Efficiency and profitability of fungicides in controlling Bipolaris diseases and enhancing grain yield in cultivated wild rice (Zizania palustris)

The integrated disease management program for Bipolaris spp. in cultivated wild rice (Zizania palustris) paddies includes the use of one or two fungicide sprays within the growing season, but their effectiveness was questioned due to recent epidemics. To test the efficacy of fungicide applications, on-farm trials were conducted in four Minnesota locations from 2016 to 2018 using five fungicide combinations: QuiltXcel (a.i. propiconazole and azoxystrobin) followed by Quadris (a.i. azoxystrobin) (QX/Q), one early application of QuiltXcel (QX/-), early application of Quadris followed by Quadris (Q/Q), one early Quadris application (Q/-), and one late Quadris application (-/Q). A control treatment without fungicide (-/-) was used. Although there was variation by years and locations, overall, disease severity was reduced and grain yield enhanced in some of the fungicide treated plots compared to the non-treated control. Further, a meta-analysis found that the average disease severity in fungicide treated plants was significantly reduced (p–value = 0.0016) compared to the control. Grain yield of treated plots were also superior to the control (p-value = 0.0061). Grain yield for QX/Q, QX/-, and Q/Q applications were statistically differently from the control with overall grain increases of 200 kg/ha (SEM = 46.7), 123 kg/ha (SEM = 50.2), and 179 kg/ha (SEM = 46.0), respectively. The probability of offsetting fungicide costs for the overall treatments was 85.5% but it differed by treatment from 57% (Q/-) to 87% (QX/Q). Together, these results indicate that the fungicides used within the current disease management program reduce disease and often enhance grain yield in cultivated wild rice paddies.