A pink plastic salad bowl of green lettuce

In 2018, an outbreak of Escherichia coli in romaine lettuce was linked to 210 cases of food poisoning, 96 hospitalizations, and 5 deaths. This was a tragic event in itself, but had far-reaching effects on the industry, as consumers became terrified of consuming lettuce. Understanding how E. coli infiltrates vegetables is the key to preventing contamination. Learn about the factors involved and steps toward E. coli prevention.

How E. Coli Contaminates Vegetables

The E. coli bacteria are found primarily in feces — particularly that of ruminants like cattle, but animals such as birds, reptiles, and insects can carry it as well. Typically, E. coli infects vegetables in two different ways: directly and indirectly.

Direct Contamination

Direct contamination with E. coli can occur when fresh manure is applied to a field — either before sowing or around the growing plants. Feces containing E. coli can also be deposited onto vegetable crops by birds flying overhead or animals grazing near the crop.

Indirect Contamination

Indirect contamination of E. coli in vegetables most often occurs via irrigation. In some cases, water runoff from a neighboring cattle farm might wash bacteria into your water supply or crop. In other cases, the water canal that irrigates your fields might have been contaminated by feces from wild animals or birds.

E. Coli Prevention

A dropper dripping clear liquid into test tubes

To prevent E. coli from contaminating vegetables, the most important thing is to regain control over your sources of water and organic matter. E. coli can be pathogenic in fresh manure when the bacteria are alive and active. Manure that has already been hot-composted and aged before use won’t generally cause a problem for your crops. This is because the E. coli will have been killed by the heat of the composting process and/or dealt with by the beneficial bacteria.

1. Develop An Effective Composting System

Making compost correctly provides a huge benefit to your crops and topsoil and prevents pathogens from being introduced into the soil. If you make your own compost (from plant matter, manure, or both), place your compost piles far away from row crops so that E. coli won’t contaminate your vegetables.

Following best industrial practices, make sure to turn your hot compost regularly and test the inside temperature with a thermometer. Turning and monitoring will ensure that the entire pile is heated to a temperature that will kill E. coli and other pathogens.

2. Separate Animals from Row Crop Areas

Most specialty-crop producers nowadays don’t have animals roaming around. However, if you have a mixed production model or operate next to a farm with animals, E. coli contamination of your vegetables is a real possibility.

In the case of a mixed-production farm, move animals off the field before planting and use physical barriers if necessary to keep them out. Communication with neighbors who raise animals is essential to make sure their animals, fresh manure, and manure-containing runoff don’t make their way into your fields and crops.

3. Apply Organic Matter at the Appropriate Times

As we stated earlier, organic matter is an integral part of soil management and crop health. But it must be applied at the right times and in the right way. To prevent E. coli from infecting your vegetables, add aged compost and manure to a field right after harvesting the plants and mix it in rather than leaving it exposed.

The time between manure application and harvest should be no less than 120 days or 90 days for crops that are protected by a pod or husk. This does not include any days in which the soil is frozen, as E. coli remains dormant at cold temperatures.

4. Test and Filter Irrigation Water before Use

Irrigation water is the other main source of E. coli contamination in vegetables and can bring pathogens from dams, channels, and groundwater located close to the surface. If you’ve already liaised with neighbors to stop the flow of contaminated water from farms, the next step is to have your irrigation water sources tested for bacteria like E. coli and Salmonella.

While only potable water should be used for irrigation, this is not always applied in practice — especially as California’s drought conditions make irrigation water harder to find. For specialty growers and row-crop farmers, in particular, it’s essential to invest in a water filtration system and use soaker hoses rather than overhead sprinklers to keep contaminants off the plants.

5. Wash Vegetables Thoroughly before Packing and Sale

The final aspect of E. coli prevention that you as a grower can control is the postharvest treatment of harvested vegetables. Postharvest processing should pay attention both to the washing of vegetables (with a bleach solution) to eliminate bacteria and teaching packers safe food-handling practices to prevent the introduction of bacteria after harvest.

In every stage of the growing process, workers should use separate tools, gloves, and equipment for working with organic matter and handling plants. The same applies in the packing house — keep equipment clean, sterilized, and separate from compost and manure to protect your harvested vegetables from E. coli.

Aftermarket Food-Handling Practices

From the moment your product leaves the packinghouse, further E. coli prevention measures are needed to keep your produce safe until it reaches the plate. While these measures might be out of your control, it’s still helpful to know what they are so that you can educate your customers about E. coli and the handling of vegetables:

  • Fresh produce should always be stored above raw meat in the fridge.
  • Wash vegetables thoroughly — leafy greens should be separated and washed one leaf at a time and root vegetables should be scrubbed under running water and/or peeled.
  • Leafy green vegetables can be washed with ½ cup white vinegar to 2 cups of water and rinsed, although this may affect the taste of the leaves.
  • Patting vegetables dry after washing may further help to remove bacteria.
  • Cook animal products thoroughly and never place cooked meat back onto a plate together with raw meat or blood.
  • Clean and sanitize chopping surfaces thoroughly, especially for foods (like salad greens) that will be consumed raw.
  • If you suspect E. coli poisoning, seek medical testing and treatment immediately.

Protect Your Vegetables from E. Coli with Solutions from Fruit Growers Supply

At Fruit Growers Supply Company, we understand that water is the prerequisite to agriculture, and that safe water is getting harder to find. To help California’s growers and producers, we have developed two important water-based programs that help to keep your produce free from E. coli:

1. Solar Irrigation Systems

We design custom-made, crop-specific solar irrigation systems that use soaker hoses for efficiency and filter all of the water before use.

2. Water Maintenance Program

For growers who have an irrigation system already in place, we offer a preventive water maintenance program to prevent E. coli contamination in vegetables

If you would like more information about how Fruit Growers Supply can help with E. coli prevention on your site, drop by or call one of our full-service stores in Orange Cove, Woodlake, Riverside, Porterville, or Santa Paula.

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