Pesticides and agriculture: The cohesion of a system

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Temps de lecture : 4 minutes  

Upon the request of the Agriculture and Environment ministries, a collective scientific assessment led by the INRA (National institute for Agronomic Research) and CEMAGREF (Institute for Agricultural and Environmental Research Engineering) produced a knowledge review upon which actions to reduce the current level of pesticides and their environmental impacts could be based. Excerpts.

Some crop systems generate high phytosanitary risks

Pesticides are used because of the risk of the development of attacking bio-agents (self-propagating agents, fungicidal diseases, devastating insects etc.). These risks are even greater when the aggressive bio-agent encounters, over large areas and time, favorable conditions for its development. Now intensive and specialized crop systems intensify the risks: monocrop or successive crops with same vegetation cycle do not allow the development cycle of aggressive bio-agents to be broken and dense vegetation contributes to the proliferation of diseases, while strong fertilization also benefit self-propagating agents and disuse of ploughing means self-propagating agents’ seeds or pathogenic agents are no longer deeply buried.

In these conditions which maximize the sanitary risks, pesticides seem to be the necessary and efficient solution.

But the repeated use, over large areas, of the same active substance, quickly leads to the development of pesticide-resistant populations of the targeted aggressive bio-agent. Currently, in France, all agricultural production (intensive farming, fruit arboriculture, vineyard), is confronted with resistance problems, and concern most chemical categories of pesticides.

The reliance of agricultural production on pesticides

The technical logic behind intensive crop systems is strengthened by relatively inexpensive pesticides compared with the cost of other production factors and agricultural production themselves. On the other hand, less pesticide-reliant techniques are more complex to set up, generate considerable direct and indirect costs, especially when acquiring the information necessary to their implementation (training, field observation time, analysis and consulting fees etc.)

They are also thought to be more “risky”, in the sense that gross outputs and profits seem to be more variable, although this is not always verified (see the corn case below).

The technical and economic reliance of agriculture on pesticides depends on the crop type. It is heightened by distribution requirements and those of the consumers for zero-default products that can be preserved for a long time. The fact that consulting on phytosanitary protection, input sales and harvesting is increasingly offered by the same organizations does not favour the development of alternatives to reduce dependence either.

“Reasoned” use of pesticides: The expected results are not to be overestimated. […]

”Reasoned” use of pesticides may lead to eliminating systematic pesticide use

But, it is above all, the reasoning behind product choice, dosage and application conditions which is likely to significantly reduce the quantities used. However, this approach seems to be limited as long as we keep on using crop systems that create substantial phytosanitary risks.

Furthermore, this practice comes at a high cost: it includes diligent monitoring of land plots requiring much qualified work, risk of substantial crop losses in case of a diagnostic error, risks for forthcoming crops if non-treatment allows the survival of residual aggressive bio-agents etc.

“Reasoned” pesticide use does not constitute a temporary phase of a pesticide reduction strategy insofar as the pressure maintained by bio-agents can threaten its sustainability.

“Alternatives” to fighting chemicals: No ready-use solutions

Farmers often request “alternative techniques” to pesticide use, that are as easy to use, efficient and cheap as phytosanitary treatments, technically more sustainable and do not affect their high output objectives. However, there is no such technique that meets all these requirements.

Some “complete” genetic resistance varieties to aggressive bio-agents – the “ideal” substitute – have turned out to be just as swiftly bypassed by the targeted aggressive bio-agents as pesticides are; it is the same for chemical or biological “total” fighting techniques. Physical processes, such as mechanical or thermal weeding, are not subject to this risk, but are often far more time and energy consuming than spraying, or cannot be used on large areas (protection nets).

Other techniques, such as partially resistant varieties, biological deterrents, work on the soil, only have limited efficacy. They control aggressive bio-agents, under the condition that they are used together, and are used with certain crop systems and crop stage management systems that reduce the risk of aggressive bio-agent development. The range of methods available is wide, and the optimum combination needs to be determined according to type of production concerned.

Integrated production: A necessary approach

Therefore, the idea of an “alternative technique” does not seem very relevant; instead, we should prefer “an alternative strategy” for crop protection. This would be based on the implementation, case by case, of a few principles of action where prevention against phytosanitary risks comes first.

This is the aim of “integrated production”, which re incorporates the management of the aggressive bio-agents in the design of crop systems, or even production, based on scientific data and renewed techniques. […]

The integrated approach may be illustrated by “rustic” corn varieties grown in accordance with “low input sales” technical paths. A limited decrease of the yield objective enables crop behavior which reduces phytosanitary risks and consumption of pesticides. The economic performance is on average comparable to that achieved in more intensive systems (and superior when the price of corn decreases); the variance is not increased.

As organic farming abandoned synthesis pesticides, it is a strong contender as “an alternative strategy”, but other systems could also be designed which tend towards “zero pesticides” without prohibiting the use of synthesis fertilizers or occasional use of phytosanitary treatment if prophylactic and non-chemical curative measures failed.

Managing phytosanitary issues needs to be re contemplated in terms of a” healthy crop system” than in terms of the “fight against crops’ enemies”.

Collective scientific assessment led by INRA/CEMAGREF.

“Pesticides, agriculture and the environment: Reduce the use of pesticides and limit their environmental impacts” – Restitution symposium – 15th December, 2005

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