Organic Strawberries

By Dan Wooley, August 22, 2006

The public’s fears about pest management practices create an opportunity for organic fruit growers, said John Lewis.

The Agra Point International berry fruit specialist, however, cautioned producers attending his presentation on organic strawberry production at Agrifest, researchers and the agricultural community are still scrambling to come up with a viable organic production system.

Lewis commented: "I think we are very close; but it hasn’t been yet and demonstrated."

Strawberries are very hard to grow organically, he admitted, mainly, because of the crop’s "broad pest profile."

The real challenge this year has been the 10-fold multiplication of fruit rot in organic berries because fungicides could not be used, Lewis said. "You have to have a pest control strategy.....without it you will lose money and fail."

Normally, powdery mildew isn’t a problem in Nova Scotia; but it was this year due to wet conditions and high humidity, he noted.

Sulphur powder spray can be applied as a mildew control, although it is hard on the plants.

Lewis also observed weeds can be a real problem in organic berry production for which he recommended the use of lots of green manure in a crop rotation to curb weed growth before planting strawberries.

The grower should till the green manure into the future berry bed, before weeds have a chance to seed, said Lewis, recommending also lots of cover cropping for two to three years before planting the strawberries.

He recommended, as well, raising organic strawberries under black plastic and having a control strategy for diseases such as botrytis.

When it rains botrytis spores are splashed from the soil onto the plants, but by growing plants on raised plastic-covered beds they will be exposed to air and breezes and dry off quickly, he said.

Lewis estimated the plastic will last three years, with the only problem being birds punching holes in it to search for grubs in the bed.

The plastic and beds can all be laid and made in one operation, with trickle irrigation being first laid down two to three inches deep down the centre of the bed, he said.

Although strawberries do not have big nutrient needs, observed Lewis; "my experience is you should really think about organic compost."

Fish fertilizers in solution can also be applied to the beds through the irrigation lines or applied to the plant foliage.

Before planting the bed, the growers should soil test for essential nutrients and the soil amended, if required, by a applications of rock phosphate, limestone or gypsum.

Phosphorus is also very important, he noted, for good root development and dipping the plants roots into a compost tea which will help the roots access phosphorus for the plant.

Root diseases such as red stele can also be prevented by bio-active beneficial fungi from a compost tea, said Lewis. "We made a compost tea and dipped the roots into it to innoculate the plant to create a good biology environment around the plant root so that when it is planted you do not see black root rot."

A lot of organic growing is preventive, he said. "You have to know what you are doing."

There are new biological disease controls such as trichoderma. It colonizes the leaves of the plant creating a good control environment to prevent the development of botrytis.

As for insect control, Lewis admitted there is a real problem with strawberry harvest weevil larvae feeding on plant roots. Until 10 years ago it was a minor problem, but with the recent mild winters the larvae are now over-wintering and "we are seeing pests that are now major, that were minor 15 - 20-years ago."

There is a beneficial nematode that can be applied at cost of $200 an acre through a trickle irrigation system, he said. "If you lose half your crop, or all of it; you can justify the cost of this control."

There are three or four commercially available predator mites and midges that can be very effective seasonal control on mites, a major pest, he said.

Organic agriculture, explained Lewis, is about fostering a very healthy, biological system to achieving a balance in controlling pests.

He declared: "Five years ago I would have tried to talk an organic rower out of strawberries. I am confident now I could give him a program."

Lewis conceded, nevertheless, most consumers are not yet prepared to pay a premium price for organic fruit.

He suggested that organic strawberry producers plant early season varieties that get the best prices at the start of the annual harvest and avoid high pest pressure late in the season.

Row covering will also advance the season by two - three weeks, Lewis said. "There is no reason you couldn’t be getting 350 - 400 quarts (per acre) by the beginning of June."

Row covering is the most expensive part of the growing system, he observed, but it advances the season and it keep pests out of the strawberries bed.

Because of disease pressure from crown rot and phytophera, Lewis felt Nova Scotia growers might have a competitive niche in the North American market. "We have a much better chance of growing organic strawberries here than in Florida. We can produce clean plants: They can’t."


OACC gratefully acknowledges the author for permission to post this article on our website.


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