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Monday 14 May 2018
14 - 17
Stanhope Hotel,
Rue du Commerce 9,
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Non-ETS targets

Climate change


Reduction of pesticides in agriculture is necessary to stop the decline in biodiversity and to ensure a more resource efficient approach.

By Hans Nielsen, The Ecological Council Denmark

Reduction of pesticides in agriculture is necessary to stop the decline in biodiversity and to ensure a more resource efficient approach.

This reduction can be achieved by a combination of the introduction of

  • advanced technology in conventional agriculture
  • spraying-free zones, for instance along rivers and steams
  • more organic farms.

In this article we will concentrate on the introduction of advanced technology.

Danish studies have shown that the number of wild plant species from 1970 to 1990 has been reduced by 60% in the cultivated fields (Andreasen, C. et al. (1996)). Moreover, the pesticides also damage the natural flora and fauna on the boardering conservation areas, furthermore, they may cause contamination of groundwater.

Weed that can grow in cultivated fields comprise approx. 200 wild plant species, but approx. 80% of them are so weak in the competition with the crops that they do not affect yield substantially in any well-run farms. It is therefore mainly the remaining 20% of weed species that are so competitive that they can affect the yield significantly. The 20% of damaging weed is the reason why the combat against pests continues to increase.

Figure 1: Treatment frequency for pesticides 2000-2010 (Three year average).

Source: Environmental Protection Agency's pesticide statistics.

It is time for a paradigm change to make sure that farmers leave the approach of killing pests and in stead start managing pests. This means that the farmers in the future must target the 20% of weed species which cause significant yield losses, while leaving the remaining 80% of weed species, which does little harm or in some cases can even help to increase crop yield.

It is time to abolish the idea of killing all pests, to obtain a paradigm change where we start to manage pests, applying a combined approach of mechanical, chemical, thermal, or biological combat of pests to allow that weed again will start to grow in arable land.

The start of the pest management approach

At the heart of this new approach, each farmer will need as from 2014 to deliver a sustainable package of mandatory agronomic practices.

Agricultural practices that can minimize the risk of significant yield losses due to weeds include:

  • a wide crop rotation, to prevent the weed from spreading  dramatically
  • choice of crop varieties that grow quickly in spring and minimizes the amount of light that reaches down to the weeds
  • placement of fertilizer in the soil under the planted crop, so fertilizer is not available to the weed, which sprouts from the surface
  • split fertilization, so the fertilizer allocated for several laps as the crop, so there is a small amount of fertilizer available to weeds

Agronomic practices that can minimize the risk of significant yield losses due to attacks of insects and fungi include :

  • A wide crop rotation, which prevents that pests can propagate themselves so much that they result in significant yield loss, such as nematodes in sugar beet (1 in 3 years rotation needed), fungi attach in  crucifers (1 in 5 years rotation needed).
  • choice of crop varieties that are fully or partially resistant to pests
  • fertilization in a way so that the content of nutrients in crop plant juice is reduced.
  • reduced crop density, so the risk of fungal attack is reduced because of lower humidity.

Fighting pests with insecticides significantly impoverish both insect life, birds and wildlife that feed on insects. The vast majority of insecticides are used in cereal production, where the yield loss caused by avoiding spraying generally is only a few percent. As a result consumption of insecticides can be reduced drastically without leading to significant yield loss. Reduced weed control will help to ensure more hiding places and habitats for wildlife that eat the pests. Establishment of buffer strips, especially for cereals, is a tool to ensure establishment of conventional biological control.

On top of this, and as a voluntary requirement to be financed as part of Rural Development Programme, the farmer could take advantage of new technologies understood as precision farming such as :

  • Use of injection syringes: can help the farmer to reduce pesticide use. Typically pesticide and water will be mixed as a fixed mixture for the whole capacity of the sprayer, which can be up to 100 hectares. In contrast injection syringes allow the farmer to select different mixtures of pesticides in a single field and for different fields. Also, as injection syringes uses clean water to mix during spraying, the operator can continuously change which concentration of the single pesticide to use. It also means that there is no residue of diluted pesticides in the sprayer after spraying, and as a result no pesticides mixture being dumped afterwards.

  • Use of GPS : can reduce pesticide consumption by approx. 10% as it for instance prevents double treatments in wedges and while turning.  GPS can also be used to calculate the needed amount of pesticides to use. Finally, GPS can be connected to sowing machines or a planting machines allowing the seeds or the plants to be placed in a pattern, which afterwards allow to hoe the plants across the rows and to hoe closer to the rows than what is possible without GPS.
  • Weed-eye technology : the Danish Railways (DSB) uses recognition technology when spraying along the railway tracks to prevent destabilization due to plant growth, by use of blue, red and infrared light. In these cases spraying is targeted at the elimination  of the actual vegetation. This technology can be developed into a recognition technology, where the different weed species can be distinguished. Recognition technology is placed in front of the sprayer filming the weed species, and a computer determines which pesticide to use and the dosage. Registration can also be used to obtain information on whether there is emerging weed problems, which need to be prevented by changing rotation. In the longer term, this technology could be improved to allow for a selective control of the injurious weeds.

So there is a lot of techniques to explore to make it possible for farmers to take a more      resource efficient approach to pesticide use and in this way contributing to stop the decline in biodiversity.



Focus on pesticides. The Ecological Council, the 2,001th

Andreasen, C. et al (1996): Decline of the flora in the Danish Arable field. J. Appl.            Ecole., 33, p. 619-626.