Download Brochure by WFA and CAFF:
Farming With Food Safety and Conservation in Mind
The co-management of food safety and conservation is covered in this brochure, by providing a helpful, science-based overview, outlining the low prevalence of food borne pathogens in wildlife, addressing conservation practices that can improve food safety, and offering a conservation-minded risk assessment strategy.
|Use of cover crops, compost, and other high-quality organic matter inputs encourage diverse soil microbial populations, which enhance suppression of E. coli pathogens in soil.
|| A grass strip just one yard wide can remove up to 99 percent of E. coli organisms from overland flow.
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Food borne illness linked to pathogens in meat, processed food, and produce has led to increased attention to food safety issues at all points along the supply chain, including the farm. Farmers can produce safe food without sacrificing responsible on-farm conservation measures, such as maintaining riparian habitat or other non-crop vegetation. Some corporate buyers, attorneys, marketers, and food safety regulators have suggested that such practices may pose risks on the assumption that wildlife may carry pathogens. On the contrary, evidence indicates that conservation practices and natural areas can often reduce pathogen risk while providing many other benefits, such as soil and water conservation, and habitat for pollinators and beneficial insects. Research demonstrates that wildlife have a low prevalence for carrying food borne pathogens. By using risk assessment strategies and explaining their rationale for management decisions to include conservation measures, farmers can more effectively advocate for their farming practices with buyers and food safety auditors.
How Did We Get Here?
Long before 2006, when E. coli O157:H7 made its way onto packaged fresh-cut
spinach—killing five people and sickening more than two hundred—food
safety auditors were on Salinas Valley, California, farms. The E. coli
outbreak was not a new phenomenon. Numerous such incidents had occurred
since 1993. But the deaths and large numbers of people sickened by the
produce in 2006 generated a strong response from the produce industry
and the Food and Drug Administration (FDA). Response to a broad FDA Consumer
Advisory effectively shut down spinach sales, causing large financial
losses in spinach and other sectors of the produce industry. The handlers
within the industry responded by creating the California (and later Arizona)
Leafy Green Products Handler Marketing Agreements (LGMA), which require
participating leafy greens handlers to ensure that their farm suppliers
are practicing Good Agricul- tural Practices (GAPs) that the Agreements
Unknown Culprit - Misguided Reaction
A series of investigations following the 2006 outbreak examined both the
field from which the spinach was harvested and the surrounding area. The
outbreak strain was identified in cattle and feral pig fecal matter, surface
water, sedi- ment, and soil samples collected during this investigation.
In general, cattle are a primary reservoir for E. coli patho- gens. The
pathway by which the pathogen may reach produce, however, remains unclear.
In the 2006 outbreak, investigators could not definitively identify the
pathway, but they theorized that irrigation water contaminated with manure
may have been problematic. Because the outbreak strain of the pathogen
was also found in non-native feral pig feces (known also as wild pigs,
wild hogs, wild boars, European wild boars, Russian wild boars, or razorbacks),
these animals were also discussed as potential sources of the pathogen
in the produce growing area. The California LGMA listed cattle, sheep,
goats, domestic and feral pigs, and deer as animals of significant risk,
though the low prevalence of the pathogen in deer populations led many
to challenge the appropriateness of including deer. It is important to
take samples directly from an animal, not from feces on the ground that
can be contaminated by other sources and/or deposited by an unknown number
of animals. For example, the report of deer feces found with E.coli pathogens
in Oregon strawberries was from feces on the ground. It is impossible
to determine whether a high per- centage of the deer were infected in
that region, or if the sample came from a few deer.
The 2006 spinach E. coli outbreak and the inclusion of deer in the LGMA
list of animals of significant risk increased concerns about wildlife
habitat near production areas. The resulting proliferation of food safety
metrics created a food safety arms race for marketing purposes. Growers
found themselves required to meet increasingly stringent food safety requirements
and to accommodate multiple food safety audits. In response to this pressure
from food safety auditors, growers trapped, poisoned, shot, and fenced
out wildlife. Natural habitat was denuded and conservation plantings—paid
for by public and private funds—were removed. The prevailing sentiment
was "Food safety trumps the environment," and farms on the Central
Coast of California were increasingly devoid of wildlife and any habitat
that might support them. Unfortunately, quite often the vegetation removed
was a critical component of sound soil and water quality conservation
as well as wildlife habitat.
