Fruit & Vegetable Magazine

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Raspberry production under cover

November 30, 1999  By Dan Woolley

Many growers are adopting production using poly tunnels without enough information about the types of crops they should be growing according to Dr. Jean-Pierre Prive.

Many growers are adopting production using poly tunnels without enough information about the types of crops they should be growing according to Dr. Jean-Pierre Prive.

The Agriculture and Agri-Food Canada research scientist from Bouctouche, N.B., has been conducting research trials on rain shelters and reflective cloths for raspberry production. His goal is to “try to make production systems more ecologically sound.”


Dr. Prive notes Canadian annual red raspberry production, worth $35 million, totals 12 million kilograms with B.C. accounting for 86 per cent of Canadian production and Atlantic Canada just more than one per cent.

The average yearly rainfall in Abbotsford, B.C., is 62 inches while in Bouctouche the average annual rainfall is 45 inches. Despite this difference, the timing of Bouctouche precipitation results in more rain during the fruit-bearing season, creating increased disease pressure on the berry crop, says Dr. Prive.

He adds that the climate is also getting warmer in all four seasons – perhaps more so in the winter than the summer – resulting in more precipitation and a longer growing season with more frost-free days. As a result, plants need more energy to grow under these conditions because they respire more and pests, insects and disease will tend to increase, says Dr. Prive, using the European corn borer as an example. For every centigrade degree increase in the temperature, the pest will move 500 kilometres further north.

To help combat these issues, growers can consider using a poly cover or rain canopy, says Dr. Prive. The cover can be used to prevent water falling on plants and propagating disease. Dr. Prive uses a Belgian-designed rain shelter in his research projects that can be placed over a new or existing planting and opened to admit sunlight when “sunlight is at a premium.”

He also uses Extenday reflective coverings under the rain shelter, tied to the trellis. Both the shelter and ground cover work together to modify the environmental components of temperature, moisture and humidity to impact productivity, Dr. Prive says.

Under Maritime conditions, the poly cover will not extend the growing and fruiting season but the Extenday row cover creates a significant difference on soil temperature and moisture, he says, adding he has seen no negative effect on the rate of photosynthesis with the rain shelter. Dr. Prive has also observed much higher yields with the Extenday row covering and the poly covers used alone and in combination. With just the Extenday row covering, there was an increase in marketable fruit of 10 per cent while the use of the poly cover alone resulted in a 90 per cent increase.

The poly cover also helps with storage issues says Dr. Prive, adding that when there is no rain shelter and no cold storage used, there is a 50 per cent spoilage rate in the berries two days after harvest. With berries grown under the poly cover, three days of storage were possible before 50 per cent spoilage rates occurred, he says.

The poly cover also helps with cane growth and when combined with Extenday row covers, adds more dry weight in fruit and canes, says Dr. Prive. As a result, he suggests growers may have to develop ways of increasing the height of their trellises to accommodate the added fruit mass. And, while the canopies should result in less disease and a reduced need for fungicide applications, Dr. Prive says he observed an increase in the presence of ground beetles (carabidae) because of the use of Extenday row covers.

Dr. Prive and his research colleagues at AAFC Bouctouche are now calculating an economic analysis of their research results.

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