Berry Growers: To Tunnel or Not to Tunnel?

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Berries and raspberries are grown in tunnels around the world, but are they right for B.C. growers?

Tunnels are used in many countries around the world to grow strawberries and raspberries. These protected environments have benefits, but certainly have a price tag associate with them. Kathy Demchak from the Department of Plant Science at Penn State University helps growers understand the risks and rewards inherent in tunnel berry-growing.

Types of tunnels

There are a number of shapes, sizes and configurations for berry tunnels. High tunnels come in single, or multi-bay, where as low tunnels are always single-bay, or more accurately, single bed. Single-bay tunnels, preferred by smaller crop growers, are typically smaller than the structures used in multi-bay setups.

“Multi-bay tunnels are used to cover large areas,” Demchak explains.

Multi-bay structures are typically bays of 200 to 300 feet long and 24 feet wide that are then attached or tied together providing more structural integrity. Like single-bay tunnels, the hoop frames are covered with six to eight mil clear plastic that will generally last about three seasons; proper installation being the prime indicator for longer life. Snow loads may require taking the plastic down but in some climates tunnels can stay in place year-round, particularly for single-bay tunnels.

Low tunnels are typically two feet or shorter in height and are a lighter weight plastic – about 1.5 mil – and generally last one season. These plastic covers span a single row and unlike the high tunnels, work is done from outside the structure, and there is protection from the elements only for the plants, not for workers.

Survey of strawberry growers

In 2010 and 2011, a high tunnel survey was done among three grower groups (potential high-tunnel berry growers, current high-tunnel berry growers and former high tunnel berry growers), all of which were experienced berry grower groups. Within the survey, June berries were most likely to be grown in a single-bay tunnel while everbearing berries were split evenly between single and multi-bay tunnels.

“Fruit appearance was the number one reason,” says Demchak of why growers were using tunnels in both everbearing and June bearing berries.

In June bearing, growers’ second reason for using tunnels was the ability to harvest while it was raining and the second reason for everbearing was increased yield.

Will strawberry growers who tried high-tunnels continue?

The June bearing growers found that prices and yields didn’t justify the expense of tunnels, but in everbearing, many planned to increase their tunneled acreage.

A number of benefits emerged from the survey.

“Tunnels do provide some degree of control over the environment,” notes Demchak.

While the high tunnels cost more than their low-tunnel cousins, they allow the ability to work within the structure at any time. This controlled environment also includes the ability to lengthen the harvest season, increase yields, create a higher percentage of marketable fruit and allow for longer shelf life of the everbearing berries.

Most growers reported payback in two to three years when using high tunnels for growing. Demchak also said going organic and pesticide-free growing is easier in tunnels, but integrated pest management systems would be a good addition.

On the downside, strawberry roots were exposed to higher levels of salt, perhaps due to the lack of snow or rain water leaching it away.

“You won’t want to grow strawberries [in a tunnel] after something like tomatoes,” she says. “We do need to work out the production systems.”

Demchak feels that excess salinity could potentially be leached out of tunnel areas through increased irrigation.

Other issues noted by growers were an increase in management time (to control temperatures but as Demchak pointed out, this is quite minimal) and plastic waste concerns, but plastics are seeing new options coming to market soon that deal with waste issues.

“Pay off depends on crop management skills, Demchak says. “There is a cost to the constant maintenance and temperature management.”

Spider mites were also mentioned as an issue for some growers.

“Our recommendation for that is to release predatory mites when first seen and just keep scouting,” she says.

Despite the upside, some growers still felt the benefits didn’t justify the costs and both groups which had grown berries had some growers switch to using the tunnels for higher value crops such as tomatoes. While the off-season berries were a plus, finding a market for them proved to be somewhat of a challenge as consumers weren’t expecting locally-grown berries at that time. If growers can achieve higher selling prices and markets for off-season berries, they may well find that the costs of tunnels are worthwhile.

So are low tunnels a better option?

Low tunnels weren’t surveyed with strawberry growers, but the ability to work in the high-tunnel structure may outweigh the higher costs of the structure over the cheaper low tunnels.

Tunnels for raspberries

Raspberry growers were surveyed about their use of high tunnels and reasons for using the structures included increased yield, improved appearance and ability to harvest in the rain. While the tunnels delivered a larger berry and fungicide-free fruit, spotted wing drosophila (SWD) impacted longer shelf life and pesticide-free qualities.

Very few raspberry growers discontinued growing raspberries in tunnels or planned to decrease their tunnel acreage.

“The number of growers planning to increase their acreage significantly outpaced those planning to decrease acreage,” Demchak says.

Results of the raspberry growing season

In Philadelphia, growers saw two to four times increase in yield. “When you’ve got them in a tunnel, you’ve really got them in an optimal growing season for 50 per cent of the time,” Demchak notes. “We get a higher yield that first year and it will go up from there.”

Learning kept pace with the plant growth. Plants grow faster and larger in the high-tunnel.

“Keep a minimum of seven feet between rows,” notes Demchak. “Plants will get away from you. We use a simple support trellis or like a V row.”

Water quality becomes a larger issue in a controlled environment.

“We recommend to growers that they test their water source,” she says, and adds that tissue testing each year is important to see if fertilizer rates are right.

There was also a major decrease in diseases in the tunnel as well as harvests occurring two to three weeks earlier.

“We’re finding generally if it [a variety] works good in the field, it’s good for a tunnel in your area,” she notes. “We never had anything do worse in a tunnel.”

Some growers were concerned about pollination but Demchak found that bumblebees liked the tunnels. Honeybees however did seem to get confused and sometimes caught in the peak of the structure. She recommends providing nests for both mason and bumblebees within the high-tunnel structures.