As understanding has increased regarding the prevalence of pathogens in
wildlife and the pathways by which patho- gens may move, it has become
clear that the initial measures taken following the outbreak should be
reconsidered. The concerns regarding wildlife created by some food safety
metrics have been hard to dispel. At times these they have led to rigid
application of conservation-threatening metrics in crops that present
minimal to no food safety risk. Such a misguided focus on wildlife in
food safety regulation has led to the removal of conservation measures
that could actually benefit food safety, with little thought to the ecosystem
services and public health benefits these features provide.
Relative Food Safety Risk of Wildlife
Native wildlife species pose a low relative risk of carrying human pathogens
such E. coli O157:H7 and Salmonella (prevalence in wildlife
generally <3%). When wildlife share rangeland or water sources with
higher risk beef cattle, feral pigs, hog or dairy operations, it is probable
that contamination occurs, though this cross-contamination has not been
well demonstrated. The risk of extensive contamination from wildlife is
not zero—and will never be zero—but it is low. Despite this,
if popu- lation density in the growing area is high for a wildlife species,
steps should be taken to reduce wildlife activity, since the risk of contamina-
tion will increase.
Deer studies have found low prevalence of pathogens in deer fecal matter,
even when they share rangeland with cattle (which may have much higher
pathogen prevalence). Ongoing research has thus far found little evidence
to support the intense focus on these animals as a food safety risk. Many
growers already manage deer populations because the animals damage or
consume crops. Of greater significance than the loss of deer themselves
is the removal of their habitat. This habitat not only supports many other
kinds of wildlife, but also acts as a ‘natural filter’ that
provides us with clean air and water.
Feral pigs frequently share rangeland with cattle and consume cattle manure,
which may increase the odds that they will carry pathogens. Prevalence
data for these animals is scarce but indicates that they may carry food-borne
pathogens at a higher rate than native wildlife. Populations may be quite
high in some areas, and in this case control is war ranted. Non-native
feral pigs present a conservation challenge; therefore hunting and trapping
are common population control measures.
Rodents living in the field show a low prevalence of E. coli pathogens,
although some ground squirrels and deer mice have been detected with higher
levels of Salmonella and other food-borne pathogens. Non-na- tive rats
and mice found around farm structures can carry many types of diseases.
When rodents are in large numbers, or living near farm animal operations
and polluted areas, steps to reduce them may be needed.
Birds pose a greater food safety risk when they inhabit areas with high
levels of pathogens. Research has found increased levels of pathogens
in birds that frequent landfills, feedlots, dairies, cattle ranches, or
pig farms. Birds can transfer pathogens from these sites.
Flies can also carry pathogens from infected manure to crops, but they
typically stay close to manure unless drawn by other food sources, such
as honeydew secreted by an aphid infestation in a crop.
Reptiles and amphibians (such as lizards and frogs) can carry Salmonel-
la, especially when kept as caged pets. Emerging research in the Central
Coast of California is showing that there is a risk - albeit low - of
frogs in the wild carrying Salmonella.
General Advice for Animal Management
Rather than striving to eliminate all wildlife, optimize features on the farm to encourage habitat-dependent species to stay in their preferred natural environment and out of the crop.
Livestock are easier to manage than wildlife. Exclude non-draft animals from fields during the growing season, especially close to harvest time. Catch manure of draft animals.
Monitor crop fields for animal intrusion and designate a no-harvest zone if fecal matter is present, depending on the crop spacing and other features of the farm.
When there is unusually heavy wildlife activity in the field, use loud noises, sprinklers activated by motion sensors, scare balloons, food attractants placed in other areas, and fencing to discourage wildlife from entering the crop area.
To deter wildlife, place fences around the growing fields only, not around the whole farm. Fencing individual fields rather than the entire property allows corridors for wildlife movement.
Avoid removing vegetation in and around growing areas, especially plants used in conservation practices, established riparian zones, or other natural areas. Removal may increase pathogen risk and adverse impacts on public health.
Specific Wildlife Considerations
Deer: If deer are present in large num- bers, steps may be needed
to reduce entry, but removing habitat is counterproductive.
Feral Pigs: Hunt or trap feral pigs, or if they are continuously
present in large numbers, install a short hog wire fence. Habitat removal
will not effectively eliminate the animals.
Rodents: Control rodents near packing facilities, or
when there is a high popula- tion in the field, particularly when they
may have access to polluted areas or animal operations. Encourage predatory
hawks and owls by providing birds with roosts and habitats, especially
when ro- dent population density is high.
