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12 February 2021

ORFC Global in review: when the medicine feeds the problem

When the Medicine Feeds the Problem: How Nitrogen Fertilisers and Pesticides Enhance the Nutritional Quality of Crops for their Pests and Pathogens

Speakers: Ulrich Loening, Daisy Martinez
Broadcast at ORFC Global, Saturday 9 January
Watch again on YouTube

Session review by: Charlotte Chivers

I attended a fascinating talk at ORFC Global in January. Researchers from the University of Edinburgh shared their findings in relation to how pesticides may, paradoxically, benefit crop pests.

The research was born from the work of French agronomist, Francis Chaboussou, who observed that agrochemicals were leading to more pressure from pests. He wondered why this was, and dedicated his life to finding out, both through experiments and reviewing the literature.

How pesticides can end up feeding ‘pests’

The central idea developed by Chaboussou is that most pests depend on the availability of amino acids, the building blocks for proteins which are vital for plant growth and repair.

Plants make proteins out of amino acids through a complex process. Before amino acids have been used up in this process, they provide a good source of food for pests and parasites.

Amino acid concentrations in plant cells are usually kept at low levels, because they are quickly used up by the plant when making proteins. But the application of pesticides can temporarily prevent the plant from producing proteins. Result? Proteins are converted back into amino acids – in other words, back into food for a variety of organisms.

This means that pesticide applications can increase the amount of food available, and feed the very problem they attempt to solve. A spray may kill greenfly, but then inadvertently provide food for fungi, resulting in fungal infection. The result is a treadmill of pesticide applications.

You can read Chaboussous’ book for free here.

Other effects of pesticides on crops

Daisy Martinez and colleagues from the University of Edinburgh recently completed a literature review exploring Chaboussou’s conclusions. It confirmed many of his findings.

The review also indicated that crops may become biochemically stressed by pesticide applications. This stress may not be obvious; changes are subtle and occur within the plant’s cells. The outcome of this shift is an accumulation of amino acids in crop tissues. Again, this increases the amount of food available for pests and pathogens. Similar results have been found in response to nitrogen fertiliser applications.

More research is needed to explore the effects of using fertilisers and pesticides together, but the work done so far certainly underlines the paradoxical effects of pesticides, and the vital need to look at the complex nature of ecological interactions in farming.

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