What do we know about the future of crop pests and pathogens in relation to food systems?

By Athanasios Petsakos, Carlo Montes, Diego Pequeno, Benjamin Schiek, and Kai Sonder

Food, land, and water systems face daunting challenges in the future, and the body of research exploring these challenges is growing rapidly. This note is part of a series developed by the CGIAR Foresight Initiative to summarize what we know today about the future of various aspects of food systems. The goal of these notes is to serve as a quick reference, point to further information, and help guide future research and decisions.

Key messages

• Crop pests and pathogens (P&P) can cause substantial yield losses and pose a threat to global food security. Losses at regional level can even exceed 40% for some crops like maize and rice.
• Most studies show that warmer climate creates a conducive, albeit spatially variable, environment for P&P spread. However, existing foresight research is largely biophysical in nature and focuses on individual pathosystems, examined mostly at national level. As such, projections of the magnitude of economic impacts of changing patterns of P&P are missing.
• Global assessment of model-based historical and future P&P impacts on food systems remains constrained by the small number of available models that can estimate yield losses under contrasting climate and agroecological conditions.
• Further efforts are needed to improve data accessibility, model versatility, and simulation platforms, and to establish international observation and modeling networks.

Recent trends and challenges

P&P present a major threat to global food security, and they have led to several famine events in human history, like the infamous Irish potato famine in the mid-19^th century. Latest estimates suggest that current average losses to P&P for wheat, maize, rice, potato, and soybeans are in the range of 17-30% globally. Losses for maize and rice in the Indo-Gangetic Plains in India even exceed 40% (Savary et al., 2019).

Recent P&P outbreaks and emergencies have put the spotlight on P&P, leading the United Nations to declare 2020 as International Year of Plant Health. Examples of such incidents are abundant: the “Panama” disease, which almost caused a collapse of banana trade in the mid-1900s, is once again threatening banana production worldwide, leading Colombia to declare a national emergency in 2019, and prompting concern about the possible “near-death” of banana cultivation. The recent desert locust outbreak in the Horn of Africa has also triggered international concerns about food security in the region. Similar concerns are even shared by developed countries who have witnessed a potential re-emergence of the wheat stem rust disease after almost 60 years (Lewis et al., 2018).

Climate is one of the most important factors mediating the impact of P&P on food systems. Climate change is thus expected to affect existing pathosystems, leading to epidemiological and distributional changes in existing P&P (Garrett et al., 2006; Bebber et al., 2013). It can also facilitate the establishment of new pathogens, especially when combined with increased trade between countries, as happened recently in the case of the wheat blast disease, which was introduced to Bangladesh in 2016 via international wheat trade. The disease is now threatening wheat production in South Asia, especially those regions where climate conditions are suitable for its development (Montes et al., 2022).

What is the latest foresight research on this topic, and what do those studies show?

Many studies have assessed the potential impacts of climate change on future threats associated with P&P, often examining one pathosystem at a time and at varying spatial scales. Juroszek et al. (2022) reviewed 143 studies performing model-based projections of potential disease infection risks for 30 different crops. The review reveals that more than 60% of them project an increase of infection risks in the future, but results are associated with high uncertainty and exhibit considerable spatial variability.

Chaloner et al. (2021) found that projections (to the late 21^st century) of climate-induced yield changes for 12 crops exhibited positive spatial correlations with infection risks from 80 crop pathogens. These results suggest that, while climate may become more suitable for crop growth over some areas in the future, it will also be conducive to pathogen development. Their analysis further reveals that the number of pathogens developing under suitable climate conditions (pathogen richness) will likely increase in higher latitudes for most crops, except for rice where an increase is projected across all latitudes. For instance, Europe, China, and Peru are expected to face the greatest overall pressure from P&P in the future because of increased pathogen richness and large changes in the composition of pathogen assemblages.

