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Is "Grape Juice" for the Birds?

Tuesday, April 1, 2003
filed under: Birds

Is BirdShield™ a cost-effective and successful means of repelling blackbirds in sunflower? It depends on who you ask. After two seasons of commercial availability and entering a third, some growers will tell you they’ve had good luck with the “grape juice” product, while others have not. The product’s active ingredient, methyl anthranilate, is a component in Concord and other grapes.

A biodegradable food-grade repellent, BirdShield has been used in all 50 states for fruit, turf, and a variety of crops, including corn and sunflower. Most recently, the product has been registered by EPA for cereal grains, including, sorghum, millet, and oats.

In sunflower, the product is aerially applied to the face of sunflower heads when the crop begins to ripen or birds begin to feed on the crop. Seeds treated with the product are distasteful to blackbirds, prompting them to leave the treated field in search of other food sources. The product's effective life span is about a week, adhering to the treated plant surface until it is broken down by the sun. Hot, sunny weather may shorten treatment effectiveness, while cool, overcast conditions may prolong it.

The product manufacturer’s web site ( states that in sunflower fields treated with two, one pint applications of the repellent at seven day intervals, damage was reduced to about 3% while untreated fields sustained damage from 78% to 90%. These figures represent samples of individually harvested heads from which the damage was both measured and the total amount of seed produced weighed. Harvest weights ranged from 133 to 700 lbs./ac. (mean = 344) in the untreated plots while weights ranged from 1430 to 1909 lbs./ac. in the treated plots.

Company CEO Fred Dunham says people are still learning how to use the new product. “One thing that’s important is that if you anticipate using it, plan ahead and have the product on hand and the aerial applicator lined up. Get it on right before the birds start eating. The guy who waits until he sees birds in the field, then tries to track down a supplier and line up an applicator, there might not be anything left to protect.”

Dunham also stresses that BirdShield is a different mode of action than other bird repellents. “It’s not like a propane cannon, where you get instant results. BirdShield operates over a period of time. You spray it on and you will then see fewer and fewer birds in the treated area over a string of days.”

Some sunflower hybrids have concave heads that droop. This trait on one hand makes it harder for birds to feed. On the other hand, it makes it difficult to treat, so growers may not want to use BirdShield with those types of hybrids, advises Max Dietrich, the NSA’s production coordinator.

Dunham says it has become apparent that water with high concentrates of iron can negatively affect the performance of BirdShield. “There are some areas in central N.D. with such high iron in the wells that I think they’re just going to have to use surface water for application,” he says. A local aerial applicator familiar with conditions most favorable for spraying can also make a big difference in the success of a treatment, he adds.

NDSU Aerial Analysis

Vern Hofman, North Dakota State University extension ag engineer, looked at methods that may improve the efficacy of BirdShield in experiments late last summer.

Spray coverage trials were conducted on the morning of Sept. 6, 2002, near Gwinner, N.D. The spraying was completed with an Ag Cat airplane equipped with core and disc nozzle. Airspeed was about 110 mph, flying height was 8 feet above the crop with an application rate of 5 gallons per acre. To determine coverage, water sensitive paper was used as the catch medium. This paper contains a yellow surface that turns blue when water contacts it.

The water sensitive paper was placed at four positions: 1) on the back of the sunflower head facing up; 2) Face of the head facing down; 3) Stem and leaves about 1/2 way up the plant (hanging vertical to spray); 4) On the ground facing up.

There were three replications of two different spray applications and nozzle arrangements:

1. Nozzles pointing straight back or parallel with the air flow. This

orientation produces large drops.

2. Nozzles turned 90º to the air stream. This causes more wind shear across the

nozzle and smaller drops.

In this experiment, there was not a significant difference in area covered for both nozzle orientations, although head face coverage was somewhat better with a smaller drop. This is explained by the smaller drop being caught in air turbulence caused by the aircraft and wind, with more spray being deposited on the sunflower face. The sunflower heads were mainly facing down and difficult to cover uniformly.

The larger drops do not move vertically as easily with air turbulence, and explains why there’d be less coverage on the heads with larger droplets. Higher droplet values for cards on the ground indicated that larger drops penetrate plant canopies better than small drops. In this case, this is not desirable, as more spray is being lost to the ground with large drops.

A caveat with smaller drops is the increased potential for spray drift, says Hofman. Thus, spraying with smaller droplets may need to be done at times when the spray will be carried away from unintended targets.

Water Tests, Applicator Survey

As part of NDSU’s analysis of BirdShield, water samples from 13 different sources were tested for iron, ph, total dissolved solids, hardness, calcium, magnesium, sodium, potassium, carbonates, bicarbonates, chlorides and sulfates. All samples seemed to work satisfactory as a carrier for BirdShield except for one sample high in iron, at 3.65 mg/liter. This level of iron reacted with BirdShield to form a precipitate that plugged screens and nozzles on the applicator. Another sample contained iron with a concentration of 1.72 mg/liter which did not cause a problem.

Ten aerial applicators were also interviewed regarding the successful action of BirdShield to keep blackbirds out of sunflower fields. Most felt the product was successful, as most customers were satisfied with the results.

Some applicators pointed out that once blackbirds become established in a field, they are hard to move, and BirdShield seemed to work well by keeping migratory birds moving, rather than stopping to feed in a field. Some applicators felt that an early application in late August worked well, while others felt that a later application was best.

A wide range of drop sizes were used by the applicators interviewed, and small drops appear to do the best job of depositing more spray on the face of the sunflower head, echoing the results of the NDSU study. Small drops can easily be produced on an aircraft by directing the spray pattern perpendicular to the air stream or on some nozzles, use a high angle of deflection such as 30 or 90 degrees.

