A diverse approach to manage agricultural pests and diseases

The diverse varieties of individual crops represent a precious resource that poor farmers can use to manage pests and diseases, according to Devra Jarvis, the Bioversity scientist who is global coordinator of a project to research the ways in which farmers make use of diversity. She was speaking at the wrap-up symposium of a three-year project that brought together farmers and scientists in four countries – China, Ecuador, Morocco and Uganda – to study how diversity of varieties in six crops: banana, barley, common beans, fava beans, maize and rice could be used to reduce pest and disease damage.

The overall conclusion, for most crops at most sites, is that the average damage due to pests and diseases was lower for farmers who grew three or four varieties. There was also less variability in the amount of damage. Some farmers who grew just one variety might be lucky and not suffer much disease; others lost almost their whole harvest. Farmers who grew more varieties had less disease overall and even the worst of them did relatively well.

Studies in Morocco focused on barley and faba beans, which together are the most important crops that are often the core of farm activities. Farmers grow more modern varieties to sell, because they get a better price, and they report higher disease damage on the modern varieties. Traditional varieties have less damage, especially when more than one variety is grown on the farm. In China, maize and rice farmers who grew more varieties also had less disease. Researchers from Ecuador reported similar results for bananas, common beans and maize. In Uganda too, more diversity had the effect of protecting bananas and common beans against diseases.

Researchers also reported variability in the susceptibility of varieties to the target pests and diseases and in the virulence of different diseases on the host varieties. This represents an additional layer of complexity that the farmers themselves are sometimes not aware of. Project scientists expect that by uncovering this kind of information, and then working with farmers to ensure that they understand and can make use of it, the effectiveness of diversity against pests and diseases can be further enhanced.

An important element in the project planning was its global reach and chosen crops, selected to enable comparisons to be made and lessons learned.

“Crops were decided upon jointly by the four countries so that they not only covered a variety of breeding types but also because they were important crops for food security, with high traditional varietal diversity in more than one of the partner countries,” Devra Jarvis said. “Working as an international team, we  are able to understand more about what works under different conditions and to see what we can learn from farmers across countries and cultures to enable us to adapt and share best practices.”

It was noted, for example, that while farmers in one country had a good understanding of the pests and diseases that threatened their bananas, those in another country didn't. Nevertheless, both groups benefited to some extent from the protection afforded by biodiversity. As farmers learn more one would expect them to benefit more.

The use of crop diversity to combat pests and diseases can be thought of as an element of integrated pest management. IPM has so far mostly been about changing the living and non-living environment in which modern crop varieties grow to make those varieties less susceptible to pests and diseases. The hope is that the use of diverse varieties against pests and diseases will become an integral part of IPM.

The meeting will end with a session devoted to policy and the formulation of advice that governments and others can use.

Devra Jarvis expressed the hope that “as a result of this project and the meeting countries will recognize that using crop diversity is an inexpensive, sustainable option to allow farmers to protect their harvests from pests and diseases. Furthermore, this approach is future-proof, and will enable farmers to adapt to changes in pests and diseases brought about by climate change.”

For more information, contact:
 Devra Jarvis

Note: The three-year project was funded by the Global Environment Facility of the United Nations Environment Programme (UNEP/GEF), the Swiss Agency for Development and Cooperation (SDC), the United Nations Food and Agriculture Organization (FAO), and Ford Foundation.