Are rodents and bunnies nibbling your zucchini more than usual this year?

Annalisa Hultberg, Extension Educator, food safety

In periods of prolonged drought, you might be seeing more nibbles, chew marks and other signs of animal intrusion in your produce fields. Animals are seeking water, just like our plants, in the hot and dry conditions. Some farmers and gardeners have been asking about the safety of eating produce with visible bite marks. Be careful with any produce that has visible signs of animal damage, as where there is chewing, there is potential fecal contamination that can cause illness. 

Pathogenic bacteria, viruses and parasites such as toxigenic E. coli or Salmonella that might be present in fecal contamination are the most serious risk posed by animals.  Saliva has also been shown to potentially carry pathogens that can make humans sick, though it is not well-documented or likely to be a primary vector. Feces and dried feces in dust are the primary way animals spread illness to humans via fresh produce.

Can you just wash the contamination off or cut around it?

If you are eating the produce yourself, you could choose to cut out the chew marks and eat the produce, and that is your choice and risk you are taking on for yourself. Cooking might reduce potential illness causing microorganisms. But, if you are donating or selling that produce to others, this produce cannot include any that have visible contamination on them, or that have chew marks. You do not know the immune status of the person receiving them, and they expect that that produce is free from illness - causing organisms.  The potential to cause sickness is just too great and is not worth the risk. 

Remember, bacteria are microscopic and stick to the produce exterior or folds, stem scars or injuries and are not fully removed with washing. While washing will remove visible soil, sand and big debris, it is not guaranteed to remove all microscopic bacteria.  

What if you see signs of animals in the growing field such as feces?

You will need to assess how far away from the feces 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. 

Strawberries near feces (FDA)

Know 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. 

Do your best to keep them out

While it is not always 100% possible, do your best to exclude or deter animals from entering the growing area, and remove things that might attract them in the first place, like tall weeds and grasses around the perimeter of the fence and rotting vegetables in the rows.

Use deterrents such as ultrasonic noise repellent, sprays, moving and shiny objects to scare animals, or traps. There are many options, and they all have varying degree of success, based on what animals you are struggling with.

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. 

Can I just use cats to keep rodents away? 

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).

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.