Some applicators indicated that after using BirdShield in their airplane, residue remained on the inside of the tank, which could be removed with a cleaning solution in hot water applied with a high pressure washer.

Hofman says the study indicates that BirdShield can be another strategy used to repel blackbirds from sunflower fields, but that the product is likely to be most effective when used in conjunction with other methods, such as:

• Reducing the number of cattails near sunflower fields.

• Using propane exploders.

• Shooting at them with a gun.

• Harassment with aircraft or other means.

Frightening devices need to be employed especially in the early morning and in

late afternoon, when birds are most actively feeding. If using propane boomers, there should generally be at least one exploder for every 10 acres of crop to be protected. Exploders should be elevated on a barrel stand to “shoot” over the crop, and moved around the field every few days. Exploders should be turned off (manually or with automatic timers) at night to save propane and reduce objectionable noise levels. Boomers should be reinforced occasionally with other scare devices because birds lose their fear of frightening devices over time.

More specific analysis of Hofman’s study can be found on the NSA’s web site, On the home page, click on the link “Research and Statistics,” then the research forum database. Hofman’s study can be found under the “bird predation” for 2003.

Wildlife Services Recommendations

The NSA’s survey of sunflower fields last year indicated that, statistically, bird damage was most noticeable in Minnesota, where about 6% of sunflower fields surveyed overall had some bird damage. However, perimeter damage was over 10% in south central, northwest, and west central South Dakota, and northeast North Dakota. Bird damage occurring after fields were surveyed in September would not be reflected in these figures. The NSA field survey indicated about a 3% drop in bird activity in North Dakota compared to the 2001 NSA field survey.

A USDA Wildlife Services survey of the Southern Drift Plains of ND indicated that the blackbird population last year actually declined even more, about 20%, from an estimated 1.5 million in 2001 to 1.245 million in 2002.

George Linz, leader of USDA/APHIS Wildlife Services office in Bismarck, says dry conditions last year enabled efforts to control blackbird habitat. He also points out that sunflower acreage in North Dakota last year was up about 28% or 300,000 acres from 2001. “So you may have had fewer blackbirds distributed over more sunflower acres.”

Linz says his office is preparing an analysis of BirdShield that will be available later this year. “We have been very careful in evaluating this product, because people’s livelihoods can be affected, both growers who use it and the makers of the product. But ultimately the marketplace will be more important in driving this product than our research will ever be.”

With a per-acre cost of $11 to $12 (product and application), some growers are opting to treat portions of a field with BirdShield, rather than an entire field, next to sloughs or areas where bird pressure is highest. Phil Mastrangelo, state Wildlife Services director for North Dakota, says he hears mixed reports about the product. “We really can’t endorse or discourage the use of this product, since we hear mixed results,” he says. “The bottom line might be that if it works for you, great, then use it.”

Linz and Mastrangelo agree with NDSU that the product should be considered as just one more tool to be used in an integrated approach to blackbird management.

Since most economically-severe blackbird damage to agricultural crops occurs in fields within five miles of roosts, the answer may simply be to not plant sunflower near areas where blackbirds will be a problem, including cattail marshes or woodlots.

If you do plant sunflower, it’s suggested that producers leave access trails every 200 to 300 feet in large fields to aid in scaring birds from the center of the field. Blank rows or strips left for placement of bee hives can be used for this purpose. Planting should be done at the same time as neighbors, because earlier and later ripening fields risks more damage.

“I’m also a big advocate of clean fields,” says Linz. “There seems to be a correlation between weedier parts of a field and blackbird feeding. It makes sense, since weedy areas offer more cover and more feeding opportunities, as do fields where insect populations aren’t controlled.” – Tracy Sayler

Bird Control Products Online

Some companies now offer a new generation of electronic sound devices using digital technology to produce distress calls of specific birds. They are only effective against bird species whose distress calls are encoded on the microchip. Following are some companies on the Internet that market bird harassment products. The National Sunflower Association has not evaluated any of the products and cannot verify the success of their use.

A Year-Round Blackbird Battle Plan


• Once conditions permit, destroy dry cattail areas (tillage, burning, or by other means) which could serve as roosting sites later on. Contact USDA Wildlife Services for spraying larger cattail wetlands. ND: 701-250-4405. SD: 605-224-8692

• At planting, consider north/south orientation if possible that may be less attractive for bird feeding.

• Get a jump on early-season weed control—weedy fields attract blackbirds.

Summer/early fall

• Keep weeds and insects under control, which attract blackbirds.

• Control cattails with herbicides after middle July.

• At bloom, disperse and repel birds that attempt to feed in sunflower fields with products such as boomers, guns, distress call recording, and BirdShield.

• Harvest as early as possible to avoid damage from migrating birds.

• Constantly monitor where blackbirds are roosting and if the wetland is large (10 or more acres) contact USDA Wildlife Services for larger-scale cattail management.

• Evaluate success of disperse and repel methods and products.

Late fall

• With wetland water levels often lower, this can be a good time to cut, burn or disk cattail areas. (Wetlands located on federal or state property or under CRP may require permission from the appropriate agency. That's also the case with such acreage if to be sprayed under the APHIS program.)


• If blackbirds have been a serious problem, try to locate the coming season's sunflower fields away from sloughs and other wetlands, if possible.

• Interested North and South Dakota landowners should contact their state office of USDA-APHIS Wildlife Services for information on enrolling acreage in the coming year's cattail management program, which may include the application of a labeled aquatic herbicide on cattail areas which harbor threatening populations of blackbirds.

• Evaluate blackbird control products and management options.

• If conditions allow, cut or burn cattail areas near future sunflower fields.

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