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POSTERS: Chemical control

Impact of soybean maturity on the yield response to one versus two fungicide applications targeting white mold
Thomas Jose Justo Miorini - North Dakota State University - Carrington Res Ext Center. Michael Wunsch- North Dakota State University - Carrington Res Ext Center, Billy Kraft- North Dakota State University - Carrington Res Ext Center, Suanne Kallis- North Dakota State University - Carrington Res Ext Center

White mold, caused by the fungal pathogen Sclerotinia sclerotiorum, can be a damaging disease of soybeans when cool, wet weather occurs during bloom, and fungicides are often employed to manage the disease. White mold primarily infects soybeans through senesced blossoms, and the period of maximum susceptibility to white mold is extended in soybean varieties with longer maturity, which have a longer bloom period. To test whether a second fungicide application is more likely to be needed in longer maturity varieties, 0, 1, and 2 applications of 0.39 kg ha-1 Endura WG (boscalid, 70% by weight; BASF Corp.) were evaluated across 38 varieties from 0.05 to 1.0 maturity in Carrington, ND and 25 varieties from 0.1 to 1.3 maturity in Oakes, ND in 2018. Experimental design was a randomized complete block with a split-plot arrangement and fungicide as the sub-factor. Fungicides were applied at late R1 to full R2 growth stage and 10 to 12 days later. In plots receiving no fungicide, white mold severity index averaged 24% in Carrington and 10% in Oakes. Fungicides reduced white mold by an average of 17% with a single application and 56% with two sequential applications, and the yield increase from two fungicide applications (versus one application) was 105, 250, 402, and 516 kg ha-1 for varieties of 0.05-0.09, 0.1-0.3, 0.4-0.6, and 0.7-1.0 maturity in Carrington and 45, 164, 220 and 304 kg ha-1 for varieties of 0.1-0.3, 0.4-0.6, 0.7-0.9 and 1.1-1.3 maturity in Oakes. The results suggest the yield gain conferred by a second fungicide application may increase with soybean maturity.