Protecting Your Harvest from Vertebrate Pests - UNL CropWatch, Jan. 18, 2012

Protecting Your Harvest from Vertebrate Pests - UNL CropWatch, Jan. 18, 2012

Area around bin

Rat trail by a grain bin indicating rodent control measures are needed to protect stored grain. (Photo by Robert Timm)

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This is the first of a three-part series on the impact and control of vertebrate pests in stored grain.  See upcoming issues of CropWatch for:

  • Non-Toxic Strategies to Manage Rodent Damage to Stored Grain
  • Use of Toxicants to Manage Rodent Damage to Stored Grain

Rodent droppings in corn

Rat droppings in stored corn. (Photo by Kurt VerCauteren)

January 18, 2012

Potential Impacts of Rodents on Stored Grain

With your crop harvested and in storage, you may think that a hard summer’s work is over, but it isn’t. You need to protect your earnings from Norway rats (Rattus norvegicus) and house mice (Mus musculus). These rodents threaten stored grain by direct consumption, damage to grain storage structures, and by contamination through defecation.

Grain Loss by Direct Consumption

Adult rats consume about 3 oz of food per day or about 50 lb of grain per year. While stored grain does not provide the complete nutritional balance they require, it can make up a significant portion of their dietary needs and sustain them until other foods become available. Mice consume 1/10 oz per day or about 2 lb of grain per year. Although direct consumption of grain by rodents is estimated at 1% of the total amount in storage, severe cases can result in substantial profit loss.

Grain Loss by Structural Damage

Rodents threaten grain by gnawing the structures and equipment used to protect it. They can gnaw through almost any item softer than steel—wood, lead, soft aluminum, and electrical wires are frequent targets. The resultant damage can increase heating costs, expose grain to moisture, disable electrical equipment, and cause fires. Researchers estimate that up to one-fourth of all fires in the U.S. are caused by the actions of rodents.

Grain Loss by Contamination

Rodent feces and urine poses the greatest threat to stored grain. Norway rats and house mice leave about 20 to 50 droppings per day. These droppings will be strewn along the route taken by rodents traveling from den to feeding sites each night. Urine, unlike droppings, is more difficult to spot, but rats excrete 1/2 oz of urine per night and mice leave hundreds of micro-droplets along trails. While the USDA tolerates one rodent dropping per a 1000-gram sample of corn grain, why take the chance?


Rodents constitute a serious threat to the volume and quality of stored grain. Failure to appreciate the danger can result in significant financial losses. Fortunately, with the right management, the risks can be reduced substantially.

Stephen Vantassel
Extension Wildlife Damage Project Coordinator
Scott Hygnstrom
Extension Vertebrate Pest Specialist