Sep 19, 2016
Three-season high tunnel fruit production gains steam

Beginning in 2010, organic and conventional production of red raspberries, sweet cherries and blackberries have been studied by Michigan State University (MSU) researchers under an acre of multiple bay high tunnels (Haygrove Tunnels).

“High tunnels offer a means of manipulating the environment around crop plants, resulting in many changes in plant growth and prevalence of insects and plant pathogens,” said Eric Hanson, a professor in MSU’s Department of Horticulture. “Some changes are particularly beneficial in organic production systems.”

A high tunnel fruit production tour was conducted in July at the Horticulture Teaching and Research Center in Holt, Michigan.

Rufus Isaacs and Heather Leach of MSU Entomology discussed insect management approaches. Annemiek Schilder of MSU Plant, Soil and Microbial Sciences addressed disease challenges, and Hanson, Greg Lang and Josh Moses of MSU Horticulture reviewed production systems and tunnel management. MSU organic agriculture outreach specialist Vicki Morrone reviewed general organic production topics.

Lang noted the sweet cherry trials are no longer certified organic due to controls that needed to be used to maintain the plantings.

Some of the current research goals at the site are to: determine the benefits of tunnels for double cropping raspberries; assess the benefits of exclusion netting and harvest frequency for managing spotted wing drosophila populations in raspberries; determine the impact of tunnels on pesticide efficacy; investigate using a rotating cross arm trellis system for consistent production of blackberries; and determine the best sweet cherry varieties and training systems for tunnel environments.

“There are many types and sizes of high tunnels, including very small ones and medium size that are stand-alone structures,” Hanson told attendees during the tour of the tunnels housed on five acres.

Eric Hanson of Michigan State describes high tunnel fruit production strategies.
Eric Hanson of Michigan State describes high tunnel fruit production strategies.

“These are multiple bay tunnels because they’re connected to each other,” he said. “Also, think of them in Michigan as three-season tunnels because they’re not engineered to hold snow. If it snows when the plastic’s on, you could be in trouble.”

He said the tunnels are covered with plastic from late April or early May, extending through October.

“We get the plastic off and it sits in a trough in between the tunnels and you bundle it up for the winter. And then we pull it out in the spring and put it back on.”

The tunnels MSU is using cost about $35,000 for about an acre of coverage. The plastic costs about $7,500 to cover the tunnels and lasts about four years.

“So in the long run the plastic is almost as expensive as the tunnel if you annualize the cost of the structure that might last 15 years or so,” Hanson said. “Replacing that plastic every four years is a big investment.”

Hanson described the research work that has included growing raspberries starting at the beginning of the project four years ago.

“Now we’ve moved into a few other things with raspberries, including double cropping. That fruit on the first year canes starts fruiting in August-September on top of the one-year-old cane. You can cut all the canes down to the ground each spring, grow the canes and only have fruit in the fall – or keep some of the canes and overwinter them. If you do that, then they will fruit in the middle of summer, so that’s the double cropping.

“You get fruit on the two-year-old canes in July and then you get fruit on the one-year-old canes in August, September, October,” Hanson said.

Another project involves looking at different kinds of plastics.

“Plastics manufacturers are working real hard at developing different properties to the films that you cover tunnels with,” Hanson said. “They call them sometimes smart plastics because they are able to screen out certain wavelengths of light.

“One of the things we’re looking at is plastics that will allow all of the ultraviolet radiation through, and comparing that to plastics that will allow just portions of the ultraviolet radiation through,” he said. “The reason that’s potentially important is bugs navigate with ultraviolet radiation. High levels of the shorter wavelength radiation actually kills fungal spores. So it might provide some disease control.”

Another technique Hanson is looking at is a swing arm trellis on blackberries, planted last year.

“Some of the best and most beautiful tasting things aren’t quite hardy enough
to grow in Michigan, such as Columbia Star and Obsidian. They are developed in Oregon and if they’re exposed to Michigan winter, they’ll be dead to the ground every year. If they’re on this swing arm trellis, we can lay them on the ground and cover them up with a row cover during the winter and get them through the winter.”

High tunnel benefits

According to information provided by MSU, high tunnels offer several potential advantages for production of raspberries in humid regions such as the Midwest, including:

• Improved plant vigor and yields.

• Extended harvest and marketing season.

• Improved berry quality.

• Reduced damage from several pests and diseases.

For organic producers, these benefits may be particularly valuable since pesticide options are limited. MSU offers a bulletin that integrates knowledge on conventional culture of high tunnel raspberries with information collected from the MSU organic high tunnel research project.

