Midwest Vegetable Guide - 2022 - 35

Produce Food Safety
Water should be tested for generic E. coli at least annually, or
as required by law or individual food safety programs. In
general, current guidelines allow an average of no more than
126 colony forming units of generic E. coli per 100 milliliters
(CFU/100 ml) of water intended for pre-harvest uses. Water
exceeding these parameters may require a corrective action,
such as water treatment, inspection and repair of the water
system, or extending the time between the last irrigation and
harvest. E. coli should be below detectable limits (typically
reported as ≤ 0 CFU/ml) for postharvest uses (product
cleaning, product cooling, etc.). Water quality laboratories
who use the approved FDA methods for testing have been
identified across the United States on a map which can be
accessed at go.uvm.edu/waterlabmap.
Growers covered by the Produce Safety Rule may also be
required to meet certain water testing requirements and
criteria. For more water sampling information and a summary
of Produce Safety Rule water testing criteria, growers should
consult Purdue Extension Publication, On-farm Food Safety
for Produce Growers: Microbial Water Quality Testing,
edustore.purdue.edu.
Irrigation Water
Pathogens can be introduced into irrigation water through
manure runoff from animal production facilities, sewage
runoff from treatment facilities or septic systems, or directly
from wildlife. Extreme rainfall, manure spills, or human
waste can increase the probability of contamination
occurring.
Ground water is the least likely water source to be
contaminated. Well water, when used directly, bears a
relatively low contamination risk, provided that the wells are
properly constructed and maintained. Wellheads should be
protected from contamination by elevating the wellhead above
ground level and using backflow prevention devices.
Surface water (such as ponds, creeks, and rivers) carries the
highest risk for contamination. Microbe levels in surface
water may change rapidly. Also, surface water cannot be
protected from contamination by wildlife, runoff, or other
potential sources of contamination. The following measures
may reduce the risk of microbial contamination in surface
water:
1. Construct ponds well away from apparent sources of
contamination such as livestock facilities and pastures,
composting pads, and sewage systems.
2. Fence ponds to prevent wildlife and domestic animals
from entering and contaminating the water and
surroundings.
3. Redirect runoff to flow away from the pond by building
a bank or channel.
4. Establish vegetation buffer zones around ponds to filter
runoff before it gets into the pond.
5. If irrigating from a creek or river, consider using a
settling pond. This will allow large particles that may
contain bacteria to settle at the bottom.
6. Communicate with neighboring livestock producers and
work collaboratively to maximize the distance between
livestock and water used for irrigation, spraying, or other
crop production practices.
7. Sediment and high microbial contamination loads may
be washed in by heavy rain. Remember to use caution if
using the water source after a heavy rain event.
Water application methods (drip, overhead, or furrow
irrigation), timing (how close to harvest), and vegetable types
(above, below, or on the soil) are also factors to consider.
These factors are often interrelated and have to be considered
in a combination.
Process Water
Water is used in many processing (or postharvest) operations,
including washing, cooling, top-icing, and transferring
product with flumes. Contaminated process water has the
potential to introduce and spread contamination throughout
an entire harvest lot. Process water that is not of adequate
microbial quality can easily transfer pathogens from
contaminated to noncontaminated produce.
To prevent cross-contamination, sanitizers may be added to
process waters. Sanitizers added to process water do not
" clean " the product as such. They merely sanitize the water
and prevent contamination from one piece of produce from
spreading to other pieces of produce.
There are a number of chemical and nonchemical (called
pesticide devices by FDA) sanitizers, such as chlorine,
chlorine dioxide, peracetic acid, hydrogen peroxide, ozone,
and UV light. The treatment chosen depends on various
factors, such as the type of produce, type of postharvest
operation, market requirements, etc. Seek sound technical
advice before investing in a sanitizing system. Any chemical
treatment used should be labeled for its intended use. See
table below for a list of EPA-registered products for use in
produce wash water. Growers who use sanitizers should be
prepared to monitor water pH, turbidity, temperature, and
other factors that affect sanitizer performance. More
information about chlorine-based monitoring systems is
available in Oxidation-Reduction Potential (ORP) for Water
Disinfection Monitoring, Control and Documentation,
University of California publication 8149, available from
anrcatalog.ucanr.edu.
Waste (manure)
Growers should use caution when using animal-derived soil
amendments. Biological soil amendments of animal origin
(BSAAO), those soil amendments such as manure, bone
meal, or feather meal, that are animal-derived may contain
human pathogens. Growers who use raw manure should
insure a lengthy interval between application and harvest. It is
Midwest Veg Guide 2022
35
http://go.uvm.edu/waterlabmap https://michiganstate-my.sharepoint.com/personal/phill406_msu_edu/Documents/Projects/Veg%20Guide/2022/Pre-crop%20material/edustore.purdue.edu https://anrcatalog.ucanr.edu/
Midwest Vegetable Guide - 2022

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