Fungi are ubiquitous and vital members of nearly all ecosystems on our planet, from untouched wilderness to carefully managed agriculture. In our interaction with these creatures we have experienced both extraordinary benefits—including harnessing the process of fermentation—and terrible losses—including the Irish Potato Famine. The majority of fungal species are detritivores, quietly decomposing and recycling organic matter in soil or water. But some species are parasites, and they can threaten the health of humans, our crops and livestock, and wild species. There are a variety of methods available for managing fungal pathogens, and each presents a mixture of costs and benefits. Chemical fungicides are the most consequential of these management options. One of the potential costs of these chemicals is the risk of the fungal target evolving resistance to the fungicide, until it is no longer an effective treatment.
In this document, we present the essential background information necessary to understand the risk of fungicide resistance, and provide two case studies of fungicide use and resistance. These examples provide a portrait of modern agriculture in which widespread and indiscriminate fungicide applications have led to an increasing risk of fungicide resistance; reducing our ability to protect ourselves and our crops from the substantial, and sometimes catastrophic, effects of pathogenic fungi. To go along with this increased risk of resistance, recent trends in global trade and climate change have increased the incidence of dangerous emerging fungal diseases.
Our first case study takes us to The Netherlands, where a ubiquitous soil fungus, Aspergillus fumigatus, which can infect immunocompromised humans, began to show resistance to the azole family of medical fungicides. These chemicals are widely used in agriculture and medicine, and numerous lines of evidence indicate that this fungus evolved resistance to agricultural products before infecting humans. The consequences of this resistant fungi are sobering: 12 weeks after receiving a diagnosis, a staggering 88 percent of patients with a resistant infection had died. Although this environmental origin of this resistance has not been proven, it is now the leading hypothesis, and strikingly illustrates the serious consequences of resistant fungal pathogens.
The second case study is set on the vast corn belt of the American Midwest, where fungicides were rarely used before 2007. However, recent volatility in corn price have driven farmers to abandon non-chemical control options in pursuit of higher yields, leaving fungicides as the only recourse in the face of disease. Strobilurins, a common family of fungicides began to be marketed in corn to promote general plant health, even in the absence of disease, and the use of fungicides in corn was hugely expanded. However, a number of careful studies showed that these chemical applications generally fail to provide any financial dividends, and strobilurins have proven to high risk for the development of resistance. The widespread use of fungicides under these conditions shows vividly the considerable risk for the development of resistance that is created within the modern agricultural system.
These case studies are simply two examples of a much larger trend: the over-reliance on simple chemical solutions to complex ecological and evolutionary challenges. We need to abandon this myopic approach to agriculture because unnecessary fungicide applications increase the risk of resistance, the consequences of which may be quite dire indeed.