Vertebrate Pest Control

Voles, deer, and birds are the three major vertebrate pests of fruit plantings. Voles are mouse-like mammals that eat the bark and roots of young fruit trees and thornless blackberries in winter and are frequently a serious problem. Deer consume the new shoots of fruit trees. Birds damage the fruits of blueberry, cherry, gooseberry, and grape plantings.

Two different vole species cause problems: the meadow vole (which lives aboveground) and the pine vole (which lives belowground). During the spring, summer, and fall, voles eat vegetable matter and seeds. But in the winter they feed on the bark and roots of young trees, often girdling and killing them.

To assess whether or not you might have vole problems before they do damage, place half an apple under a shingle or a i-foot-square piece of plywood in a grassy area near your trees. Check it the next day. If the apple is completely gone, you've got problems that need treating. If there are only a few nibbles, voles are probably present, so you should keep monitoring and consider control measures.

A good way to prevent meadow vole damage is to manage their aboveground habitat. Keep grass cut short so they have no place to hide. Keep weeds and grass cleared out around trees (about 40 percent ground coverage is OK). Don't use straw or fabric mulches, which provide the voles with shelter. But woodchips are OK.

To protect young trees from injury, enclose the base of each trunk with a cylinder of quarter-inch hardware cloth. The cylinder should be about 8 inches in diameter. Bury the bottom shallowly in the soil, being careful not to disturb the roots. The top should be about i8 inches tall and not interfere with

Voles feed on bark and roots of young trees in winter.

the lowest scaffold branch. Mound up pea gravel or mulch a few inches around the cylinder to hold it in place.

Hardware cloth cylinders are less effective with pine voles because you can't install them deep enough to keep out these underground dwellers without damaging tree roots. Because they come aboveground to feed, keeping grass mowed and clear areas around trees helps. But other control measures may be called for.

Repellents or fencing can keep deer at bay, depending on how hungry deer are.

Ripening fruits (especially cherries and berry crops) are frequently damaged by birds. Whether the birds are flocking or nonflocking, migratory or resident, the resulting fruit injury can cause significant losses. The extent of damage varies from year to year and depends on factors such as weather conditions and food supplies.

Which bird species you can expect to damage fruit crops depends on the surrounding environment. Plantings that border forests or brush, for example, attract different bird species than plantings surrounded by open fields or croplands. Plantings located near wooded areas, where birds find shelter and nesting sites, are particularly susceptible to damage. Fruits planted in an isolated area also are vulnerable because the fruit may be the main food source for birds. Some bird species are attracted to plantings near trees or power lines. Planting grass alleyways and controlling weeds within and adjacent to the planting reduces problems with birds. Certain weed species supply food and cover to birds and attract them into the area.

In general, birds feed most heavily early in the morning and again in late afternoon (starlings, which feed throughout the day, are an exception). Adjust your control schedule to coincide with the feeding schedules of the birds.

Several nonlethal methods of bird control are available to home fruit growers. Netting is a traditional and widely used strategy that physically prevents birds from reaching fruit. It is both quiet and effective, but you must apply the netting before the birds discover the ripening fruit (the changes in color as fruit ripens signal the birds to start feeding).

Using poison baits in orchards can pose risks to pets and other wildlife. Box traps, "mouse hotels," and similar control measures are surprisingly effective with voles. Try using apples for bait. Encouraging natural predators such as hawks and owls can also help keep rodent populations under control.

Deer will eat just about anything if they are hungry enough. In areas with heavy deer pressure, the most reliable method to keep them from destroying fruit plantings is to construct an 8-foot-tall fence. Several repellents also can be effective in small home plantings if they are applied and reapplied properly. Hanging a single unwrapped bar of fragrant soap from each tree or bush may discourage feeding if deer pressure is low.

Roll the netting out over the tops of plants and secure it to a support system such as a trellis. The major disadvantages of netting are the high initial cost and the labor involved. Setting up and removing netting on a large scale can be difficult and may require specialized equipment.

Electronically recorded, species-specific distress calls are fairly expensive but effective against certain bird species. The downside is that neighbors may find them as distressing as the birds do. Before purchasing the distress calls, know which species are eating your fruits. Distress calls are most effective when supplemented with some type of visual scare device, such as one of the kite or balloon products bearing the silhouette of a hawk or owl.

Such visual scare devices don't work with all species, however. The hawk kite, for example, scares away starlings, robins, and northern orioles but is not effective with mockingbirds or brown thrashers. Another limitation is local weather. Kites function best in breezy but not windy weather. Furthermore, birds get used to them very quickly and they lose their effectiveness unless supplemented with a noise device.

There are no magic solutions to controlling bird damage. Assess the extent of damage and then determine what species of bird is doing the damage. Netting is probably the most effective but most expensive physical method. Scare devices should be used early to prevent birds from establishing a feeding pattern. A combination of techniques is usually most effective.

For more information, see these Cornell Cooperative Extension publications:

  • Wildlife Damage Management in Fruit Orchards (1994)
  • Managing White-Tailed Deer in Suburban Environments: A Technical Guide (2000)

For ordering information, see: "Related Cornell Cooperative Extension Publications," page 103.

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