Reviewed October 1993
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Blackbirds -- red-winged, grackles and cowbirds -- damage crops. Starlings often mix in these feeding flocks. These birds feed extensively on insects and waste grain during most seasons, although studies confirm that they cause serious damage to ripening fruits, corn and other grains. By July most blackbirds have completed nesting and form large aggregate flocks.
Blackbird flocks make daily flights from their roosts to farms, woods and grasslands. At dawn the birds depart in different lines of flight. They may feed 20 or more miles from their roost. Red-winged blackbirds usually break into smaller groups, while grackles tend to stay in large flocks throughout the day.
Blackbirds damage corn in August when the kernels enter the milk stage. Red-winged blackbirds and grackles tear open the husk and feed on the kernels. The open husk exposes the kernels to further loss from disease.
Damage to fruits, vegetables, small grains and corn may be reduced or avoided by several methods -- modified crop culture; changing bird behavior by frightening the flocks; trapping when bird numbers are limited; excluding the birds from susceptible crops; and using pesticides. Usually a combination of methods is superior to a single method.
Cultural control methods
Planting should be coordinated so that most of the susceptible crops in an area enter the vulnerable stage at the same time. Bird damage is greatest in fields near roosts, near nesting cover, or on flight lines. Consider removing roost cover if a summer roost is on your property. Corn varieties with tight husks resist bird damage and may alleviate the bird-caused loss.
Frightening devices
Gas exploders, shellcrackers, firecrackers, shotguns, recorded blackbird alarm calls, and electronic sound devices may scarce blackbirds from fields. This does not necessarily chase the birds to a nearby crop; they may shift to natural food when it is available.
Scare devices should be activated when the crop first becomes susceptible or when blackbirds first begin feeding on the crop. Devices should be used throughout the day but especially during early morning and late afternoon feeding periods. Several types of scare devices are better than a single device, and their location should be changed frequently.
Gas exploders are the most commonly used scare devices. Effective range varies with locale, but usually one exploder covers about 10 acres. For best results, exploders should be mounted above the height of the crop.
Shotguns using regular ammunition or shellcrackers are effective. The shellcrackers discharge a projectile that explodes in the air some distance from the gun. Use caution with shellcrackers in dry vegetation because of fire hazard. Shellcrackers are available in 12-gauge only.
Frightening devices cause noise that may be objectionable to nearby residents. Check with neighbors before investing in equipment that may be a disturbance to other people.
Trapping
When limited numbers of blackbirds invade orchards or crops other than corn, traps may help. Trap plans can be obtained from Missouri Department of Conservation Wildlife Damage Control Agents.
Excluding blackbirds
When fruits, vegetables, or other crops in limited areas are attacked by birds, durable plastic netting over the crop will effectively keep birds away. This is economically feasible in small areas supporting high-value crops. Plastic netting is particularly useful for home-grounds where low-growing fruit trees, raspberry bushes, strawberries and similar crops can be protected.
Seed treatment
Blackbirds pull sprouting corn and other seeds. Several seed treatment repellents are registered for protection against this damage.
Corn fields
Avitrol Corn Chops-99 is a pesticide registered for protecting standing field and sweet corn against blackbirds. It works on the principle of frightening the flocks by the alarm calls of the few birds that eat the toxic bait. Skilled applicators apply this blackbird pesticide from aircraft, and flights must be well organized with maps, aerial photographs and ground coordination.
Timing the application is critical as it must be applied as corn goes into the milk stage, the time when birds first attack the fields. Crop protection by Avitrol normally requires three applications. Rainfall may create a need for additional treatments. Corn fields must be relatively weed free. Field edges should not be treated. Avitrol is for use by or under the supervision of a licensed pest-control operator. It is not for sale to the general public.
Cherries
Mesurol 75 percent WP is registered as a bird repellent for both sweet and tart cherries. Damage occurs when the cherries begin to color. Cherries are susceptible to damage from robins, finches, blue jays, and cedar waxwings as well as grackles and starlings.
Other fruits
Mesurol 75 percent WP has the potential for preventing bird damage to fruits such as grapes and blueberries. Check with your local MU Extension agent or pesticide dealer on the label registration for grapes and blueberries. Written authorization from the Director of the Missouri Department of Conservation is required to use the above chemicals.
MX138, reviewed October 1993