December 15, 1999
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967

"In response to the "growers lament" in the last AgReview, I do figure my time and find that I'm making money on everything (I'm growing 30 different kinds of veggies and herbs) except for a few things. I'm breaking even on peppers, celery, and broccoli. However, I feel as though I've hit a price ceiling on those items, but still need to provide them for my customers. Other items like squash, pumpkins, tomatoes, melons, lettuce I am making huge profit margins on. It cost me 29 cents a pound to produce melons and I am selling them for 75 cents a pound. It makes a difference that they are delicious. People will pay extra to get an amazing product. Tomatoes also are excellent and people are willing to pay for them. But lets face it, though I think my broccoli tastes better then anything from CA, it's not head and tails better like my melons are. It should be noted that my business is very concentrated. I only direct market (except for melons), and only do veggies. This allows me to focus my energies, and profitability, in ways that growers who are more diversified can't."

"No question that the greatest profit margin on our farm comes in from the flower end, and it's true that many of the field crops that we grow are grown at a loss to provide consumers with the diversity we think they require in order to get them to come to our farmstand. My view is that the economy can be cyclical, and should the stock market have a big correction we vegetable farmers might find it more profitable to be able to produce food instead of ornamentals. Diversity is the bane of our existence because of the demands of management it makes upon us. But we need it because it protects our market by broadening it. Gasoline sales and convenience mini-marts have thrived because of the diversity they provide, and we farmers who retail will also survive as long as we can maintain our diversity."

"What types of manure spreaders are good for spreading light applications of compost uniformly on small fields - what types of manure spreaders should be avoided for this purpose?" Replies to the editor are requested.

(Adapted from an article by Dr. Trevor Suslow, Dept. of Vegetable Crops, Univ. of CA, Davis. More on this topic in coming months...)

Farming practices that emphasize the use of raw or aged animal manure, manure slurries or "teas", and animal manure-based compost play an important role in the recycling of organic nutrients and developing a rich soil structure. Due to the increasing frequency of outbreaks of food-borne pathogens, there is concern about a different type of recycling through our agricultural systems. The recycling of bacterial pathogens and protozoan parasites from animals to humans through water, soil and crops has created a serious challenge for producers, processors, and consumers of fresh produce. For example, during a single 1996 Escherichia coli (E. Coli) outbreak in Japan, 9 people died, 30 people were reported in critical condition, and a total of 8,500 cases were recorded. The suspected cause of the outbreak was salad, with sprouted radish seeds being the primary suspected source of the food borne contamination. Closer to home in Montana that same year, another E. Coli outbreak occurred. Leaf lettuces were the identified culprits. Affecting more than 70 people, this outbreak was associated with consumption of leafy red, green, and Romaine lettuce. Though not proved conclusively as the source, concern was raised for the potential risk of contaminated irrigation water or manure?amended soil.

To keep things in perspective, it is important to strongly emphasize that the number of cases of food borne illness known or suspected to involve fresh produce are extremely few, relative to meat and poultry sources. The majority of confirmed cases that involve produce are the result of poor handling practices at the food service or home consumer level. The frequency is increasing, however, and the increased consumption of uncooked fruits and vegetables elevated the risk of exposure because there are limited process controls available to protect the consumer.

Currently, much of the focus of developing on-farm prevention programs is on E. Coli O157:H7 and related toxigenic E. Coli. Growers and others directly involved in crop management must increase their awareness of the elevated risk and potentially severe (or lethal) consequences of infection of these bacteria from noncooked produce. Current information supports a very low probability of contamination, at the farm level, across the majority of domestic produce but the potential consequences of a single, rare outbreak are severe.

E. Coli O157:H7 is the predominant strain of a group of toxin-producing E. Coli. Common E. coli is an ubiquitous intestinal inhabitant. The toxigenic forms, such as E. Coli O157:H7 have been an increasing problem since first identified in 1982. Although far fewer cases have been recorded than of Salmonella cases, E. Coli O157:H7 is more hazardous, causing the life-threatening condition Hemolytic Uremic Syndrome (HUS) which results in acute kidney failure. An additional risk feature associated with E. Coli O157:H7 results from the very low number of contaminating cells required for infection. Estimates, based on epidemiological evidence from recent outbreaks, vary but it is generally agreed that less than 10 bacteria per gram of food may be sufficient to cause infection in sensitive individuals. The population sector most at risk are the very young, the elderly, women during pregnancy, and immuno-compromised individuals. With so few bacterial cells necessary, growth on infested produce is not a requirement for human infection, as with most other pathogens. Therefore refrigeration of harvested produce during transportation and distribution is not a sufficient control for this group of pathogens. In addition, due to the very low infective dose, absence of detection is not a foolproof assurance of safety. Screening of harvested produce is not a practical approach to control.

E.coli O157:H7 has been found in reservoir and recreational water and in water sources used for overhead irrigation of vegetables. It has been detected in the feces of many animals including dairy and feedlot cows, poultry (especially chicks), lamb, piglets, children, pets, deer, rabbits and waterfowl. Dairy herds have been targeted as presumptive sources of E. Coli O157:H7 that may find their way on to produce through aerosols, surface water, and incompletely composted manures. E. Coli O157:H7 has been shown to persist in drying manure and to be present in incompletely composted dairy and feedlot waste. Persistence in manure amended soils is not well characterized and the duration of soil survival, transfer to, and potential colonization of above ground plant tissue, such as leafy lettuce, are largely unknown for this and related toxigenic strains.

The transference of E.coli O157:H7 from these sources to the harvested portion of fruits and vegetables may seem logical and predictable but little documented evidence for their environmental behaviors is available. This information will be critical in the development of guidelines for the safe handling and application of animal manure's to farm land, particularly for vegetable production systems. Outbreaks of both Salmonella and E. Coli O157:H7 are often the result of cross-contamination from animal (meat, eggs) sources during food preparation in food service establishments or in the home. However, documented cases and research reports of these pathogens on fruit or vegetables directly from the farm source extend the need for prevention and control programs from "field to fork".

What makes E. Coli O157:H7 and other related strains of E. Coli a threat to humans is their acquired ability to produce toxins and other virulence factors In addition, recent research has shown that this strain is more resistant than standard E. Coli to dry conditions, freezing, and acid conditions. Environmental stresses that inactivate conventional E. Coli are much better tolerated by E.coli O157:H7. Although peak temperatures reached during the composting process, 140 degrees F sustained for 3 weeks, are sufficient to kill these microbes, the uniformity of application of the composting process has not been adequately addressed or observed in practical applications.

The best approach, at this time, is a comprehensive prevention and on-farm risk management program. Sanitation and proper worker hygiene during harvest and postharvest processing are important additional components of a comprehensive program. Until more specific information is available about the environmental dissemination and persistence of E. Coli O157:H7 and other key pathogens, common sense approaches to on-farm microbial safety will go a long way to minimizing the risk of food borne illness. Some farming practices that were considered safe in "the good-old-days" are a current liability. Some practices developed as a source of supplemental organic nutrients and pest control (foliar applied manure slurries) seem ill-advised.

Like most E. Coli, type O157:H7 is sensitive to chlorine, ozone, and other disinfectants provided there is physical contact with the bacterial cell. Preharvest contamination-prevention programs and postharvest sanitation are key tools to preventing outbreaks. On-farm prevention programs should include basic sanitation practices for all harvest containers, contact surfaces, and postharvest washing. Washing fruit and vegetables with clean, domestic (potable) water removes many undesirable surface contaminants. Although not an assurance of complete safety, disinfection is an essential process to include any time produce intended for commercial sale is washed.