Effectiveness of Foliar Applications of 9,10-Anthraquinone for Reducing Blackbird Damage to Sunflower

Abstract

Anthraquinone is an effective chemical seed repellent that protects newly planted crops from depredation by granivorous birds. We are experimenting with foliar applications of 9,10-anthraquinone (AQ) to reduce blackbird (Icteridae) damage to ripening sunflower. Sunflower heads generally turn downward as the achenes mature. With the methods currently available for spraying crops, application of AQ directly onto sunflower achenes is nearly impossible. Blackbirds sometimes remove sunflower bracts prior to eating achenes. Thus, getting AQ droplets directly on the achenes may not be necessary, and spraying the heads should expose blackbirds to AQ as they remove bracts. Studies using caged red-winged blackbirds showed that AQ sprayed onto the backs of sunflower heads reduced damage. However, field trials using fixed-wing aerial sprayers and ground sprayers produced inconclusive results. We are currently experimenting with methods to increase spray coverage of AQ while simultaneously attempting to reduce AQ contamination of achenes, thus reducing the likelihood of having to establish food tolerance limits for this comparatively long-lived compound. In this paper, we summarize results from several AQ studies and speculate on when a repellent might be available for sunflower producers.

Inefficiency of anthraquinone‐based avian repellents when applied to sunflower: the importance of crop vegetative and floral characteristics in field applications

“…Previous field efficacy studies involved the application of repellents from above the canopy, assuming the repellent would reach the sunflower face. 19,20 Ideally, residues on disk flowers would reduce feeding while keeping the residue on achenes low enough to conform to US EPA food tolerance levels. 14 In our concentration-response and preference experiments, anthraquinone residue on disk flowers (40-1095 mg kg −1 ) was 183× higher than residue on achenes protected by disk flowers (0-6 mg kg −1 ).…”

“…aerial crop dusters and high-clearance sprayers) results in the product landing on the back of the downward-facing sunflower head, which fails to reduce blackbird feeding as insufficient repellent reaches parts of the plant manipulated by the bird. 16,[18][19][20] Repellent applied directly to the sunflower face has been shown to reduce blackbird damage when applied using a carbon dioxide (CO 2 ) backpack sprayer resulting in extremely high residues on achenes. 16 However, this intense and direct application is not feasible at the scale of commercial sunflower production.…”