448085.3 Control of Rodent Damage to Nursery and Landscape Plants
448095.3.1 Rodent Control in Field Situations
Two species of voles damage trees and shrubs in New York nurseries. Meadow voles are found throughout the state and inhabit old fields, roadsides, and other areas with sod cover. Pine voles are a problem in the Hudson River Valley, especially in a five-county area (Dutchess, Orange, Putnam, Ulster, and Westchester). Nurseries in these counties may have both species present and could experience damage to trees during severe weather or when other food sources become unavailable.
The contrasting living habits of meadow and pine voles have important implications for their detection and control. Meadow voles usually live on the surface of the ground. Runways 1 to 2 inches wide through the vegetation, often with droppings and plant cuttings 1/4 to 1/2 inch long, are good indications of their presence. Small openings to underground burrows are evidence of pine voles.
Cultural Practices - Although toxic baits offer reliable control and should be used where voles are abundant, cultural practices can reduce or even eliminate the need for rodenticides. Careful mowing, cultivation, and herbicide treatment will lower rodent numbers because voles require green, growing vegetation for survival and breeding. Efforts to reduce the density of ground cover will aid vole control. The meadow vole is especially vulnerable to close mowing of turf areas, and rotary mowers are much more effective than sickle-bar types for removing ground cover and thatch.
The use of an herbicide strip or cultivation beneath the trees and along the tree rows is a cultural practice that can effectively eliminate meadow voles. In addition, wire guards will protect younger trees from meadow voles as well as rabbits; one-quarter-inch wire mesh has proven most satisfactory. Although a close mowing coupled with herbicide treatments or cultivation can provide outstanding meadow vole control, recent evidence indicates these management practices will reduce, but not eliminate, pine voles.
Pesticides - Monitoring nurseries for signs of vole activity enables growers to detect vole population increases. It also allows growers to evaluate the effectiveness of their baiting programs and the need for follow-up treatments. Apple activity indices can provide a reliable measure of rodent numbers and the potential for damage (see Cornell
Information Bulletin 236, Wildlife Damage Management in Fruit Orchards, for additional information.
Voles are notorious for sudden population irruptions every few years, and growers should monitor their nurseries even in years of low vole densities. Negligence may lead to rapid population increases and aggravated damage problems. Young trees (ranging in age from 1 to 15 years) are most susceptible to vole damage.
For nurseries with recurring meadow vole problems, an annual fall baiting program using a zinc phosphide-treated bait is strongly recommended (Table 5.3.1). Pelletized baits are available from commercial sources. Because meadow voles are active above ground and forage more widely than pine voles, broadcast baiting is more effective against meadow voles. Hand-broadcasting, tractor-operated seeding devices, and whirling-disc fertilizer spreaders are satisfactory means of application. Complete coverage of tree rows and adjacent areas is required for reliable control. However, do not apply baits to areas with bare ground, including vegetation-free cultivated strips under trees, because this may increase the chance of feeding and mortality of nontarget song and game birds. Always follow label directions for rates and observe all precautions. Because there is evidence that bait shyness (voles that consume sublethal doses no longer eat the bait) may occur with repeated use of zinc phosphide baits, a single, complete bait coverage of the site during a period of fair weather is desirable. Ideally, this should follow close mowing of sod areas.
The most important consideration in timing a control program is to achieve the greatest vole reduction just before onset of severe winter conditions. Voles that remain alive in the nursery will survive under the protection of snow cover and can inflict considerable tree damage during the winter months.