Producing Pesticide-Free Apples: Canadian Researchers Are Tackling This Daunting Challenge

Unrealistic. Out of touch. Impossible. These are words that are often heard when the question of pesticide-free agriculture is raised. Especially when it comes to apples, since many dozens of pests and diseases can (and will!) plague our orchards as soon as applications of phytosanitary products cease. Even in organic production, pesticides are needed to protect the apples, although synthetic pesticides are prohibited of course.

And yet, a block of a few thousand apples trees in the Mont-Saint-Bruno orchard, south of Montreal, has been producing magnificent and delicious Honeycrisp apples for more than six years now, with no pesticide applications. By what miracle? 

The apple trees there are growing in a complete pest exclusion system, developed by Gérald Chouinard and his team at the Research and Development Institute for the Agri-Environment (IRDA). Inspired by the systems developed in Europe for use against the codling moth, the researcher and his colleagues proposed a similar system adapted to manage the range of pests encountered in Canadian apple orchards. They then studied the effects of the system, which consists of nets deployed over the crop row by row. Their studies focused on parameters such as tree health, fruit quality, and, protection against damage caused by insects. As well, they analyzed protection against damage caused by diseases, birds, hail and any other possible form of attack on foliage and fruit. 

The findings were a surprise. After all these years, not only did the nets protect apples from attacks by all the major apple tree pests in Eastern Canada (plum curculio, apple maggot, tarnished plant bug, codling moth), but they also afforded protection against several secondary pests (leafhopper, scarab beetle, apple bug – the latter a family that includes the dreaded brown marmorated stink bug). In addition, the incidence of a number of diseases (scab, fly speck, sooty blotch, rust) was also reduced. The system also provided effective protection against hail with no significant effects on apple tree health (photosynthesis) or fruit quality (colour, size, firmness, sugar content). Moreover, contrary to widespread preconceptions, neither temperature nor relative humidity was affected by the presence of the netting, apart from a 1°C increase in temperature for one or two hours when the sun was at its zenith. 

Naturally, the researchers also encountered a few difficulties along the way. The structures supporting the nets were damaged by violent winds during the first year, but more resistant materials used thereafter held up well in subsequent weather events. To allow bee pollination, the nets needed to be opened for two to three days during bloom. This was a laborious operation given that the system was not mechanized. On the other hand, the nets did limit over-pollination, which reduced the cost of fruit thinning operations. Lastly, a secondary insect pest (obliquebanded leafroller) ran rampant for a few years, and aphids, relatively unaffected by the nets, were an occasional problem as well.