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Crop protection: Alternatives to agrochemicals

By Thomas Preuße, DLG Mitteilungen

Basic agricultural college learning teaches us that integrated crop protection combines field and crop cultivation measures with mechanical-physical, biological and chemical procedures, the latter according to the motto: »As much as necessary, as little as possible«.

Intensification in arable farming over the last decades has led to many chemical crop protection measures sometimes emerging as indispensable, followed by the all-too familiar production penalties  through active ingredients ceasing to be used in the field (e.g. through official banning) or losing their efficacy (through resistance development). This leads to increased interest in crop rotation, resistant varieties or mechanical weed control. Hopeful alternatives in this respect are also biological and biotechnical procedures, as well as for digitalisation in general.

The removal of active ingredients is no surprise

The increased requirements to be met for marketing and application approval, industry concentration on the most promising crops and growing regions (to which Europe does not automatically belong), as well as the »victory progress«  of herbicide tolerant crops: all factors have played, and continue to play, a role in reducing the number of officially approved products available. Insecticides achieve official approval only with difficulty with the result that susceptible gaps in protective cover now exist, for instance in Germany with oilseed rape, sugar beet and potatoes. For years now, further development of herbicides has been effectively blocked by the presence of glyphosate. Only now, the initially unexpected appearance of resistances has companies refocussing on this segment, although most action just now is centred around finding new fungicidal ingredients.

Three different active ingredients necessary

It’s been more than ten years since the EU decided to move away from risk assessment in official substance approval procedure and more towards critical substance properties: keyword »cut off«. The effect of this principle is now increasingly noticeable with well-known active ingredients falling victim one after the other and no longer receiving EU approval. The industry calculates that in the medium term only 100 to 120 substances will remain. In 2019, there were still 440 on the EU list. Taking Germany as just one example, the pressure is additionally increased by the country’s Federal Environment Agency having a veto right in the official approval process – and continuing to use this to make achieving national authorisation as difficult as possible. What’s really needed to avoid  build-up of resistances is the availability of at least three different active ingredient mechanisms. Particularly with »small area crops« this target has no longer been achieved for some considerable time.

Crop protection substances: Repeated reformulation and new combinations

Development costs and time of over 300 million € and ten years encourage firms to increasingly look to »repackaging« of already known substances, involving new combinations and new formulations. The innovation perspective with chemical (but also biological) crop protection tends nowadays nearly always to lie in the formulation rather than in new active ingredients! Where new ingredients are unavailable, at least the efficacy of the old ones might be improved and thus the amounts applied reduced, or the environmental effect bettered. The formulation route is not only the best way forward for the generic product manufacturers with their patent-free active ingredients in order to unlock new properties from older ingredients, or at the very least to get onto the market with a »new« product. If one does in fact find a new formulation technology, then this can be used with a number of substances. After all, there’s no need reinvent everything. Just look at the pharmaceutical or cosmetic sectors. What matters there too, are active substances and excipients.

Biologicals: Reasonable expectations required

Biologicals in the form of biological crop protection substances and biostimulants are seen as promising products. The  requirements for practical application were at times chaotic, although now legally regulated.

  • Biological crop protection substances are subject to all requirements under the Crop Protection Act. The respective official authorisation is therefore just as demanding as that for chemical crop protection substances.
  • Biostimulants often work within the border area between crop protection and plant nutrition and come under the Fertilising Products Regulation that came into effect in 2019, though no shortage of arguments and open questions still remain.

Those who can, try to bring their products under the biostimulants heading because such products require no expensive testing but simply a description and a »proof of efficacy«. Here, the Fertilising Products Regulation has an important task: to make more transparent the many products sprouting up in the area of biologicals. Especially worrying:  the kind of products that promise much and deliver little. Just how complicated this can be in detail is evident by taking the example of potassium phosphonate. While this has a pure biostimulant effect, it can also control peronospora fungus (in organic wine production) and so must be registered under crop protection substances although explicitly not under the  Fertilising Products Regulation.

Sobering trial results with biologicals

In Germany, the crop protection services of the various federal states have run a series of plot and field trials over some years. The results consistently do little to encourage euphoria, at any rate in the medium term. It would therefore be wrong to assume that these products are ready to replace chemical crop protection substances. The results are too unreliable and too dependent on environmental conditions. The same applies to combined biological and chemical procedures with the chemicals involved bearing the main burden of efficacy. But with the increase in results and related experience, such efforts should certainly not be filed away and forgotten. For biologicals too (above all regarding formulation and therefore stability), intensive further development will continue.  However, their degree of efficacy in arable cropping will tend to remain at 40% for some time rather than 90%. Perhaps the future lies in a combination of »chemistry« and »biology«. Basic requirement continues to be a broad spectrum of very effective crop protection substances.

A future for RNAi and nanopesticides?

Two further subjects, RNA interference (RNAi) and nanopesticides, still mainly lie well in the future.

This year though, an RNAi solution against corn rootworm has already won official authorisation for use in the USA.  Its principle is that – genetically modified!  - maize produces RNA snippets that can block the action of a growth determining gene in the rootworm. RNAi emerged from genetic research where the effect of single genes can be identified through deliberately »switching them off«.  In Brazil, a permanent RNAi defence against viruses has been genetically installed in beans. The principle also functions without genetic engineering, although with markedly reduced success. Hereby RNAi snippets are applied in the field just like a crop protection spray and taken up by the crop plants where they block the targeted gene of a pest.

Nano stands for »very small« and the term’s use here underlines that substance components under 100 nanometres can, through this characteristic, have useful attributes. Copper, for instance, has nanoparticles of this size. As can be easily imagined, active ingredients with very small particle sizes might be able to offer better solubility in water.  However, there is still no proof of this in field work.


Alternatives are being sought everywhere. Large investments are being made in biologicals although we must accept that, at least for the foreseeable future, the considerable performance expected of them in conventional arable systems will never be achievable without the support of »chemistry«. What’s still needed is a large enough number of effective substances - unless the aim is for widespread ecologicalisation or greening, although the present free market prices would never allow such a development.