In the early summer of 1968, farmers in Louisiana noticed small, elongated brown lesions running down green leaves of corn. These plants quickly died or experienced extensive rot that rendered the vegetable inedible. By 1970, these symptoms could be seen on acre after acre of corn from Florida to North Dakota. The disease soon had a name: southern corn leaf blight (SCLB). The fungal pathogen that caused SCLB, although virulent, could only infect a specific hybrid of corn. This hybrid, which was bred to develop a more efficient ear, was one of the most planted seeds in the country at the time. Once the cause of the vulnerability was discovered, seed companies simply switched hybrids. By 1972, the American corn market rebounded—although not before suffering major economic losses.

The world is now more cognizant of catastrophic biological risk. However, the focus is mainly on direct impacts to human health. The 1970 SCLB epidemic (technically termed epiphytotic) is a prime example of a fast moving plant disease that can inflict sudden and outsized damage to the agricultural industry. Is there significant biorisk to America’s food production and supply? In light of increasing food demand for a growing population and the easy conveyance of biological threats via global trade/travel, let’s explore potential biosecurity vulnerabilities in America’s agricultural industry and discuss possible solutions to mitigate these vulnerabilities.

Why fret about American food security? In its entirety, the US agricultural industry produces approximately $136 billion worth of food yearly and total agricultural services of $1.1 trillion. Net-food importing countries as well as developing nations depend on American agriculture. Thanks to this plethora of food, America enjoys the largest export shares of corn, wheat, and soybean markets. By a wide margin, the country donates the most food to aid programs worldwide—2 million metric tonnes of food in 2012 (the last year that the World Food Programme reported this statistic). Consequently, America is considered an essential breadbasket that must be secure. 

The cost of disease

In any particular year, flooding, severe storms, drought, weeds, disease, and a confluence of other factors can cause reductions in crop yields. It can be difficult to separate losses exclusively due to disease and pest infestation on a national level. Researchers estimate that 20-40% of total crop loss is due to pathogens, pests and weeds. The outcomes of pathogen infestation can be economically, politically, and socially consequential. These impacts are typically calculated by measuring losses from reduced food yields as well as decreased customer demand or exports due to trade restrictions levied by other countries.

For example, annual wheat losses due to wheat rusts, a prominent fungal infection, are estimated at $5 billion globally, with losses due to Fusarium head blight estimated at $3 billion annually. Soybean rust, another fungal infection, causes several billion dollars in soybean damage a year in Brazil and was once projected to do as much in America in the near future. (This did not, in fact, come about.) Citrus greening has significantly decreased citrus yields in Florida and Xylella fastidiosa has hurt vineyards in California and Europe. The highly valued and dominant American chestnut tree became functionally extinct due to chestnut blight.

Livestock and poultry encounter similar if not even greater patterns of losses. African Swine Fever (ASF) cost China north of $100 billion in direct/indirect losses, and if it were to spread to America, the disease could cause an estimated $15-50 billion in damages. In 2014-2015, 12% of egg-laying chickens in America died of avian influenza or were culled to curb the disease, resulting in major losses. On average, economic impacts of a major agricultural epidemic range from $2.5-4 billion. Here are two recent Metaculus questions on livestock culling that are worth considering:

Transmission vulnerabilities 

For any epidemic to truly take root, the following is generally required: The environment must be hospitable, the hosts must be susceptible, and the pathogen must be virulent. 

The sheer number of concerning agricultural pathogens is daunting. To give a sense of scale, this study, which solely focused on staple crops, analyzed 137. Such pathogens are relatively easy to introduce, transport, and transmit. Stopping the introduction of these pathogens, accidental or otherwise, is a seemingly insurmountable task. 

Plant pathogens have highly evolved methods of dispersal that hamper eradication. Pathogen spores can travel many miles via wind; soybean rust is theorized to have made its way to America from Columbia on the winds of several hurricanes. Ug99 wheat stem rust, a feared fungus that 80-90% of wheat plants are susceptible to, has traveled thousands of miles from Africa to Europe via wind. The monoculture that extends across the Corn Belt and beyond provides a robust corridor for pathogens such as Ug99 to move efficiently across the country. Crops can also contract disease simply through contact with infected farming equipment or leaf splash during a storm. Citrus canker previously damaged the Florida citrus industry via these dispersal mechanisms. 

American farms are constantly exposed to new pathogens and pests through international trade/travel. Some pests are especially hearty. For example, the khapra beetle, which feeds on wheat stores, can survive without water for years at a time, allowing it to travel long distances in search of food stores. Its diminutive stature makes it incredibly difficult to detect. The USDA has intercepted hundreds of cases of khapra infestations at border inspections over the past decade. Unfortunately, according to agroterrorism expert Henry Parker, “more than nine million imported food shipments cross the borders of the United States annually at 360 border entry points, but only about one percent is inspected.” In such cases, unfavorable environmental conditions are the only barriers to the development of large-scale epiphytotics. 

The country's best defense against plant pathogen transmission is its climate. Plant pathogens typically require warm, wet weather to reproduce at high levels. Although a disease may wreak havoc in a given year, Northern America winter temperatures have historically provided an opportunity to kill remaining pathogen inoculum, thereby limiting losses. Disease and pest infestations are particularly finicky because environmental conditions such as extended drought can curb even the most potent fungal infections. Unfortunately, this natural defense system may be compromised by the burgeoning effects of climate change. Rising temperatures and shifting precipitation patterns indicate hotter, wetter conditions in the Midwest, with a severe decrease in unfrozen days in winter. Do you think temperatures will continue to rise in the 21st century? If so, pathogens that have historically failed to establish populations in the country, especially tropical pathogens, may be more likely to thrive.

