Does science matter anymore? That’s what many asked after an article last month in The New York Times suggested that a deadly fungal outbreak in humans may have developed from a resistance to agricultural fungicides.
In response, one of the nation’s largest winemakers, Constellation Brands, sent a blanket order to its vineyards to pull eight well-established fungicides. The Fortune 500 company, with brands like Robert Mondavi, Clos du Bois, and Fransciscan Estates, made the decision despite any scientific evidence connecting the outbreak to agriculture. No regulatory agencies have acknowledged a link.
Pest control advisors (PCAs) now fear this type of action will have a chilling effect for winegrape growers in their management decisions and lead to an increase in fungicide resistance, while also seeding an outbreak of lawsuits, similar to the wave of cases related to glyphosate.
The Times article details the dramatic race to combat the drug-resistant fungal disease, known as Candida auris, which has popped up in hospital rooms in several countries over the last five years. It is a disease the medical community takes seriously. It kills vulnerable patients within 90 days and has a 50 percent success rate.
According to John Aguirre, president of the California Association of Winegrape growers, the agricultural community would also take this threat seriously.
“We absolutely will be the first to participate in protecting public health,” he said, “if there is a public health issue here.”
Causation vs. correlation
While the Times article notes the mystery over the source of the fungal resistance “remains unsolved,” it does advance a theory from epidemiologists that an over-reliance on agricultural fungicides has created environments favoring the resistant mutations.
The reporters refer to widespread antibiotic resistance found in livestock and cite a 2013 paper in Plos Pathogens that found a separate drug-resistant fungus, Aspergillus fumigatus, in soil samples across the Netherlands. While those soil samples were mostly taken from flower beds in and around infected hospitals, another study did find resistant A. fumigatus in compost from a nearby nursery and a garden center and associated that with widely-used azole fungicides in “grain-growing and grass-growing environments.” The Plos paper does recognize that “conclusive evidence linking agricultural triazole fungicides to the emergence” of resistant strains “in controlled field experiments is lacking.”
While the origin remains unproven, the leading hypothesis still points to resistance found in the natural environment prior to outbreaks in humans.
For both fungal varieties, human cases of resistance were discovered mostly in wetter European environments, where crops are more vulnerable to fungal diseases than Mediterranean climates like California. Two cases of resistant C. auris, however, have been found in patients in California, out of a population of over 39 million people.
“It appears that there is a lot more work that needs to be done to determine what's giving rise to drug resistant Candida auris,” said John Aguirre. “There's a very real difference between research that occurs in the lab versus what occurs outdoors.”
Resistance rises with fewer pesticides
Winegrape growers and pest control advisors (PCAs) are quick to point out that FRAC rotations already tackle this issue and have been doing so for almost 30 years.
CropLife International created the Fungicide Resistance Action Committee (FRAC) to provide management guidelines to growers. FRAC organizes technical working groups to determine best practices to reduce the risk of developing resistance. This extends the effectiveness of fungicides and limits crop losses if resistance does happen. The aim is to rotate the fungicides according to the specific cellular processes they inhibit, or mode of action (MOA), along with the available integrated pest management (IPM) strategies.
The USDA also set maximum residue levels for fungicides, not as much for combating resistance as for reducing levels for all pesticides that may be detected on foods. The California Department of Pesticide Regulation (DPR) also tracks all fungicide use through mandatory pesticide use reports.
Farmers have their own incentives for avoiding resistance as well.
“The foundation for this is good cultural practices,” said Aguirre. “You manage irrigation, fertilization. You prune. You shoot, thin and pull leaves—with this idea of having good fine balance, and allowing light and air circulation throughout the fine canopy.”
Aguirre said this gets “hammered in the head of growers all the time,” along with rotating chemical products. California winegrape growers are well aware of the threat of resistant pathogens. They are careful in managing powdery mildew, a fungal disease that can destroy grape quality and yield, along with the bacteria that causes Pierce’s disease, which has threatened the state’s entire industry. Economic pressures drive their decisions. Without the canopy management, Aguirre said, spraying would be less effective and “it’s just money down the drain.”
With the specific azole fungicide products Constellation listed (Elite, Viticure, Rally, Mettle, Luna Experience, Laguna, Inspire Super, Quandris Top), the economic impact on growers would be minimal, according to Paul Crout, a pest control advisor working in wine grapes. Alternatives are available without significantly higher costs.
Taking products from growers, however, leaves them fewer tools to rotate through in their resistance management and IPM programs and leaves them vulnerable to fungicide problems.
“The whole idea behind resistance management is to have as many different modes of action as possible,” he said, adding that resistance happens when using one MOA repeatedly, as with anti-biotic resistance in medicine.
The glyphosate effect
“We've seen this kind of knee-jerk response to headlines about active ingredients with materials like glyphosate,” said Crout. “Companies are prohibiting the use of these materials without any sound scientific reasoning.”
Crout was referring to the recent Monsanto court cases against the glyphosate product Roundup, which courts ruled against the company despite the EPA determining the herbicide is not carcinogenic.
Andy Wilson, a PCA for Grow West, said that growers and PCAs want to be a part of the solution but depend on research to back up their recommendations. “We want to base decisions of use or not use on sound science,” he said. “But we need proper information on the products that we use in order to make those decisions.”
When asked for comment, a spokesperson for Constellation Brands responded that it is common practice "to send communications to our vineyard teams to provide updates on approved and/or banned vineyard management methods and materials."