Date of this Version
Ripening sunflower fields in the northern Great Plains provide blackbirds with easily accessible sources of high-energy food. Blackbirds can be nearly impossible to discourage from foraging in favored fields. Repellents sometimes can be effective feeding deterrents, especially if alternative foraging sites are readily available. Currently, there is one bird repellent (BirdShield®, a.i., methyl anthranilate) registered for use on ripening sunflower. The cost-benefits of BirdShield are being questioned after recent field trails showed no reduction in damage levels (Werner et al. 2005).
Both caffeine and garlic are potential taste repellents that have some promise of reducing blackbird damage to field crops. Avery et al. (2005) conducted cage feeding trials with red-winged blackbirds (RWBL) and brown-headed cowbirds and found that caffeine used at a rate of 2,500 ppm on rice seed significantly reduced food consumption. Trials with mixed species blackbird flocks in a flight pen and field trials in Louisiana showed that caffeine reduced blackbird feeding to <10%. The authors suggested, however, that changes in the formulation were needed to facilitate agricultural spray applications. Mason and Linz (1997) and Hile et al. (2004) showed that garlic-treated food consistently repels European starlings under laboratory conditions. Field trials are still needed to test garlic on ripening grain.
In 2005, we tested the repellent properties of garlic oil and caffeine on caged RWBL. We found that sunflower achenes treated with 4% and 12% w/w garlic oil reduced feeding by 58% and 97%, respectively, compared to untreated achenes. Buoyed by these results, we further explored garlic oil in a second series of experiments at reduced concentrations. Treatments of 2%, 1%, and 0.5% w/w garlic oil reduced feeding by 80%, 40%, and 22%, respectively. In the experiments with caffeine, we found that feeding was reduced by 17% at 0.25% w/w. No other tests were done with caffeine in 2005.
In the cage trials conducted in 2005, we used achenes that were fully coated with repellent. Our current report explores the repellency effects of caffeine and garlic oil when they are sprayed only on the exposed tips of the achenes on intact sunflower heads. Additionally, we report the results of applying liquids to sunflower heads with a helicopter.