You, and your local restaurants, may be opting out of picking up heads or hearts of romaine lettuce, due to the spike in price that began in November 2022. Some blame inflation, but it is actually extensive crop loss and the resulting lettuce shortages that drove up prices across North America. To be more specific, salad crops are being lost to Pythium wilt and impatiens necrotic spot virus (INSV).

Did You Know? Salinas Valley, known as the “lettuce bowl of the world,” produces upwards of 70% of the lettuce in the United States. This region was at the heart of two lettuce disease outbreaks that led to massive crop losses.

Salinas Valley known as the lettuce bowl of the world
Salinas Valley is known as the “lettuce bowl of the world”

Pythium Wilt

Pythium wilt is a root rot disease which is caused by a fungus found in soils. Although 2020 was the first season it contributed to large crop loss, Pythium wilt was initially introduced to Salinas Valley around 2014. Given that this threat is relatively new to the lettuce industry, research is ongoing to identify causes and determine management strategies.

Yu-Chen Wang, a plant pathologist advisor at the University of California Cooperative Extension, discussed observing increased levels of Pythium wilt later in the season, when overall crop quality is lower, and during heat spells. This has led some to theorize the incidence of Pythium wilt is increased due to plant stress. This could also explain a potential interaction effect between the incidence of INSV and Pythium wilt, as plants infected with INSV may be more susceptible to contracting this root rot.

Impatiens Necrotic Spot Virus (INSV)

INSV is a virus transmitted by western flower thrips and impacts plant health in a variety of ways, including wilting, discoloration, necrotic spots, and potentially plant death. INSV has been present in Salinas Valley since 2006.

When asked about the impact excess heat and drought have on INSV, Kirsten Ann Pearsons – an IPM advisor at the University of California Cooperative extension – provided insight on how they can potentially impact the thrip population in different ways. After lettuce harvests are completed in the month of November, this source of food dries up for the thrips. That said, as wetter winter weather moves in, weeds provide an environment for them to continue to thrive. Given this, drier winter conditions may lead to a decrease in the thrips population over the winter.

Temperature also has a significant impact on the activity of thrips, and although the lower temperatures do not kill off thrip populations in the winter, it likely slows them down. As the average temperature in the valley has been increasing, it is potentially contributing to more activity and an extra generation of thrips being produced over the winter and resulting in possibly larger populations earlier in the season.

When asked if there are any other issues on her radar, Pearson said, “While pest and disease issues are at the forefront of our current discussion, I think the elephant in the room is water.” The Northern part of Salinas Valley sits on a critically overdrawn groundwater basin with drought exacerbating the problem. Although many growers are employing irrigation techniques to reduce water usage, the lack of groundwater recharge will still become an issue if drought continues. Pearson added she is optimistic growers will find solutions no matter how the environment changes, as they are “some of the most resilient people [she has] met.”

A report published by California’s Environmental Protection Agency in November of 2022 examined the Indicators of Climate Change in California, including trends in drought, temperature, and precipitation. These trends are showing that droughts have been increasing in intensity and frequency. In fact, described by the report as “an emerging ‘megadrought’ era”, 2000 to 2021 marked California’s driest 22-year period over the last 1,000 years. The report also noted changes in the environment allowing invasive pests to establish themselves and further decreases in bumble bee and pollinator population as intensifying issues.

A potential solution to add resilience to the food supply chain is controlled environment agriculture (CEA). With the increasingly changing climate and unpredictable weather events, controlled environment agriculture is a tool to mitigate these risks and provide a consistent product, year-round. Additionally, leafy greens are the widest produced crop in indoor farming systems and so could be particularly advantageous in this situation.

Lettuce Grown in Indoor Farms

In January of 2022, the wholesale price of California-grown Boston lettuce being imported to Montreal (Quebec, Canada) was $1.10. By November of 2022, with crop loss in full effect, the price skyrocketed to $3.83 per head. Comparatively, the wholesale price of one head of Boston lettuce produced in Quebec greenhouses remained at a constant $1.80 throughout the year. For reference, in the summer of 2022, the average price of wholesale Quebec field grown boston lettuce was $1 per head. Although a product from a greenhouse is more expensive, the crop maintains a consistent high quality throughout the year, and is uncoupled from extreme weather conditions.

Figure 1 - Natural Gas Consumption

Although the total wholesale price remains stable for lettuce from greenhouses, there is variability in the cost to operate them throughout the year. Comparatively, the inputs to maintain the environment in plant factories is relatively stable. Figure 1 and Figure 2 (below) show the fluctuation in electricity and gas inputs required for a greenhouse and vertical farm operating in Quebec, Canada.

Figure 2 - Electricity Consumption

Over the year, the total energy consumption for greenhouses was found to be slightly higher than vertical farms due to higher heating costs in the winter, although not by an extensive amount. This shows a potential advantage of vertical farms of greenhouses in more northern climates.

Resilience and Reliability From CEA

The spread of INSV, which carry thrips and Pythium spores in fields, are largely caused by uncontrollable events. Although it is possible to employ methods to reduce the potential of spreading, it is impossible to completely eliminate the causes of these diseases from the environment. This is where controlled environment agriculture offers another advantage in maintaining reliable harvests.
Biosecurity is a high priority in closed farms and reduces the potential for pests to infiltrate the environment and the threat from climate events is largely eliminated. A prime example is Fusion Farms keeping their farm operational during a devastating hurricane in Puerto Rico, with the use of a diesel generator to power lights.

Even if crop loss did occur in an indoor farm, the flexibility of production adds another layer of resiliency. Few climates allow for year-round outdoor cultivation, and harvests are usually limited to a few months of the year. If crop loss happens late in the season, there are no opportunities to produce another harvest. In closed environments, if a crop is lost due to disease issues, the system can be cleaned and immediately restarted with a new crop. Although it should be noted that generally, lettuce grown in fields is often grown longer for larger heads, compared to closed production which focuses on younger crops.

In conclusion, with increasingly adverse climate conditions in many areas of the world farmers will be faced with ever increasing challenges. Controlled environment agriculture provides a means of production decoupled from pests, climate events, and seasonal variation. With the technology deployment, the leafy green supply chain can be bolstered for the years to come.