Field trials will be conducted in 3 locations in south central Michigan. This will be the second year of the two-year study (2017 & 2018). Treatments will include two planting population systems in 15-inch rows. One straight rate populations at 150,000 seeds per acre and the other will be variable rate planting across management zones. The approach for the VRA treatments will be based on the idea of increasing populations in poorer management zones and decreasing populations in highly productive zones. White mold pressure is typically higher in management zones that have high growth rates due to productivity; therefore in these zones plant population would be reduced. Chemical treatments will include the use of a fungicide for control or suppression of white mold and the combination of Cobra herbicide followed by a fungicide. The experiments will be established with a randomized complete block design, with six treatments, and three replications. The plots will be field sized; length of field by 50 to 100 foot wide. The exact size of the individual plots will be determined by the field and equipment size. The beans will be planted in 15" rows. The seeding rates are based on 90% germination soybean seed, if the seed has lower germination, adjustments will be made.

Over the two-year study white mold pressure was relatively low and severity within the plant was also low. Despite those conditions, implementing VRA population and fungicide use was still important. White mold incidence counts were reduced with lower populations, fungicide, and cobra fungicide treatments in both years. The best economic treatment for white mold management in the low pressure seasons was VRA population with a fungicide when averaged across the three locations in 2017 and 2018. On average it increased net dollars $32.86 per acre compared to the standard 150K without fungicide. When averaged across both population treatments the fungicide increased net dollars by $8.50 per acre. However, it was the 2018 response driving the economics; in 2017 it was not economical. There is still some economic risk in managing white mold with Endura fungicide, however on average it still pays. The VRA increased net dollars by $23.68 per acre when averaged across the treatments, excluding the cobra treatments. The VRA population is the best place to start with managing white mold since the economics are strong and there is not much risk. Cobra treatments decreased net dollars on average $87.49 per acre; however the majority of that loss came from Plot #1 in 2018. The use of cobra can reduce white mold pressure; however the risk of not overcoming the burn is too great. Therefore it would not be recommended to use Cobra as a treatment for managing white mold.
The overall objective was to determine if VRA planting should be part of the white mold management recommendation for the state of Michigan. This data would support VRA population as the starting place for managing white mold. White mold pressure is driven by population. The use of a white mold foliar fungicide would also be recommended but the economic response may be more variable based on pressure and late season weather. Overall white mold can be reduced and profitability increased by implementing VRA population and using a foliar fungicide. A systems approach for white mold management is important.