Response of glyphosate-resistant soybean to dicamba spray tank contamination during vegetative and reproductive growth stages

The anticipated availability of dicamba-resistant crops will increase the potential for crop injury to non-dicamba-resistant soybean due to dicamba spray tank contamination. A total of eight field trials were conducted at various locations in Ontario, Canada during 2012-2014 to determine the response of non-dicamba-resistant soybean to dicamba spray tank contamination at 0, 0.75, 1.5, 3, 6, 15, 30, and 60 g a.e. ha(-1) applied postemergence (POST) at the V2-3 (2-3 trifoliate) or R1 (1st flower) stage. At one week after treatment (WAT), dicamba applied at 0.75, 1.5, 3, 6, 15, 30, and 60 g a.e. ha(-1) at V2-3 caused 12, 18, 25, 31, 43, 53, and 66% visible injury in soybean, respectively. Injury increased at 2 and 4 WAT and decreased by 8 WAT with 68% visible injury observed at the highest dose. Dicamba applied at R1 caused 23, 28, 36, 40, 48, 61, and 73% visible injury in soybean at 0.75, 1.5, 3, 6, 15, 30, and 60 g a.e. ha(-1), respectively. The predicted dose of dicamba to reduce soybean seed yield 1, 5, 10, 20 or 50% was 1.1, 5.8, 11.8, 25.2, and > 60 g a.e. ha(-1) when applied at V2-3 and < 0.75, 1.0, 2.0, 4.3, and 11.5 g a.e. ha(-1) when applied at R1, respectively. Results show that dicamba spray tank contamination of as little as 0.75 g a.e. ha(-1) can cause significant crop injury in non-dicamba-resistant soybean when applied during the vegetative or reproductive stages.