Fresh Produce Safety Includes Small Acreages and Home Gardens

Kurt D. Nolte and Stacey R. Bealmear
Yuma County Cooperative Extension, University of Arizona

The nation’s produce industry is in the crosshairs of the public health surveillance system following recent E. coli outbreaks, including an incident possibly linked to a Yuma area field. Most of us have heard about illnesses caused by E. coli and salmonella in meat or on leafy greens, and many assume that these incidents are contained to supermarket products. Surely concerns regarding fresh produce safety can't turn up in home gardens or in road side stands. Or, can it?

The number of homes growing vegetables will jump more than 40 percent this year compared with just two years ago, predicts The National Gardening Association, a non-profit organization for gardening education. W. Atlee Burpee, the world's largest seed company reported earlier this spring that vegetable seed sales are up 25 percent from a year ago.

And, in these tough economic times, American consumers are making an effort to save money by growing their own food. As most like the idea of growing their own vegetables, many do not know the specifics about fresh produce safety.

Significance of E. Coli O157:H7
Many pathogens cause problems with fresh produce. E. coli O157:H7, however, is of particular concern because only a few bacterial cells are needed to cause illness. The illness can progress quickly to cause severe consequences in susceptible people, particularly young children and the elderly. E. Coli O157:H7 is the Wile E. Coyote of pathogens. E. Coli O157:H7 can survive drought, refrigeration, even freezing, and can tolerate dry, acidic and salty conditions. Furthermore, it's remarkably virulent, being able to cause serious illness after minimal exposure. This is the pathogen that's has been implicated in most E. coli outbreaks. Animal feces, human feces, manures, and tainted water can all carry pathogens, especially E. Coli O157:H7. While most bacterial strains killed by reasonably high composting temperatures (130-140°F for several days), at least one strain of E. coli, E. Coli O157:H7 can't be reliably killed except by temperatures above 160°F.

Contamination by pathogens such as E. coli, salmonella and others occurs most frequently in manures, not in exclusively plant derived composts, and in fresh manure far more often than in mature, or composted, manures. However birds, dog, cats, reptiles, rodents and other animals or insects could add their waste to a home garden compost pile, contaminating otherwise pure vegetable compost.

Root crops and leafy vegetables have the greatest risk of infection from manure application to soil. They can also become contaminated through direct or indirect contact with pets, and either wild or domestic animals. While the bacteria do not appear to make these animals sick, the animals carry and shed the bacteria in their feces. Drinking and recreational water have been carriers in several outbreaks, supposedly from fecal contamination by infected animals or people.

Minimizing the Risk
The organism’s low infectious dose, survival under adverse conditions, and potential for extreme disease severity require successful prevention strategies. These strategies focus on reducing and eliminating the microorganism, both in the garden and in the kitchen. The following guidelines can greatly reduce the risk for E. coli O157:H7 contamination.

Garden Location
Locate a garden in the area with the least potential for contamination from fresh manure. It should be as far away as possible from animal pens (pets or livestock) and from manure or compost piles. If the garden is close to pens or manure piles, consider covering or roofing those areas to prevent rainfall runoff from flowing onto the garden.

Keep pets, livestock and wildlife out of the garden, especially during the growing season. This will prevent them from depositing fecal material onto garden soil and will exclude direct contact of manure with fruits and vegetables.

Water Use
Water is used not only to irrigate but to deliver liquid fertilizers and pesticides, if applied. To avoid E. coli contamination, use potable water for these purposes. If this is not possible, check the area around the water source. Is manure stored near the water? Is there a septic system near the water? Is manure applied to land near the water? Do livestock or wildlife have unrestricted access to the water? Are neighbors allowing contaminated runoff to enter the water?

It is important to prevent direct contact of potentially contaminated water with the fruits or vegetables you plan to harvest. The type of plant affects how water could be applied. If the edible portion of the crop is located above the soil, it is better to water with a drip system or a furrow or flood system than with sprinklers. This will limit direct contact between the water and the crop. Avoid using potentially contaminated water within 30 days of harvest.

Manure Management
Manure is an excellent fertilizer and soil conditioner. However, it is wise to not apply fresh manure to the soil in a fruit or vegetable garden. Even aged manure can have E. coli present. Composting manure properly will kill most E. coli. In order for a manure pile to be composted properly, the following requirements must be met:
• Mix the compost regularly. This is important not only for aeration but also to ensure that the entire compost pile has reached the required temperature.
• After composting, allow the compost to cure for two to four months before applying it to your garden soil. This allows the beneficial bacteria to kill disease-causing bacteria.
• Home composting of manure is riskier than commercial composting due to lower temperatures, greater temperature variability in the compost pile, smaller compost volumes, and inadequate temperature monitoring. Home composting plant materials alone (without manure) avoids potential pathogen problems.
• When using aged (not composted) manure, the following practices will reduce the potential for contamination:
o Never apply manure to growing food crops.
o For winter gardens, apply manure during the late spring, and mix it in. Spring application allows the longest period from application to harvest.
o Do not leave manure on the soil surface where it can have direct contact with the crop. Always mix it into the soil.
o Wait 120 days from manure application to crop harvest. This can be safely reduced to 90 days if the edible portion is protected by a husk, pod or shell.