Anthraquinone-based repellent for horned larks, great-tailed grackles, American crows and the protection of California's specialty crops

Abstract

Specialty crops include fresh and dried fruits, vegetables, tree nuts, and horticultural and nursery crops. California accounts for 28% of the specialty crop acreage in the United States of America, including 72% of U.S. lettuce production (Lactuca sativa L.), 27% of U.S. melon production and 100% of U.S. almond production (Prunus dulcis L.). We conducted controlled feeding experiments to evaluate an anthraquinone-based repellent for horned larks (Eremophila alpestris L.), great-tailed grackles (Quiscalus mexicanus Gmelin) and American crows (Corvus brachyrhynchos Brehm) associated with the depredation of California's lettuce, melon and almond crops, respectively. We observed 38–100% feeding repellency among horned larks offered wheat seeds (Triticum spp. L.) treated with 168–3010 ppm anthraquinone during the concentration-response experiment. Great-tailed grackles exposed to rice seeds (Oryza sativa L.) treated with 2060–35,400 ppm anthraquinone exhibited 90–100% repellency. We observed 80–100% repellency among American crows offered almonds treated with 2980–31,500 ppm anthraquinone. We predicted a threshold concentration of 5200 ppm anthraquinone for American crows offered treated almonds. Our laboratory efficacy data provide a reliable basis for planning future field applications of anthraquinone-based bird repellents for the protection of specialty crops. Supplemental field efficacy studies are necessary for the registration of avian repellents and the management of agricultural depredation caused by wild birds.