Deutsch et al. (2018) studied the global impact of increasing temperatures on grain losses from insect pests by 2050. Their analysis shows that a warmer climate can lead up to 25% higher yield losses globally per degree of temperature increase. The United States, China, and Europe are likely to face the largest increase in yield losses for wheat (>60%) and maize (>40%), whereas China and South Asia are expected to register up to almost 30% higher losses for rice.

Several authors (e.g., Moretti et al., 2019; Liu & Van der Fels-Klerx, 2021) highlight the increased risks of Aflatoxin contamination with climate change and the expansion of current risk areas (that are mainly in tropical and subtropical zones) to Europe, the United States, and Southern Latitude countries like Argentina and Australia. Increased CO₂, elevated temperatures, drought, and the combination of these factors are expected to increase susceptibility of maize and other crops to the pathogens.

What are key gaps, questions, and opportunities for further foresight research?

 Quantifying the future pressure of P&P on food systems remains a challenge. The difficulty in modeling P&P stems from the complexity of simulating the various processes related to P&P dynamics, which is exacerbated by the existence of multiple pathosystems, the uncertainty related to model parameterization, and the limited availability of data that are needed for model validation and calibration.

Among existing P&P models, only a few have been implemented at regional or global scale, considering long-term climate trends (Juroszek et al., 2022). The number of models that quantify the impact of P&P on yields is equally small, and mostly focused on the main grain crops such as wheat, maize, and rice (e.g., Willocquet et al., 2002; 2008; Batchelor et al., 2020).

The difficulty in quantifying losses to P&P and in accounting for socioeconomic conditions currently presents a major obstacle in linking P&P models with existing integrated foresight modeling frameworks to assess potential P&P pressures to food systems and food security in the future. As such, current foresight work on P&P is largely focused on biophysical processes leading to outbreaks of specific pathosystems, but the link to crop yield responses and to food security is missing. Attempts to combine P&P with economic models to address food security issues are still at embryonic stage, with current research limited to static economic assessments of specific P&P outbreaks (e.g., Godfray et al., 2016).

The need to link epidemiological and crop simulation models to quantify the impacts of P&P on crop development and yield has long been considered one of the priorities for P&P modeling, but also an important challenge (Cunnife et al., 2015; Donatelli, et al., 2017). Recent research on coupling crop modeling with generic P&P modeling (Batchelor et al., 2020; Berton Ferreira et al., 2021), along with the expressed need to create multidisciplinary communities of practice, reveal opportunities for improving existing tools and enhancing our understanding of P&P impacts on food systems.

Authors of this note are Athanasios Petsakos, Scientist, the Alliance of Bioversity International and CIAT; Carlo Montes, Agricultural Climatologist, International Maize and Wheat Improvement Center (CIMMYT); Diego Pequeno, Associate Scientist, Wheat Crop Modeler, CIMMYT; Benjamin Schiek, Senior Research Associate at the Alliance of Bioversity International and CIAT; and Kai Sonder, GIS Laboratory Manager, CIMMYT.

If you have any feedback or questions about this note, please get in touch with Athanasios Petsakos (a.petsakos@cgiar.org).

 For more information, check out these resources:

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Bebber, D. P., Mark AT Ramotowski, M. A. T.and Sarah J Gurr. 2013. “Crop Pests and Pathogens Move Polewards in a Warming World.” Nature Climate Change 3 (11): 985–88.

Chaloner, T. M., Gurr, S. J., & Bebber, D. P. (2021). Plant pathogen infection risk tracks global crop yields under climate change. Nature Climate Change, 11(8), 710–715. https://doi.org/10.1038/s41558-021-01104-8

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Juroszek, P., Bartsch, L., Fontaine, J. F., Racca, P., & Kleinhenz, B. (2022). Summary of the worldwide available crop disease risk simulation studies that were driven by climate change scenarios and published during the past 20 years. Plant Pathology, 71(9), 1815–1838. https://doi.org/10.1111/ppa.13634

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Photo: CIAT cassava specialist Dr. Tin Maung Aye studies cassava crops in northeastern Thailand, which have been affected by a combination of pest and disease outbreaks. Credit: ©2009CIAT/NeilPalmer