farmers should wait at least 24 hours after a rain or irrigation event to harvest their crops, according to a new study conducted by researchers at Cornell University and just published in a scientific journal. Wet soil from precipitation is more conducive to growth of bacteria, such as Listeria monocytogenes and E. coli, according to the study. The researchers tested a variety of fields throughout New York state and found that the chance of finding Listeria was 25 times greater immediately after rain or irrigation. Waiting just 24 hours, however, resulted in Listeria presence dropping back down near baseline levels. The U.S. Food and Drug Administration has reportedly suggested that farmers implement wait periods before harvesting produce after irrigating fields. The study was funded by the Center for Produce Safety and published in this month’s edition of Applied and Environmental Microbiology.

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  • pawpaw

    This apparently is why FMSA, on the section on irrigation water quality and testing, is suggesting that more research be done on this very issue before water-quality regs are finalized. There may be very cost effective ways to limit pathogen risk, such as using free UV light within sunlight. These need to be identified before more burdensome methods are required. And then trying to shake loose the dollars to implement such.

    For those farmers willing to wait one day before harvest, do they really need to be paying for water testing multiple times per season? Also, keep in mind for crops that are trellised therefore up off the ground, this delay after a rain event may not be needed, but could still apply after irrigation.

  • Cloud 9 Farm

    This is irresponsible reporting. We run a CSA farming business here and the members expect to pick up their boxes according to a strict schedule. Many drive a considerable distance each week. We cannot delay pickups just because it rained. Rain is frequent here so delays would become the norm. Chaos would result. We would lose business. Although not certified (a needless expense) we farm with organic practices and all natural methods so our soil tilth is perfect. There is no listeros or any other harmful germs in our soil because we have healthy soil that produces healthy food that makes healthy people. Your remarks should say industrial farmed soil is the threat but not healthy soils of small farms. Get educated!

    • nigel

      Wow, seriously? Your soil doesn’t have Lysteria because it is healthy? And too good to be certified? Sounds like your “soil” don’t stink.

    • a

      This article is just reporting the results of a study, it’s hardly irresponsible reporting… But that is a good point about organic farms and would be a great followup study.

    • JoJackthewonderskunk

      I gaurentee there is listeria in your soil. Expecially if you aren’t testing or monitoring it in anyway, There is a reason for certifications to show you are in compliance with NOP. If you are producing product you claim to be organic without following the rules as applied to organic…….

    • Tom Woodbury-Chef

      While I can appreciate the concern with logistics a CSA may face as a result of these findings, your concern with the responsibility of the reporting has me scratching my head. A journalists primary role is to share the inconvenient and uncomfortable things going on in the world. In this specific scenario, casting light on the biology of bacteria growth, primarily the need for water to multiply, and the corresponding decrease in bacterial presence in waters absence, is the most responsible thing a reporter can do. Ignoring these findings because they make your job more challenging is far more irresponsible.

    • Michael Bulger

      The top result for “Cloud 9 farm CSA” on google is a farm in Montana. This Cloud Nine farm is Certified Organic.

      In the last few weeks, there has been a troll hitting the comments sections of sites like Food Safety News and Food Politics with great frequency. This person is creating multiple Disqus accounts and using them to attack or mock the “food movement”. I suspect that is what is going on here…

      • LP

        Thanks for that Michael. I was so flabbergasted by the imposters comments. Now they may more sense as nonsense.

    • R. U. Cereus

      I’m sure your soil has even more Listeria if it is farmed with organic practices. I doubt your claims would hold up in court. Get educated my eye!

  • Keith Warriner

    One would assume if Listeria is in the soil then the irrigation or rain event simply mobilizes the pathogen to accumulate and grow in the standing water. It follows that the crop would therefore harbor the pathogen and there is no reason why it wouldent persist over a day. The broader question is what level of Listeria would present a risk and how much would be carried through processing. Would the Listeria outbreak linked to apples not have occurred if there was a delay in harvesting – think not.

  • LP

    What an interesting, responsibly delivered and educational piece this was FSN. CSAs could incorporate this newly learned study result to further thier cause without adding a single new input except time. And as for delays….well, if you are in area with frequent rain then perhaps one would allow for delays becoming the norm. No oxymoron intended. Everyone knows L mono is everywhere as are many many other “harmful” germs so it’s nice to know a small measure such as letting things dry out a bit can reduce contamination. I enjoy the comments on this site, and interested in hearing the voice of so many well educated and passionate people.

  • Julie

    Good to know! Now I will pay closer attention to the weather and skip shopping the farmers market if our local weather was rain the previous couple of days. My family’s safety is the most important thing. There will always be another market next week but my kids and elderly parents are irreplaceable.

    • Michael Bulger

      Farmers’ markets typically feature farms from a regional area. Often, a farm will be located many miles away from the market site. This is particularly true in city farmers’ markets. For example, NYC Greenmarkets require farms to be located in an area that extends between 120 or 270 miles away (depending on direction of travel).

      Long story short, if it rains at your house or apartment it does not mean it rained at the farm. Unlike other sources of fresh fruits and vegetables, the farmers’ market will allow you to ask the farm directly about their weather and harvesting practices.

    • Iris

      Even on sunny days those farmers market vendors who show up with plump produce every week are certainly watering/irrigating each day it doesn’t rain a lot. The only way to be sure the farmer isn’t selling dangerous produce is to ask if the 24 hour dryout time is always occuring. Even then you can’t be certain so it’s a good idea to get a written receipt. You can easily jot down on the back a few notes about how your questions were answered. Then if the unthinkable happens to your family you can get back to the farmer and let them know about the problem. By your initiative the farmer might be able to prevent the same problem hurting other families. None of the farmers market food is inspected so it is up to customers to look out for everyone. Better safe than sorry as the old folks always said.