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Growing Grounds from California Garden

© SAN DIEGO FLORAL ASSOCIATION

These stories may not be published in any form or copied onto another media without written permission from San Diego Floral Association.

Reprinted From: May/June 2023 Volume 114 No. 3

Strawberries in California

Part Two

By John Blocker 

In 1987 California produced more than eighty percent of the nation’s strawberries. That same year countries around the world signed the Montreal Protocol, a treaty banning or limiting the use of chemicals that damage the Earth’s ozone layer. Ozone provides protection from harmful radiation from the sun to all forms of life. In 1991 the fumigant methyl bromide was declared an ozone depleter under the Montreal Protocol. Strawberry growers and all other users of methyl bromide would soon be required to scale back use and eventually cease applying it altogether. Without methyl bromide, strawberry growers feared their fields would host diseases, pest populations would explode, and yields and profits would crater, endangering the whole industry.

Eye and Nose Irritation

In 1988 about 1:00 a.m., residents along Gum Tree Lane in Fallbrook alerted emergency dispatchers that their eyes were stinging and their nasal tracts were irritated. During the night sheriff deputies asked more than 100 residents in the area to evacuate. Twelve acres of soil in a dormant strawberry field nearby had been fumigated earlier that day with a combination of methyl bromide and chloropicrin (tear gas). The grower was sterilizing the soil to get it ready for planting. At the time, it was thought that dogs had run across the plastic covering that contained the gas combo, puncturing the tarp in several places and allowing gases to escape. 

Two similar episodes leading to eye and nasal tract irritation occurred in San Diego County during the next 10 to 12 years, one at a smaller field of fewer than five acres in Leucadia and the other on a 10- to 20-acre hillside along El Camino Real in Encinitas. Both fields were fumigated with a combination of methyl bromide and chloropicrin prior to planting flower crops. I was the supervising investigator for these two incidents for San Diego County Department of Agriculture. The troubling part about these applications is that they appeared to have been made correctly, with all safety requirements followed. 

On October 12, 1997, a resident of a mobile home park in Ventura County adjacent to a strawberry field worried about the fumigation plans that were about to commence. The resident related his fears to a San Diego Union reporter. “The pesticide is highly toxic,” he said. “Almost every afternoon wind from the ocean blows across the field and into the park. I don’t think they know what it will do or how much gets into the air.” 

Methyl bromide has become the poster child for agricultural-residential conflicts, said Veda Federighi, spokeswoman for the California Department of Pesticide Regulation (DPR), to the same San Diego Union reporter. “On one hand, farmers say they can’t live without it. On the other hand, people are saying they’re getting sick, and we have to get rid of it.” 

The Complications of Soil Fumigation

Incidents causing respiratory irritation sporadically occurred around the state after fields were fumigated. DPR initiated new safety measures. The requirements that growers must follow when using these chemicals became pages long, and buffer zones were expanded up to 250 feet.

We all know that wind can cause a pesticide to drift offsite. In the 1990s EPA found that spraying in no wind can also be a problem, especially in large agricultural fields. A certain amount of a spray application forms very light aerosols. A light breeze will disperse these aerosols. If there is no wind, these aerosols remain airborne near the site. If the air is still for a time, these aerosol pockets can rise to toxic levels. EPA now recommends that wind speed be at least three miles per hour when pesticides are applied.

This same principle applies to applications of fumigants made under plastic tarps. After the fumigant is injected into the soil, the tarp keeps the chemicals contained and at a concentration high enough in the soil to kill soil fungi, weeds and nematodes. Over time, the chemicals slowly seep through the covering and into the air at very low concentrations. If there is wind, the fumigants are blown offsite and dispersed to be broken down naturally.

If there is no wind, these gases stay at or near the site and build up over time. Chloropicrin (tear gas), causes eye irritation at extremely low levels. Along the coast during Santa Ana wind conditions, not only is it hot, but wind can die down for long periods, especially at night. Also, inversion levels can drop to a few hundred feet, keeping the chemicals concentrated near the ground. 

On August 31, 1988, the day the fumigation was made on Gum Tree Lane in Fallbrook, Palomar Airport began measuring wind speed at 3:00 a.m. The wind speed remained at zero mph until 6:00 a.m. when it quickly accelerated to six mph. Similar wind conditions most likely occurred in Fallbrook. I remember that the incidents in Leucadia and in Encinitas occurred on hot days during Santa Ana weather conditions. Stationary, still air was most likely a contributing factor for these incidents.

Finding a Substitute for Methyl Bromide 

Field trials for fumigants to replace methyl bromide did not begin in earnest in San Diego County until about 2004. Metam-sodium, a fumigant used for smaller soil parcels, was tested. The chemical did not disperse through the soil evenly, and the application process was prone to dangerous spills. Chloropicrin was again tried singly, not in combination with another fumigant. Results were unsatisfactory. 

Methyl iodide was thought to be the holy grail, the chemical that could simply be substituted for methyl bromide and achieve the same crop yields—if it could gain registration. Pesticides must be registered with both the federal Environmental Protection Agency and the California Department of Pesticide Regulation (DPR). When field trials showed that methyl iodide was effective, the fumigant was registered—but the registration was highly controversial. Many health experts believed methyl iodide was unsafe to use. DPR received more than 53,000 letters opposing registration and was sued by activists who believed the data was not properly evaluated. Arysta LifeScience, the maker of methyl iodide, dropped its application for registration just before a court ruling was to be given. 

A substitute for methyl bromide was reintroduced—1,3-dichloropropene (1,3-D), also called Telone TM. 1,3-D began its development as a soil fumigant in 1956 around the same time methyl bromide and chloropicrin were introduced. 1,3-D kills the same range of pests as methyl bromide: nematodes, insects and weed seeds. In strawberry fields, it is used in combination with chloropicrin as methyl bromide was, although it is used without chloropicrin for many other crops. This pesticide now is the most heavily used fumigant in the state in California. 

Ag/urban conflicts continued, however, when 1,3-D combined with chloropicrin was substituted for the methyl bromide/chloropicrin combination. New safety requirements will be implemented in 2024. Totally impermeable plastic tarps will be required for many applications depending on the amount of fumigant used. Buffer zones in certain cases will increase to 300 feet. Safety requirements continue to be pages long. 

Since 1991, when methyl bromide was listed to be phased out, the strawberry industry searched for alternatives to produce their crop. An alternative has been found, but it appears to instigate conflict as well. The use of chloropicrin is essential to obtaining high yields in strawberry fields. The active ingredient of tear gas, chloropicrin, causes eye and nasal irritation at extremely low levels. Until a substitute for chloropicrin is found, the ag/urban conflict will remain difficult to mitigate. 

Methyl bromide’s use on strawberry fields was finally banned in 2015 to protect the ozone layer. Interestingly, a look at the 2021 crop statistics shows that strawberry production is still high at over 20 tons per acre, a level equal to years when methyl bromide was used.

© SAN DIEGO FLORAL ASSOCIATION and © John Blocker.
These stories may not be published in any form or copied onto another media without written permission from San Diego Floral Association.