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Organic Agriculture Centre of Canada

With more and more Canadians looking for local and organic fruits, it's up to Canadian farmers to increase the supply.聽 The challenge lies in encouraging more Canadian growers to make the transition to organic.聽 This switch requires a major change in how they manage their crops, because today's conventional fruit production is highly dependent on chemical inputs to control insects, diseases and weeds.聽 Canadian researchers are helping farmers find ways to manage orchards without relying on conventional inputs.

One such project looked at how cellulose sheeting can be used in apple orchards to control not just one problem, but three.聽 Diane Benoit of the Horticultural Research and Development Centre in Quebec, along with her team of researchers, spent four years tracking the effects of a mulch of special kraft paper on weeds and two pests, the apple sawfly and the plum curculio (a beetle). The results of this study, 鈥溾�� were published in a 2006 edition of Crop Protection.

The apple sawfly was introduced from Europe and is now found throughout eastern Canada, while the plum curculio is native to North America.聽 Both insects spend part of their life cycle as larvae in fruitlets.聽 As a result, the fruit drops to the ground.聽 The larvae then pupate in the ground, before emerging as adults and laying eggs on the trees.聽 Here the two insects differ slightly 鈥� the plum curculio overwinters as an adult, while the apple sawfly remains as a pupae in the soil and emerges as an adult the following spring.

Weeds are another challenge for organic growers, as they compete with the trees for water and nutrients.聽 In conventional orchards, farmers typically use herbicides to control weeds.聽 However, this management tool is not available to organic producers, so they must find other solutions.

There may be a way to solve all three problems.聽 The trick is to prevent the weeds from getting out of the soil and the insects from getting into it.聽 The solution proposed by Benoit and her team is to cover the orchard floor with thick cellulose sheets.聽 And it works.聽

The solution lies in a special kind of cellulose sheet.聽 The 15mm thick sheet consists of kraft paper, sandwiched between biodegradable layers of polylactic acid, with one side clear and the other dyed black.聽 The researchers found that this mulch reduced the emergence of plum curculios by 47% to 100%, three years out of four.聽 The emergence of apple sawfly adults was reduced by 60 to 95%, two years out of four.

In the case of weeds, the sheets were also helpful.聽 No weeds were found on the newly replaced mulch sheets in summer and fall.聽 And the amount of weed seeds present in the soil was also reduced.

Such a simple solution cannot be without limitations.聽 One such difficulty with the sheets is that they biodegrade within one year, and so they must be replaced regularly.聽 Furthermore, the researchers also found that the sheets degraded faster where fruits, leaves or moisture accumulated on them.聽 This allowed weeds to become established by the following spring.聽 And it allowed the insects to pupate 鈥� either in the material that accumulated on the sheets or in the soil where the sheets had degraded.

The team does have an idea for how to deal with these problems 鈥� remove the fallen fruit in early July.聽 In small orchards this would generally not be a problem, but in large orchards the task would require mechanization to be feasible.

But the efforts may well be worth it.聽 The sheets appear to be so effective that using them for a few years could nearly eradicate the problem insects, at least temporarily.聽 Once the insect and weed populations have been reduced, the grower could take a break from using the mulch for a few years, until the insects become a problem again.聽

Unfortunately, the cellulose sheets used in the experiment are not commercially available.聽 The company that supplied them has not developed the product further.聽 But, farmers can still apply the results of the study.聽 For example, similar paper-based mulches may be available on the market.聽 And, other types of mulch may also be worth experimenting with. The key is to disrupt the life cycle of both the insects and the weeds.聽 Mulches are just one more tool in the organic grower's tool kit!

This article was written by Kristine Hammel on behalf of the OACC with funding provided by Canada鈥檚 Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).聽 The Organic Science Cluster is a collaborative effort led jointly by the OACC, the and industry partners. For more information: oacc@dal.ca or 902-893-7256.

Posted July 2011