixtures as used outdoors, but this would eliminate any possible savings in spray material costs.  Also note that sulfur sprays, commonly used for control of apple scab and other disease in organic orchards, are destructive to greenhouse polyethylene.

Environmental impacts.  High tunnel production may be environmentally beneficial if it reduces the amount of pesticide inputs and/or increases local organic apple production and reduces the volume of organic apples which are imported into the north central region from Washington state.  However, high tunnel production has clear negative impacts in its reliance on greenhouse plastic and silage tarps, which are energetically costly to produce and can be difficult to recycle. 

High tunnel environment.  Although we did not measure environmental conditions inside our tunnels, there are clearly important differences in the environment between tunnels and outdoors.  In the tunnels, rainfall is absent, daytime temperatures are higher, light levels are lower, humidity is higher, and wind is less.  Although the lack of rainfall reduces most diseases, it’s important to consider other factors:

  • Higher temperatures can damage leaves and fruit.
  • Higher temperatures and lower light levels in June may increase self-thinning of fruitlets.
  • The different light regime inside tunnels appears to reduce red coloring in fruit.
  • The tunnel environment appeared to promote watercore, fruit flesh softening, and early fruit maturation.
  • Tunnels may provide little or no protection from freezing temperatures before and during spring bloom. A backup heat source might be a wise investment.

Variety selection.  We observed enormous differences between varieties in our study in their yield and susceptibility to sunburn and other fruit defects.  Selection of heat-tolerant, high-yielding varieties would be essential to profitable high tunnel apple cultivation.  In our study, Suncrisp and Winecrisp were the highest yielding varieties, and Suncrisp and Hudson’s Golden Gem produced the highest quality fruit with the lowest incidence of watercore, fruit softening, sunburn and other defects.

High tunnel size and orientation.  As discussed previously, tunnel 2 had higher yields and fewer heat-related fruit defects compared to tunnel 1.  We recommend siting and designing tunnels for maximum ventilation.

Participation Summary
1 Farmer participating in research

Educational & Outreach Activities

2 Consultations
1 Curricula, factsheets or educational tools
4 Published press articles, newsletters
1 Tours
2 Webinars / talks / presentations
1 Workshop field days

Participation Summary:

120 Farmers
40 Ag professionals participated
Education/outreach description:

We hosted a field day at our farm, sponsored by CRAFT Angelic Learning Center, on July 14, 2020.  There were 18 attendees.  Although it was early in this project, we used the opportunity to speak about the progress of this project and distributed a handout describing our experiment and results to date: Field Day Handout July 2020.  Ten attendees provided their email addresses and asked to receive a final summary of the project.

On March 16, 2021, we consulted via phone with John Newton, Pleasant Hope, MO about this plans to grow high tunnel apples.

On June 6, 2021, we gave a tour of our high tunnel apple planting to Hannah Frank and Justin from Rue de Bungaloo Farm, Athens, Wisconsin.

In December 2021, we presented a research poster at the Great Lakes Fruit and Vegetable Expo in Grand Rapids, MI.    This event is typically attended by over 3600 farmers and agriculture professionals.

In January we posted a detailed summary of our project results on our website.  We emailed this summary to the Practical Farmers of Iowa horticulture email list and the Organic Fruit Growers Association email list serve.  We received six emails from farmers and researchers with comments or questions on our project.

In January 2021, we submitted press releases to Country Today and Agri-View (both state or regional farming newspapers) as well as American Fruit Grower, and Fruit Growers News (national publications for fruit growers).  Agri-View  and Fruit Growers News have published articles about this project in recent online and print editions.  Apple High Tunnel Press Release Fruit Publications and Apple High Tunnel Press Release Regional Farming Papers

In addition, we have submitted articles summarizing our project to the Wisconsin Fruit News, published by University of Wisconsin-Extension, and Just Picked, the newsletter of the Organic Fruit Growers Association.  The editors have agreed to publish these articles later in 2022.

Learning Outcomes

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

In brief, we learned that it's possible to grow disease-free organic apples inside high tunnels.  Although the trees grow well, fruit often suffer from heat-related defects such as sunburn.  Varieties differ hugely in yield and susceptibility to heat damage.  Currently we cannot recommend high tunnel cultivation of apples because of the heat damage and costs of constructing and maintaining the tunnels.  However, it possible that with proper variety selection and measures to reduce summer high temperatures inside the tunnels, that this could be a viable method for growing organic apples.

Project Outcomes

5 Farmers changed or adopted a practice

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.