Animals entering fruit and vegetable fields now are potential food-safety problems rather than just cropdamaging nuisances. But how far should growers take their exclusion efforts?
Some industry groups already require specific practices to address contamination problems from birds, frogs, deer and other animals, both wild and domesticated.
California’s Leafy Greens Handler Marketing Agreement grew out of the 2006 E. coli outbreak in spinach linked to nearby animal populations, and Florida’s tomato industry adopted its own guidelines in 2008.
“The vast majority of production is safe,” says Reggie Brown, manager of the Florida Tomato Committee in Maitland. “But we can’t grow crops in a bubble.”
Most tomato fields are fenced or diked to prevent crop contamination and damage from large animals, Brown says. E. coli outbreaks in other parts of the country have been traced to mammalian intrusions.
The pathogen also appears in birds, but preventing avian intrusions is much harder, he says.
Included in the tomato guidelines are preharvest scouting for any potential foodsafety risks, and training harvesters to leave behind any fruit that’s contacted fecal material.
Where scouting turns up suspicions of animal intrusion, growers are to set aside a reasonable no-harvest buffer zone, Brown says.
The produce industry as a whole needs practical, science-based risk-assessment knowledge when it comes to food safety, he says.
Science is the key
Science is the key to determining effective management practices, says Michelle Danyluk, assistant professor of food science and human nutrition at the University of Florida’s Lake Alfred Citrus Research and Education Center.
“Not all animals are created equal, and not all animals carry the same risk,” she says.
Likewise, different crops may vary in their susceptibility; strawberries are grown closer to the ground than staked tomatoes, and harvests of fresh-market citrus may more stringently exclude dropped fruit than citrus intended for juice.
Food-safety research so far has lagged behind industry and consumer concerns about the risks from animal intrusion and contamination, Danyluk says.
Concrete data on where risks lie and the degree of those risks should begin appearing within the next three to five years.
Unanswered questions include what the appropriate buffer zones around a point of animal intrusion are for different crops and how long different pathogens persist in the environment.
Others, she says, might be whether practices such as the summer flooding of fields in South Florida to prevent erosion pose a foodsafety risk, or how many frogs or feral hogs in the vicinity create a risk.
Scientific data lacking
After the California spinach scare, many growers cleared a large zone around their fields, despite competing concerns for environmental stewardship in riparian areas. But solid scientific data showing a related reduction in food-safety risk is lacking, Danyluk says.
For now, the bottom line is risk awareness and taking practical steps to minimize animal contact with food, she says.
Most importantly, keep detailed records of all preventive and corrective actions. Focus on what’s reasonable, says Keith Schneider, associate professor of food science and human nutrition at the University of Florida in Gainesville.
“There’s no way to exclude birds or little bunnies,” he says. And fencing isn’t 100 percent effective against deer.
Domesticated animals, however, are much easier to control.
“We know that cattle shed Salmonella at a certain rate and carry E. coli,” Schneider says. Fence off cow pastures or fence produce fields near cattle operations.
Other basic steps include steering clear of using goats for weed control. Don’t bring farm dogs into your fields, he says.
Focus on high-risk items
At Straughn Farms in Waldo, birds attracted to the company’s blueberry fields are a primary food-safety and crop-loss concern.
Scare cannons are the main weapon in the battle to keep birds out, says Terra Hess, food safety director.
As part of the preharvest routine, the company conducts block inspections to make sure no fecal matter has touched the crop.
To reduce that possibility, no dogs or chickens are allowed on the premises, and fields are fenced to discourage deer and turkeys, Hess says.
Wells that are inspected regularly supply all spray water, avoiding potential risks in drawing water from retention ponds that might attract wildlife, she says.
Bodies of open water are more likely to pose a risk than well-constructed deep wells, Brown says.
Keeping wildlife—especially ducks and other waterfowl—away from water sources is a tall order, Danyluk says.
Risks also depend on the contaminant level and the water’s agricultural applications, Brown says.
Water that comes in contact with the edible portion of the crop should be considered a greater potential risk, he says. His group’s tomato guidelines require using only potable water as a spray material.
That’s much less costly than the loss of confidence a company or industry might experience in the wake of a food-safety outbreak, Brown says.
Still, more research is needed to address questions about water use and standards, he says. For instance, how does solar radiation affect pathogen levels and risks in retention ponds?
Other questions include whether overhead irrigation is safer than drip or furrow irrigation, and whether some potential risks depend more on timing than the practice itself, says Michele Jay-Russell, a researcher for the Western Institute for Food Safety and Security at the University of California, Davis.
Risks may concentrate just before and during harvest periods, perhaps allowing some leeway the rest of the year, she says.
Whether pathogens persist in the soil or can be taken up by plant roots—and whether those pose realistic food-safety risks—remains unknown.
“There’s not an easy answer,” Danyluk says. But taking reasonable steps to manage animals that can be a source of pathogens will go a long way.