Birds: Birds could cause concern on farms situated near
operations where significant manure or pathogen-rich wastes collect (e.g.,
landfill and feedlots). Farmers should discourage birds from collecting
at these sites, and should dissuade them from moving into crop fields
from these sites.
Flies: Farms located very near operations where significant
amounts of manure accumulate should manage crop attractants (e.g., aphid
populations that generate honeydew) so they do not draw flies.
Amphibians: Maintain vegetated buffers between water
sources (where amphibians are likely to be more abundant) and crops to
provide a preferred habitat.
Why Soil Microbial Diversity is Important to Public Health
Cover crops and compost support diverse microbial soil populations by increasing the organic matter content of the soil. As microorganisms decompose these materials, they create humus. This complex organic material provides numerous soil health benefits, such as improved soil structure and water holding capacity, increased nutrient holding capacity, improved nutrient cycling and long-term carbon storage in the soil.
Soil management practices can increase or decrease plant and human pathogens in the growing environment. For example, manure slurries may create conditions that favor pathogen survival in the soil. Composted manure provides nutrients and organic matter with less risk of pathogen contamination, since pathogens are killed when proper composting methods are followed. In general, E. coli O157:H7 survives best in anaerobic, carbon- and nutrient-rich conditions, such as those found in the guts of ruminant animals, its natural host. Management practices that influence carbon and nutrient supply may influence pathogen survival. Use of cover crops, compost, and other high-quality organic matter inputs encourage diverse soil microbial populations, which enhance suppression of soil-borne plant pathogens through competition and lower survival of E. coli pathogens in soil. Food safety and public health require careful consideration of soil management strategies that may impact pathogen sources and survival.
Soil Management Considerations
Cover Crops and Compost: Use cover crops and compost to increase
soil organic matter and to encourage diverse microbial soil populations.
Composting Process: Ensure that all composted materials
have been produced following recommended practices.
Compost Recordkeeping: Whether mak- ing compost on the
farm or purchasing it from others, maintain or request records of the
process and the materials used to make it, the nutrient content and pathogen
test results for finished product, and the finished product storage methods.
Fumigation: Do not fumigate the soil for food safety
reasons. Rather than trying to kill all microbes in soils with fumigation,
optimize microbial diversity. This will increase competition with pathogens,
and may help reduce pathogen survival in the farm environment.
Raw Manure: Use caution in applying raw manure. Until more is known on best practices for safe use, avoid uncomposted manure or follow the National Organic Program regulations that require raw animal manure to be composted unless it is (a) incorporated into the soil not less than 120 days prior to the harvest of a product whose edible portion has direct contact with the soil, or (b) incorporated into the soil not less than 90 days prior to the harvest of a product whose edible portion does not have direct contact with the soil.
When compost is made correctly, there is little chance of pathogens persisting in the finished product. To reduce pathogen risk from composted manure and to decrease the likelihood of pollution, keep the following considerations in mind:
Bring compost to 131 degrees Fahrenheit for 15 days to kill pathogens with the heating process.
All parts of the compost must be heated quickly. If it takes too long to heat up, pathogens may develop resistance to subsequent heat treatment thereby allowing their survival.
Temperature should ideally arrive at the killing level within two days.
Aerate compost by turning it regularly (a minimum of five times), so high and low temperatures alternate; varied temperatures are more harmful to pathogens than constant temperatures.
Cover the pile with finished compost or a tarp to help ensure that all parts heat equally, so the edges reach killing temperatures.
Control moisture and carbon to nitrogen ratio (C/ N), as pathogen survival increases when these fall outside optimum ranges. Optimum moisture content is approximately 50 percent, and an appropriate carbon/nitrogen ratio is approximately 25:1 – 40:1. The C/N ratio is controlled by choice of materials added to the compost.
Test finished compost for E. coli O157:H7 and Salmonella. Commercial composters that follow best practice management make results available to their customers.
Take care not to re-inoculate finished compost with pathogens by using unsanitized equipment to move or spread the finished product.
Locate the compost site a minimum of three hundred feet away from waterways.
Divert clean surface water away from the composting site so it does not become contaminated.
Change into clean clothes and footwear after touching manure or compost, particularly before harvesting and handling food crops.
The National Organic Program offers additional guidance on recommended composting practices. See section 205.203: Soil fertility and crop nutrient management practice standard, found here: www.ams.usda.gov/AMSv1.0/nop.
