Recent estimates by the National Agricultural Statistics Service state that wildlife cause more than $940 million of damage to U.S. agriculture. Rodents are a major contributor to this damage. Zinc phosphide is the most widely used rodenticide to control rodent populations in cropland and rangeland. Unfortunately, zinc phosphide can be hazardous to non-target species, such as birds and fish. In 2008, 67 dead geese were found at Staats Lake in Oregon. Zinc phosphide was detected in 5 of the 6 samples collected. Although the Oregon Department of Agriculture requires below-ground application on zinc phosphide on grasses grown for seed, it is possible that wild geese may consume toxic baits associated with field rodenticide applications.
In studies to reduce non-target hazards to wildlife, NWRC researchers found the addition of an anthraquinone repellent to rodenticide baits successfully prevented the consumption of the baits by captive Canada geese (Branta canadensis)and ring-necked pheasants (Phasianus colchicus). These findings could aid in the development of new bait formulations that reduce ingestion of rodenticides by these and other non-target wildlife species. Anthraquinone, which occurs naturally in some plants, produces a laxative effect when eaten. Anthraquinone is registered as a pesticide by the U.S. Environmental Protection Agency for use as a goose repellent at or near airports, developed urban areas, golf courses, and ornamental and conifer nurseries. Anthraquinone repellents currently are not registered for agricultural applications, although during the 2009 growing season the manufacturer (Arkion® Life Sciences, LLC; New Castle, DE) was issued emergency exemption labels for corn seed treatments in 8 states and rice seed treatments in 3 states.
In addition to having a laxative effect, anthraquinone also absorbs near-ultraviolet light that is visible to most birds. This color cue may facilitate the repellency effect in birds.
“Since anthraquinone exhibits a visual cue and a post-ingestive consequence, anthraquinone is a quintessential avoidance-conditioning agent for wild birds,” notes Dr. Scott Werner, NWRC research wildlife biologist.
In captive studies, researchers treated 2% zinc phosphide baits typically used in rodenticide applications with 2–2.5% anthraquinone. Although some geese and pheasants initially sampled treated baits, all birds subsequently avoided treated baits throughout the remainder of the study. No mortality or signs of zinc phosphide poisoning were observed among 10 geese and 40 pheasants offered the repellent-treated zinc phosphide baits. Additional studies are underway to evaluate the efficacy of the new anthraquinone-zinc phosphide bait for target rodent species. NWRC researchers also plan to investigate possible uses to reduce non-target hazards with other pesticides, compare costs relative to expected damage at unmanaged sites, and assess environmental impacts.
Click here to see related publication “Threshold concentrations of an anthraquinone-based repellent for Canada geese, red-winged blackbirds, and ring-necked pheasants.”
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