Open Space Advisory Board Agenda and Packet 2015 12 09

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Close mowing and weed control in grassy borders adjacent to agricultural crops will reduce the habitat for voles and should reduce damage. oats or peanut butter. Set traps in the fall before most damage occurs. Trapping is not practical for controlling voles on large areas. Poison Grain Baits. Rodenticides usually are a short -term solution to damage by voles. Habitat management usually is more successful than rodenticides for eliminating damage in orchards. Two percent zinc phosphide is the only legal grain bait for controlling voles in Colorado. Zinc phosphide baits are available in pellet form (Bell Laboratories' ZP Rodent Bait AG, Chempar's Ridall Zinc) on oats (Bell Laboratories' ZP Rodent Bait AG, USDA/APHIS /ADC Zinc Phosphide on steam -rolled oats) and on corn (Hopkin's Zinc Phosphide Bait). One study indicated that pelleted zinc phosphide baits provide greater control of voles than zinc phosphide placed on oats or corn. Most of these baits are labeled for use in orchards and groves, nurseries, ornamental and non- bearing fruit trees, grapevine yards, and non -crop areas such as lawns, ornamentals, golf courses, and parks. The labeled method of application varies somewhat among manufacturers. However, most of these products are labeled for hand baiting, broadcast baiting, and/or trailbuilder baiting in orchards and groves, nurseries, and ornamental and non- bearing fruit trees. In grapevine yards, these products are labeled for broadcast baiting. The Chempar product also is labeled for hand baiting. In non -crop areas, these products are labeled for hand baiting in conjunction with a prebait. To prebait, scatter 4 or 6 pounds (see label instructions) of untreated oat groats, rolled oats or barley (see label instructions) per acre, two to four days before placing a toxic bait. Prebaiting encourages consistent acceptance of bait. When hand baiting around trees, place 1 teaspoon (4 grams) of bait at two to four locations around each tree in surface trails or at the mouth of holes leading to underground burrow systems. In non - crop areas, hand baiting generally consists of placing 1 teaspoon of bait around each active burrow or runway. The most successful control is achieved when the bait penetrates the grass cover to reach the runways. To broadcast bait, spread 4 to 10 pounds of bait per acre with a cyclone seeder or by hand. Bait also can be spread with a trailbuilder. A trailbuilder usually is pulled by a tractor, creates a burrow in the ground and deposits 1 teaspoon of bait at 4 to 5 feet intervals. Two to 3 pounds of bait per acre usually is recommended. Zinc phosphide baits are limited for use only on voles of the genus Microtus. Some of the zinc phosphide products and /or usages are limited to meadow voles. To minimize hazards to birds, do not apply zinc phosphide bait to bare ground, areas without vegetation, or in piles. Also, do not apply to crops destined for use as food or feed. Zinc phosphide can be applied to orchards and groves only during the dormant season after harvest. The best time of year to use zinc phosphide baits on lawns is during fall before snow cover. Application of bait during spring, after snow melt, usually is ineffective. Unpredictable rain and snowfall will severely limit the lifespan of baits exposed on orchard floors. During wet periods, place baits in jars, metal cans, bait stations, polyvinyl - chloride tubes, or under tar paper, shingles, and split automobile tires. Unfortunately, baits placed under these objects and directly on the ground absorb moisture and generally do not persist more than two weeks. Because zinc phosphide is toxic to animals, store it away from humans and pets. Zinc phosphide can be absorbed in small amounts through human skin. Wear rubber gloves to avoid contact with the chemical and take extra care to avoid breathing zinc phosphide dust. Product labels will contain additional precautions. Gardening areas can be protected from burrowing rodents through exclusion fencing, provided fencing is 1/4 -inch mesh hardware cloth. This barrier should project 18 inches above the ground and 3 to 6 inches below the surface. Having buried hardware cloth in the shape of an "L" with horizontal leg extending away from gardening bed will provide additional protection from proficient burrowing rodents. Fumigants usually do not work for control of voles because their burrows are too shallow and complex. 12 Colorado State University, U.S. Department of Agriculture and Colorado counties cooperating. CSU Extension programs are available to all without discrimination. No endorsement of products mentioned is intended nor is criticism implied of products not mentioned.