Environmental Sustainability in Practice

Pesticides and Pesticide Resistance

Insects, weeds and other ‘pests’ can wreak havoc on agricultural crops by reducing the quality and the quantity of a crop that is produced. Weeds compete with the crop for water, sunlight and nutrients needed for plant growth, and they grow very quickly. Weeds can include plants not planted by the farmer (like dandelions in a suburban lawn) or they can also be seeds from the previous year’s crop that grow together with the crop that was planted, called volunteers (for example, if you have ever driven by a field and seen a few lonely cornstalks growing in a field of wheat, these are volunteers). Insects feed on the plant material of the crop, including the leaves, stem and/or ‘fruit’ produced by the plant.

Of course, farmers want to minimize the impacts these pests have on their crops. In modern agriculture, there are several ways in which these impacts can be minimized, including making planning and management decisions that reduce the potential for pests to cause damage. However, many farmers (also) use chemical sprays that are applied to the field. These chemicals, called pesticides, work in different ways. The farmer selects the appropriate one for the specific pest that is being targeted, and this depends on whether their concern is with a particular weed or insect.

Weeds are usually controlled by pesticides (called herbicides) when the crop (and weeds) are still young. This early spraying results in a more effective application, or better control of the weeds when the crop is most vulnerable to them. However, farmers must be careful about the effects of an herbicide on their crop, as the herbicide can also harm crops depending on the type of plant grown and what weed the farmer is targeting (want to know more?). This has limited the options farmers have for controlling weeds in their fields. In response to these limitations, several genetically modified crops have been developed that can withstand common and effective herbicides. The most common genetic modification is to the herbicide glyphosate. Glyphosate is considered a broad spectrum herbicide (which means it kills a lot of different types of weeds) and is widely used. However, problems have arisen from the wide adoption of genetically modified (GM) crops that are resistant to glyphosate. These crops have bred with weeds and produced glyphosate-resistant weeds. Furthermore, GM crop seeds that grow in subsequent years (the volunteers) are also resistant to the herbicide. Herbicide resistant weeds have become a major problem here in Canada and in many other countries. Farmers must find new ways, both chemical and cultural, to deal with these new superweeds, and options are limited. Read more about the effects of GM crops and pesticide resistance on agriculture.

In modern agriculture, insect pests are generally controlled by pesticides called insecticides. Insecticides can be applied to seeds before they are planted, or can be sprayed onto the crop and insects when suspected or actual damage is occurring. Like herbicides, insecticides have different ways in which they kill insects, depending on the chemical makeup of the product, and are selected based on their efficacy (how well they work) for a particular insect pest. A major class of insecticide used most often across the globe is called neonicotinoids. Because of the high level of use of this insecticide and its persistence (it does not break down easily into less harmful chemicals), it is being found in waterways in high concentrations, high enough to be toxic to beneficial insects. Receiving the most attention in the media is the impact of neonicotinoid use on pollinators, especially bees. Bees can be exposed to the insecticide through sprays, residues from treated seeds, contaminated pollen and nectar, and contaminated water (Neonicotinoid in Ontario). Bees are extremely sensitive to neonicotinoid exposure, but the dramatic reduction in bee populations is not only caused by exposure to the insecticide; there are many other potential contributors, including disease. However, the evidence of a link between population decrease and neonicotinoids is sufficiently clear so that many jurisdictions, including the province of Ontario, are taking action to reduce the use of neonicotinoids in agriculture. Ontario has been working to reduce the area planted with neonicotinoid seed by 80% between 2015 – 2017. Read more about what a reduction in pollinators means for the sustainability of agriculture.




 

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