One of the most frequent questions asked thus far after cover crop presentations or events is “How do you control voles in cover crops?” To control these pests, we first need to understand their biology to know how to combat them.

Voles or field mice populations can fluctuate due to a mild winters or lack of food and shelter; therefore, you can see an increase or crash in populations every 2 to 5 years.  There are several different species of voles, but the main crop pests are meadow and prairie voles. Their nests can be both above or below ground and their populations may average 15 to 45 voles/acre and up to 600 causing high crop damage.  Voles do not hibernate, so a winter snow can provide insulation and conceal them.

Vole Activity and Diet

• Voles will forage for food in 15 feet to .25-acre patches.
• Burrow holes that run from their nests that are 1 to 2 inches wide and these will be highly visible when scouting for voles.
• Voles are most active 2 to 3 hours after dawn or before sunset.
• Summer activity occurs at night and winter activities take place during the day.
• Voles eat high protein diets with low fiber: (soybean seeds and emerging cotyledons).
• They will also eat high carbohydrate seeds (corn, wheat, oats)
• They like the following cover crops: red clover, alfalfa, hairy vetch, peas, and soybeans.
• They do not favor the following cover crops: canola, barley, radish, turnip, Sorghum Sudan, and cereal rye.

A circular area or patch of damage in a soybean field caused by voles. (Photo by Stephanie Porter)

Scouting Should Start Before You Plant

1. Start scouting your field(s) around a month before you start planting.
2. If you find 4 to 5 vole colonies close to your field, you can expect significant crop injury, which means that they can significantly reduce corn or soybean stands during the first 21 to 28 days after planting.
3. Voles will dig up and eat newly planted seeds, soybean cotyledons and plants until they reach 6 to 10 inches tall.

Cover Crops Tips to Reduce Voles

• When planting cover crops, rotate mixes and do not broadcast cover crop seed, drilling is preferred.
• Select a cover crop mix that contains 50% species that winter kill and are low growing.
• Moving cover crops down 8 to 12 inches will help to reduce shelter, allow higher predation, and reduce seed head formation as a food source.

Promote Natural Predators of Voles

• Natural predators of voles include fox, coyotes, owls, hawks, snakes, kestrels (American falcon), and American Shrew (looks like a mouse with long snout and teeth -major predator).
• The addition of ten-foot-tall perches or fence posts with a 12-inch bar, that is painted a bright color, will promote many birds such as owls, hawks, kestrels) to prey on voles.
• Kestrel bird houses are also helpful because they will stay and feed on voles year-round.
• Dogs, especially terriers are bred to kill mice and rats; however, beware because terriers can be field diggers!

Cultural Practices that Deter Voles

• Kill the cover crop early (30 days before planting) or plant green into a cover crop to eliminate food and shelter early or give voles something else to eat.
• Make sure that corn (> 2 inches) and soybeans (1.75 – 2 inches) are planted deeply to reduce vole seed damage and allow the crops to outgrow vole feeding.
• Mow vegetation in fence rows and near road ditches, streams, woods, or rock piles to reduce vole shelter to reduce vole numbers.
• Spread chaff at harvest or use a rotary hoe to fluff and spread residue (and spear a few voles).
• Crimping cover crops and drilling (more disc blades) eliminate many voles.
• Use seed repellants such as capsaicin (hot peppers), cayenne pepper, Lorsban or Thriam (both stinking insecticides) may reduce vole feeding.
• Baits (Zinc phosphide pellets in furrow) can be expensive, and effectiveness may vary.  (Read more here)

The key is that no practice is more than 60% effective alone, so it is recommended that an integrated approach or a combination of practices is used to control voles.

Sources:  Controlling Voles in Cover Crops:  Controlling Voles in Cover Crops | 2020-04-06 (covercropstrategies.com) or Controlling voles, aka., field mice:  Controlling voles, aka., field mice – Delphos Herald