APS Homepage

POSTERS: Chemical control

Residual effect of fungicides applied for flower protection and control of sclerotinia stem rot of soybean
Thomas Jose Justo Miorini - North Dakota State University - Carrington Res Ext Center. Sydney Everhart- Oregon State University, Nicholas Arneson- University of Nebraska-Lincoln, Loren Giesler- University of Nebraska-Lincoln

Boscalid, picoxystrobin, tetraconazole, and thiophanate methyl are fungicides labeled in the US to manage sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum, with application recommended at bloom to prevent flower infection. Since not all flowers open at the time of application, we aimed to characterize residual activity of these fungicides over time. Soybean ‘Williams 82’ was grown under controlled conditions and fungicides were applied at bloom with 187 L ha-1 associated with nonionic surfactant (0.25% v/v), plus the control. Entire plants were collected between 0 and 10 days after fungicide application. Leaves were removed and one to three mature flowers per plant were inoculated with 10µl water with 5,000 ascospores of an isolate of S. sclerotiorum. Plants were incubated in moist chambers at room temperature and disease severity was evaluated daily at 6 to 15 days after inoculation and number of sclerotia counted. AUDPC of disease severity showed all applications reduced disease compared to the control at each day after application. To compare residual activity over time, AUDPC was converted to percent inhibition and analyzed with linear regression. Boscalid and tetraconazole showed evidence of systemicity due to sustained disease suppression over time compared to thiophanate methyl. Sclerotia were reduced after all fungicide applications, although results were inconsistent. Results suggest picoxystrobin reduced formation of sclerotia at 6 days after fungicide application (p<0.10), which may be important for long-term disease management.