Plant growth regulator (Stronghold) enhances repellency of anthraquinone formulation (flight control) to Canada geese

There is a need for nonlethal methods of reducing conflicts between burgeoning populations of resident giant Canada geese (Branta canadensis) and humans at airports and other settings. An anthraquinonebased formulation (Flight Control™ [FC]; 50% anthraquinone [AQ], active ingredient) has shown promise in deterring grazing by Canada geese. We hypothesized that the addition of a plant growth regulator (Stronghold™ [SH]) might enhance the effectiveness of FC by minimizing the exposure of new, untreated grass. To isolate the effects of grass height, plant growth regulator, and the combination of a repellent with a plant growth regulator on grazing by geese, we conducted 3 experiments, each using 24 geese in 6 18.3- × 30.5-m pens in northern Ohio during 1998. We evaluated the response of geese to short (4-11 cm) and tall grass (16-21 cm) in a 9-day test (15-23 Jul). Next, SH (applied at 1.2 L/ha) was evaluated as a grazing repellent in a 14-day test (30 Jul-12 Aug). Finally, we evaluated the effectiveness of FC (2.3 L/ha) combined with SH (0.9 L/ha SH) as a grazing repellent in a 22-day test (11 Sep-2 Oct). We found no difference (P = 0.529) in the number of geese per observation in tall- (1.7 ± 1.5; x̄ ± SE) versus short-grass plots (2.3 ± 1.5), nor in bill contacts per minute (P = 0.777) in tall- (12.6 ± 9.3) versus short-grass plots (11.1 ± 7.9). In the SH test, 14 days postapplication, mean grass height was 12.9 cm in untreated plots and 7.2 cm in treated plots. However, the number of geese per observation on untreated (1.8 ± 1.3) and treated plots (2.2 ± 1.3) did not differ (P = 0.567). Also, there was no difference (P = 0.706) in the number of bill contacts per minute in untreated (15.3 ± 9.9) versus treated plots (18.1 ± 14.2). In contrast, over a 22-day FC/SH test, the mean number of geese per observation was 2.6 times greater (P < 0.001) on untreated (2.9 ± 0.5) versus treated plots (1.1 ± 0.5). Further, the mean number of bill contacts per minute was 8.2 times greater (P < 0.001) on untreated (54.4 ± 11.2) than treated plots (6.6 ± 2.3). We observed no abatement in repellency 22 days posttreatment. Thus, we conclude that SH greatly enhanced the repellency of FC to grazing Canada geese, and we contend that the use of a plant growth regulator with FC will prove effective in reducing goose foraging at airports and other sites.