Annalisa Hultberg, Extension Educator food safety
What are the risks with animals?
Cats are often welcome farm pets,
but should not be allowed to roam in the growing area
Image: Produce Safety Alliance
Fresh fruits and vegetables are grown in soil, under the sky and near both wild and domestic animals, so there is always a risk of contamination from bacteria, viruses and parasites that can transfer to your fresh produce from these animals and their feces. Virtually all animals can carry human pathogens. Large numbers of animals means more risks because they produce large amounts of fecal matter; this could enter fields through run-off, contaminated irrigation water, airborne particles, direct deposit or insects.
Animal fecal material can contain bacteria like Salmonella, E coli 0157:H7 and Listeria monocytogenes that can make people sick with serious illness and complications, especially the young, old, and people with compromised immune systems. Therefore preventing contamination of the produce with feces in the first place is the goal.
"Co-management" protects wildlife and food safety
Animals are a very important part of the farm and farm environment. Food safety does not mean complete exclusion or elimination of any wildlife habitat or removing any animals from the environment. It just means using basic practices to keep domestic and wild animals out of the growing area as possible, and implementing some thoughtful processes about what to do when you encounter their feces in the field.
Here are some things to consider during the harvest season to avoid contamination from animal sources. Train your employees on these topics and include this information in your food safety plan policies.
Consider location before planting
Avoid planting produce near where you know animals tend to congregate, such as a path to a stream or directly under where birds often perch. If you pay attention, you will notice patterns in the times and locations of animal intrusions. Don't plant under an electric line, for example, as they often have birds perching on them. If birds regularly roost on a trellis, be very careful with the produce on and right below the trellis, as it might be more likely to have bird feces on it.
Bird feces is a common way that crops are contaminated with Salmonella. A recent outbreak in Wisconsin at a produce farm was traced back to a large number of migrating geese, and farm workers not being attentive to the amount of bird feces on the produce. At least 7 people were sickened at farmers' markets from this contamination.
While eagles roosting is a beautiful sight, produce grown under this tree,
(or equipment stored under it) might be more likely to have bird feces on it
Image credit: Pixnio creative commons
Of course birds of prey like raptors can control mice, voles and other unwanted pests on the farm. If you have perches for these birds, make sure that you look below the perch and don't harvest anything with visible fecal contamination. Consider locating the roost away from produce that will be consumed raw like leafy greens, tomatoes or melons.
Look for evidence of animals during harvest and use a buffer zone
One of the most important things you can do to avoid animal-based contamination of your produce is to teach your harvest crew that they should not harvest produce with visible fecal contamination. This contamination cannot be adequately washed off in postharvest washing. Bacteria are microscopic and often stick to the produce exterior or folds, stem scars or injuries and are not fully removed with washing. Bacteria will grow exponentially in storage if given the right conditions, potentially spreading to other produce.
Would you harvest these strawberries?
Source: FDA
If fecal contamination is present in the field, like this deer scat, do not harvest the produce that has been contaminated directly. You will need to assess how far away from the scat you want to make a "no harvest" buffer. Here are some considerations about how big to make the "no harvest" buffer:
- What size is the fecal contamination? If it is small, like this scat, you can likely remove it, and then just move out perhaps a foot or two to harvest. If it is large piles, the zone will be bigger.
- Is it dried, or fresh and wet? Wet, fresh feces will spread more readily.
- Has it been raining, and therefore could it splash up onto the produce?
- Is it hilly or flat? If it is hilly, runoff might move the contamination further.
- Is the produce staked/trellised, or on the ground? Will it be eaten raw, or cooked?
If you are working with many people in the field, use a flag to indicate a large amount of feces or other signs of animals. This will let the harvest crew know to avoid the area.
Once you remove the feces, harvest can proceed. You do not need to take that area out of production likely, but just do your best to reduce the potential for spreading the contamination by removing it from the field.
What animals are you dealing with?
Knowing what animals you are working with is the first step in keeping them away from your produce. Your actions to keep rabbits out of your field will be different than measures you take to keep deer out. There are online track and scat ID sites like the
Internet Center for Wildlife Damage Management.
Different scat from different animals
Image credit: Internet Center for Wildlife Damage Management
Records! Record when and where you find large amounts of feces or tracks or actual animals on a log sheet. Many animals are seasonal and your records will help you remember when they are present. This will help you see patterns of the animals and therefore plan your actions accordingly.
Exclude or deter animals from entering the growing area
Wild animals like deer, rabbits and gophers can carry pathogens on their fur, saliva and feces and through their urine. Of course they also nibble produce, reducing the amount of product you will have for sale. Dogs must be trained to run on the outside of the growing area, and to stay out of high tunnels and packing sheds. This is especially important now, when there is lots of produce with the edible portion present that can be contaminated by dog hair and feces. Remind visitors to leave animals at home.
A dog is a great addition to any farm, but should not be in the growing area
Image credit: Michele Schermann
Fencing is expensive, and not the best answer for all farms, but one of the key strategies many farmers use to exclude animals like deer from high-value crops. There are many different fencing types.
This MN DNR program offers a cost-share to help pay for the cost of the materials needed for exclusion fencing if you can show loss from wildlife.
Deer along a deer fence
Image credit: Produce Safety Alliance
Kitty as rodent control?
Cats should not be welcomed into a packinghouse or field as rodent control, since cats can carry
Toxoplasma gondii, which can cause severe illness including blindness, miscarriage, and death. Use unbaited traps in packsheds (such as a
Tin Cat trap) to trap mice. Remove anything that might be attracting mice into the packingshed, mow and weed-whip along the edge of the packingshed and remove harborage like stacks of lumber that rodents can hide in. If you choose to, you can use poison bait traps outside the packshed to trap mice (for non certified organic growers).
Maintain field and fenceline sanitation to reduce rodent habitat.
These steps can go a long way to reduce the pressure that wildlife can put on your produce crop while reducing the potential for illness from contamination from their feces.
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