Supply chain vulnerabilities

The success of modern agriculture can be attributed to our ability to manipulate the environment via increases in fertilizer and herbicide/pesticide use, efficient irrigation, enhanced storage, improved farming equipment, information sharing and more. Uniformity is also a key driver of agricultural success, with large farms dominating food production output. However, a monoculture is vulnerable to disease because its genotype is identical across all individual organisms. SCLB exploited a genetic vulnerability found in the hybrid corn used in 1970. Currently, the fungal diseases black sigatoka and fusarium oxysporum TR4 have infected a majority of the world’s banana trees, which lack resistance, potentially endangering the global banana stock. In 2016, a researcher who sequenced the TR4 commented that the industry could be wiped out in 5-10 years. This prediction did not come to pass, but might it in the future?

Just-in-time supply chains dictate that farmers no longer produce their own seed nor have the equipment to clean it. Instead they almost exclusively buy seed from agriculture tech companies. These companies, through economies of scale, provide seed that boasts germination rates of 95% and anti-fungal coatings that provide adequate protection against many serious pathogens. Unfortunately, this consolidation of business has incrementally bred out the individual farmer’s ability to self-sustain. A security breach at a major agricultural technology company or the development of another exploitable genetic vulnerability could result in considerable losses if seed were recalled or susceptible to novel pathogens.

Agroterrorism

In 2004, former Secretary Tommy Thompson of Health and Human Services famously said: “For the life of me I cannot understand why the terrorists haven’t attacked our food supply because it is so easy to do so.” Since 9/11, this has been a common refrain for national security experts. Logically, agroterrorism makes sense. Agricultural facilities are soft targets that have little security infrastructure. Moreover, Americans have come to expect a safe, cheap and plentiful food supply. Any disruption to this reality could create substantial social unrest and wreak havoc on consumer confidence. It’s rumored that military intelligence found several Al Qaeda-authored lists of pathogens that could target plants and animals. The US government developed and used herbicide in combat, and North Korea may still be developing dangerous bioagents to this day.  Nevertheless, there are barely any instances of terrorist attacks on farms, feedlots, or ranches. Will this continue to be the case moving forward?

Solutions 

Food security may be at risk, but there are actionable ways to protect against damage from pathogen infestations. Here are a few solutions that are already in-process or that should be:

1) Develop technology and systems that detect infestations early. USDA’s IPM Centers and National Animal Health Monitoring System help farmers and ranchers share on-the-ground pathogen incidence data, but this only scratches the surface of what’s needed. USDA, DOD, DHS, FDA, and the FBI all have adept yet siloed food defense capabilities. In February 2020, the GAO recommended alignment and coordination across agencies to better address pathogenic threats. Funding for specialized research facilities such as the National Bio and Agro-Defense Facility in Manhattan, Kansas is imperative too. And certainly, innovative technologies such as assays, nanotech and remote sensing could play a substantial role in detecting disease early. Vertical farming could prevent infestations altogether.

2) Promote crop diversity and farm resilience. Agriculture companies and research groups should continue to develop seeds and breed animals that are pathogen-resistant, but they should also emphasize genetic variation. Funding for local seed companies would ensure decentralization of resources and support heirloom seed lines, some of which maintain natural resistance to pathogens. Farms should consider adding tree buffers to create smaller, less connected populations of host crops and livestock available to transmit disease. The addition of trees also increases sequestration of carbon, decreases erosion, and serves as heat sinks, all of which help ease the effects of climate change, which in turn mitigates the spread of diseases that benefit from increased temperatures.

3) Fund alternatives to staple foods. Seed diversity is useful for outbreak mitigation, but how can governments decrease the risk of a major epiphytotic/epizootic or multiple bread basket failures that legitimately endangers food security? Organizations like the Alliance to Feed The Earth In Disasters (ALLFED) exist precisely to “identify various resilient food solutions and to help governments and companies implement these solutions to ensure people have enough to eat in the event of a global catastrophe. We focus on events, such as supervolcanic eruptions, which could deplete food supplies or access to 5% of the global population or more.” Resilient foods like mushrooms and seaweed should receive more research funding.

4) Decrease food waste…or make more food. Another way to counteract disease is to decrease wasted food or increase crop yield. Food waste is currently estimated at 30-40%, an unacceptable number that could be resolved with policy. Moreover, food production yields could continue to improve, thereby offsetting losses to disease. 

Predictions

Is there significant biorisk to America’s food production and supply? Clearly, yes, but these risks have been successfully dampened by a resilient natural environment, technological innovations that mitigate outbreaks and improve yields, and a decent amount of luck. Even so, if the COVID-19 pandemic has taught us anything, it’s that society should prepare for low probability, high impact tail-risk events. And like COVID-19, only a short series of mutations separates a lethal pathogen from a relatively harmless one. With all this in mind, will a US staple crop or livestock suffer catastrophic losses due to an epidemic or agroterrorism event by 2040?

I believe that the odds of a plant or livestock epidemic occurring in America are similar to the odds of a pandemic, which are approximately 2% per year. However, it’s much easier to quarantine, treat, or cull crops and animals, so the odds that an outbreak reaches the level of an epidemic are lower, perhaps 1% per year. Given a timeframe of about 18 years, odds of an epidemic would be around 17% (1-(.99)^18). In my opinion, this kind of risk is worth mitigating.