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Pre-Harvest Testing of Leafy Greens to Detect Pathogens is Self-Deception


The California Leafy Greens Marketing Agreement (LGMA) of California will introduce pre-harvest testing for produce grown in fields with "elevated risk factors".  The LGMA recognizes that proximity to a concentrated animal feeding operation (CAFO) represents a risk of applying STEC and Salmonella in contaminated irrigation water. Although protocols for testing have not been finalized, the release indicated that it is intended to collect and assay sixty stratified samples from a minimum of three pounds of produce per acre, 4-7 days prior to harvest.


According to Tim York, CEO of the LGMA, "new testing protocols are predicted to provide a 95 percent chance of finding a pathogen in the field even if only one percent of the crop is contaminated".  The updates to LGMA testing protocols are intended to convince regulators and customers of the safety of green produce.  There was no indication in the press release of the action that growers must take in the event of a positive isolation of a pathogen.  Will the crop be harvested? Treated? Ploughed back into the soil?  What preventive action will be taken to avert a reoccurrence? 


There is a general consensus among food scientist that it is not possible to test-one’s way out of a structural problem.  The fact that the LGMA is applying the test protocol only to "suspect fields" is a confirmation that the association is aware of the probability of infection. The assay protocol is a form of ‘pathogen roulette’ intended to create a false sense of security.


Fields adjacent to or in a location that could be contaminated by a CAFO should not be used for cultivation of green produce since it is inevitable that contamination will occur.  In the absence of a positive kill-step in processing, no amount of testing can provide an assurance of safety.


Subsequent outbreaks of STEC or salmonellosis attributed to green produce, will generate even greater demand for products grown in greenhouses under controlled conditions or from suppliers using vertical farming. This technology has profound benefits in terms of sustainability, quality, consistency, year-round supply and proximity to urban markets.