The project tested cultural methods for organic production of fruits under high tunnels. The high tunnel research included nine, 26-by-200-foot, multi-bay tunnels from Haygrove Tunnels constructed on a sandy loam soil.

Three bays were each planted with raspberries, sweet cherries and mixed raspberry and sweet cherry plantings. The bulletin provides guidance for growers interested in high tunnel production of organic raspberries, though the information is of value to non-organic growers as well. Topics include:

Site selection. Sandy loam or loamy sand soils are best because they provide good drainage. Poor drainage promotes root rot in brambles. With loam and clay loam soils, modify drainage by using raised beds and installing drain tiles under sidewalls. Flooding and erosion can also occur since during rainstorms, large volumes of water run off the tunnel sides. If soil does not drain adequately, subsurface drain tile should be installed along each side of the tunnel to help direct rain water away from the plants. Tiling is especially important if the soil has a high percentage of clay or if the slope is negative from surrounding areas. The year before planting, be sure to test the soil and adjust the pH to 6.0 to 6.5 with lime or sulphur additions. Soil preparation should also include planting cover crops for a year prior to planting brambles to reduce weeds and improve soil quality. Short-lived cover crops such as buckwheat and oats work well as they can be grown and incorporated twice in one season to add organic matter and suppress weeds. Sorghum-sudangrass is another good option for smothering weeds and producing large quantities of organic matter. Sites may also benefit from applications of 1 to 2 tons of manure per acre the year prior to planting canes.

Tunnel and plastic types. Raspberries grow well in multi-bay tunnels and stand- alone tunnels. Multiple bay tunnels consist of interconnected bays and are relatively inexpensive per area covered, but they
can be damaged by snow and need to be uncovered during the winter in snow- prone areas. Plastic needs to be installed and removed annually, which can tear the plastic and is a high labor cost. Plastic should be installed after the threat of snow in the spring and removed before the first autumn snowfall.

Tunnel orientation. North-south orientated tunnels provide the most uniform light distribution. However, multiple-bay tunnels are subject to wind damage. Since wind direction during summer storms in Michigan is usually from the west, orienting tunnels east-west may reduce risks since wind can blow through the tunnels. Choice of orientation is site- specific. If the site is protected by hills or trees, wind hazard is less important. Tunnels oriented up a gentle slope will help dissipate heat by acting like a chimney.

Varieties. Desired varieties have high yields and fruit quality, some resistance to pests and diseases, and ripen at the desired marketing time. Primocane-fruiting varieties produce fruit on one-year-old canes in the late summer and fall. Floricane-fruiting varieties only fruit on two-year-old canes in June and July. In previous high tunnel studies, researchers observed that the relative qualities of raspberry varieties in the open field tend to be similar in high tunnels.

Researchers tested three newer primocane- fruiting varieties in this study: Joan J, Himbo Top and Polka. Yields from these varieties were similar, ranging from 6,500 to 11,500 pounds per acre. Himbo Top is vigorous and produces large, lighter red berries that are somewhat soft. Joan J produces firmer berries with an excellent flavor, but they are a darker red that some customers perceive
as overripe. Polka berries also are very tasty and firm with a shiny, bright skin, but Polka is very susceptible to potato leafhopper damage. Joan J and Polka are early season primocane f inue one to two weeks later than open field harvest.

Stand-alone high tunnels vary in size and design, but are generally smaller and more costly per square foot. Many can withstand snow, stay covered all year and be tightly enclosed so that harvest times can be manipulated more than with multiple-bay tunnels. Stand-alone tunnels can also protect raspberry canes from winter injury.

Plastic coverings vary in light transmittance. Researchers used Luminence THB plastic, which reduces tunnel temperatures by screening infrared light and also diffuses (scatters) light. This or similar films will work well for raspberries since optimum summer temperatures are likely below 80° Fahrenheit (26° Celsius). Standard greenhouse films that do not remove infrared light allow more direct light and thus increase summer temperatures. With any plastic film, tunnels need to be vented during warm weather.

Costs and potential returns have been compiled in a spread sheet. Email Eric Hanson at [email protected] to request a copy.

Capital investments to establish one acre of raspberries under tunnels were paid off in the second year and annual net profit after the first year was estimated to be about $12,000.

“The primary drawback to organic raspberry production under tunnels at this point is the challenge to manage spotted wing drosophila with organic-approved practices,” Isaacs said. “We do not have a means of consistently controlling this pest.”

Gary Pullano, associate editor

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