Vegetation's Filtering Capacity
E. coli and Salmonella pathogens may wash into surface waters
and be carried with dust particles blowing in the wind. Grasses, vegetated
buffers, and wetlands can effectively decrease water-borne pathogens by
intercepting them as they move off the landscape toward surface waters.
Hedgerows and windbreaks can help filter air-borne pathogens. They also
support pollinators and other beneficial insects. Increased pollination
enlarges fruit set, and a third of our food supply depends on pollinators.
Predator and parasitic insects help to control pest insects. Greater biological
control of pests provides public health benefits by reducing pesticide
use and protecting pollinators, which are in decline worldwide.
A grass strip just one yard wide can remove up to 99 percent of E. coli
organisms from overland flows across rangelands by trapping fecal matter
and filtering surface flow water. Natural wetlands can filter up to 91
percent of E. coli organisms from water moving off rangelands. Vegetation
connected to settling basins can also significantly reduce pathogen movement.
The ability of vegetation in ditches and ponds to reduce pathogen movement
to surface waters, as well as nutrient, pesticide, and other contaminants,
depends on how much contact the water has with the vegetation and how
quickly it flows past the vegetation. Longer residence times remove more
pollutants. In crop production areas, ditches are often planted in grasses,
sedges, and rushes to help hold soil in place. The wider the ditches,
the slower the water will move, which allows more grass surface area exposure
and greater pollutant removal.
Hedgerows and windbreaks are also effective at reducing dust movement.
When cattle congregate along fence lines or under shade trees, they grind
manure underfoot into dust which may become airborne. Pathogen-contaminated
dust can also blow in from nearby farm animal operations. For every foot
of hedgerow/windbreak height, ten feet of modification occurs downwind;
a 30-foot tall planting will provide a 300-foot long wind shadow. Such
plantings also reduce pesticide drift and other types of particulate matter
air pollution, thereby providing important public health benefits.
Good Food Safety Protocol
Use risk assessment to optimize actions. Before planting crops,
assess fields for any food safety problems that may have arisen since
the last harvest. These could include new neighboring livestock or contaminated
water that may have, or might, flow across the production ground. Other
factors to consider include changes on the farm itself, such as a downed
livestock fence or an altered wildlife corridor. Just as diligent farmers
scout their fields routinely for insects and plant diseases in produce
fields, they should scout for wildlife and livestock activity on a regular
basis prior to harvest time.
Living systems always carry some risk. Minimize that risk by optimizing
the natural services provided by well-managed vegetation, soil, and water-
understanding that fostering healthy, balanced, agricultural systems offer
the most robust strategy to support public health. Co-management of food
safety and conservation on the farm can be attained. The information here
will equip growers to evaluate food safety risk factors on their farm
and thoughtfully manage to minimize them. A written food safety plan,
which describes and explains the farm's management practices, is an excellent
step toward avoiding food safety problems.
For More Information
• To read the scientific articles that support the advice presented
here, please see the following websites, or request a written copy using
the following mailing addresses:
• Wild Farm Alliance (WFA) – www.wildfarmalliance.org –
PO Box 2570, Watsonville, CA 95077
• Community Alliance with Family Farmers (CAFF) – www.caff.org
– PO Box 363, Davis, CA 95617 • For further help in addressing
food safety, see Family Farm Good Agricultural Practices (GAPs) and Standard
Operating Procedures (SOPs) at www.caff.org. • The most extensive
report on balancing food safety and environmental considerations is Safe
Co-managing for Food Safety and Ecological Health in California’s
Central Coast Region found at– www.wildfarmalliance.org/resources/Safe_&_Sustainable.pdf.
• For some of the latest produce safety research, see UC Davis Center
for Produce Safety http://cps.ucdavis.edu.
This brochure was written by Jo Ann Baumgartner of WFA and Dave Runsten
of CAFF, July 2011, and updated January 2013.
Disclaimer: This document provides guidelines and practical tools for
use by family farmers. It is intended as an educational resource and not
as technical advice tailored to a specific farming operation or as a substitute
for actual regulations and guidance from FDA or other regulatory agencies.
It is also not intended as legal advice. We will not be responsible or
liable, directly or indirectly, for any consequences resulting from use
of this document or any resources identified in this document. Wild Farm
Alliance and Community Alliance with Family Farmers are providing this
document to family farmers as an educational service.