Comparisons between blackbird damage to corn and sunflower in North Dakota

For sunflower producers in North Dakota, blackbird (Icterinae) damage is a chronic problem costing millions of dollars annually. Sunflower damage surveys were last completed in the state in 1979-1980. Since the last surveys, corn plantings have increased 6-fold to 1500 × 103 ha, whereas sunflower hectarage has declined by >75% to 310 × 103 ha. Blackbirds forage on both crops, and this rapid change in North Dakota's agricultural landscape was a sound inducement for reassessing crop damage. Field surveys are an important step in damage methods development because they are used for measuring efficacy, as well as assessing historical changes in the quality and quantity of damage. During 2009-2010, we conducted damage surveys on corn and sunflower. We surveyed 120 randomly selected 3.2 × 3.2-km plots in North Dakota's Prairie Pothole Region. This region of numerous wetlands has historically produced the majority of the state's sunflower crop, in addition to harboring a blackbird population of 25 million birds. Over the 2-year study, we measured damage in 68 cornfields and 27 sunflower fields. Annual damage averaged 5.0 × 103 t (12 kg/ha, US $1.3 million) for corn and 7.2 × 103 t (45 kg/ha, US $3.5 million) for sunflower. Percentage damage was significantly greater in sunflower (x¯=2.7%) than corn (x¯=0.2%). The lower per-unit cost of producing corn makes it a potential lure crop for managing blackbird damage to sunflower. However, the two crops should be phenologically synchronized because corn matures earlier than sunflower and becomes less attractive to blackbirds.