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Statistics against desert vegetable E. coli 0157 outbreak

It is always a nervous time when the Far West vegetable industry shifts production in the fall from California coastal valleys to the desert Yuma/Imperial valleys.

Prices and a smooth transition from the summer to winter crop to meet demand are normal concerns. This year a new apprehension was added to the mix; E. coli 0157.

Two major E. coli outbreaks in the early fall of 2006, one linked to spinach production on the California central coast and another traced initially to lettuce served at Taco Bell restaurants in the Northeast have desert growers justifiably concerned. Another one impacting them could have a devastating effect on prices.

And desert vegetable producers have reacted cautiously in the wake of the outbreaks, putting in place added water testing safeguards to prevent an outbreak in desert crops, according to Jorge Fonseca, University of Arizona vegetable specialist stationed at the UA's Yuma Agricultural Center.

Fonseca told growers and PCAs at the 17th annual Desert Vegetable Crops Workshop in Yuma, Ariz., recently that even though most of the major vegetable producers in Salinas also are the major producers in Yuma, there are some significant differences in production practices that may reduce the chances of an E. coli 0157 outbreak in the desert.

However, the best thing desert vegetable producers have going for them is time. According to the Food and Drug Administration, 80 percent of the E. coli outbreaks associated with fresh produce occur from August to November. Desert winter vegetable production basically begins in November and extends until early spring, when it transitions back to the Salinas area in California.

Nevertheless, Fonseca said desert growers are taking no chances. Since water for irrigation and use in packinghouses is believed to be a carrier of the E. coli 0157 strain, at least two Yuma labs are set up to sample water for microbial content.

“Growers here do not anticipate a problem, and they want to play it safe to make sure there is no problem,” said Fonseca, who has visited the Salinas area where the E. coli 0157 problem is believed to have originated, and has detailed some significant differences which or may or may not preclude E. coli 0157 from becoming a problem in the winter vegetable producing areas.

Some of these are:

  • Wild animals, specifically feral pigs, were implicated in the Salinas outbreak. Wild animals are not as big an issue in Yuma as in Salinas. There is a greater population of migratory birds in the desert than in Salinas. However, E. coli 0157 is found only in warm-blooded animals. Almost 90 percent of E. coli 0157 outbreaks have been traced to undercooked ground beef.

  • Vapam is widely used in Salinas, but not in Yuma and this may have an impact on E. coli 0157. Fonseca will be researching this issue.

  • Phosphoric acid is widely used in Yuma, but not in Salinas. It is used for treating pesticide spray water as well as a fertilizer.

  • The sources of irrigation and wash water are definitely different. Yuma gets its water from the salty Colorado River. Salinas's water is from wells. Regardless of the water source, water quality impacts microbial buildup, added Fonesca. Use the best possible water for crop sprays and irrigation.

  • High levels of nitrogen may have an impact on E. coli levels. The more N, the more young tissue there is vulnerable to E. coli contamination.

  • The final irrigation is critical to microbial buildup on lettuce. The longer the distance between the last irrigation and harvest, the higher the microbial buildup is on leafy vegetables.

  • Humidity is much higher in Salinas during the growing season, averaging 80 percent. In Yuma it is never more than 60 percent in the winter. There is a sharp decline in E. coli 0157 reproduction when the humidity is less than 60 percent.

  • Soil temperatures are as much as 20 degrees lower in Yuma during the vegetable production period than in Salinas and may impact E. coli reproduction.

Fonseca will continue researching these differences. However, he said just because statistically, there seems to be less chance of an E coli outbreak in leafy winter desert vegetables, it is better to err on the side of caution than to think what happened in Salinas could not happen in Yuma.

He said desert growers are not taking what may be good luck for granted and are monitoring water and other factors closely.

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