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

BACKGROUND Blackbirds (Icteridae) cause significant damage to sunflower ( Helianthus annuus L.) prompting the need for effective management tools. Anthraquinone‐based repellents can reduce feeding by > 80% in laboratory settings, but require birds to learn the negative association through repellent ingestion. We evaluated an anthraquinone‐based repellent applied directly to mature sunflower plants for its ability to reduce bird damage. We used captive male red‐winged blackbirds ( Agelaius phoeniceus ) to evaluate efficacy of two anthraquinone‐based formulations in varying concentrations and applied in a manner attainable by sunflower producers. We also assessed field application methods for repellent coverage and anthraquinone residues when using ground‐rigs equipped with drop‐nozzles situated below the crop canopy. RESULTS The repellents failed to reduce feeding and birds did not exhibit a preference between untreated and treated sunflowers at concentrations 2.7× the suggested application rate (i.e. 9.35 L ha −1 of repellent). In the absence of disk flowers, which obstruct repellent from reaching the achenes, the repellents failed to reduce consumption. Anthraquinone concentrations in field applications were considerably less than those in the laboratory experiments and did not reduce bird damage. CONCLUSION Efficacy is difficult to achieve in the field due to application issues where growth patterns and floral components of sunflower limit residues on achenes, thus contact with foraging birds. Although field residues could be improved by increasing anthraquinone concentrations in tank mixtures and decreasing droplet size, repellents optimized for loose achenes are inefficient in reducing avian consumption of sunflower when applied to intact plants in a manner representative of commercial agriculture. © 2020 Society of Chemical Industry