White mold can greatly impact soybean yield in Pennsylvania when conditions are favorable for disease development. Credit: Alyssa Collins.
Last year around this time, we saw that most days were cool with lots of morning fog and with excellent conditions for soybean development. Combining these factors, it was not all that surprising that in the end we had white mold impacting production in many areas, especially given the history of the disease in Pennsylvania over the past 20 years.
Taking a look at our 2018 growing season, things are currently rather different, as the soybean growth and development is quite variable, ranging from recently planted soybeans to flowering (R1 to R2 growth stages). Furthermore, we have entered a period of hotter weather around the state with temperatures into the 90’s with a mixed forecast for rain. Nonetheless, it is important to consider the risk that can influence white mold development, especially for those fields that are at or near flowering:
- Disease of high yield potential soybean
- Field history and crop rotation
- Susceptible cultivar
- Row width and plant population (canopy closure and flowering)
- Light intensity (low light at soil surface)
- High soil moisture and high relative humidity
- Duration of leaf wetness > 12 hours
- Cool temperatures (< 85°F)
Integrating these concepts with what we have seen in recent visits to different soybean fields, we noted that soybean stands are not as developed as they were at this time in 2017, nor is canopy closure as advanced or as consistent as occurred last year. We saw pockets of the field where airflow was good given the shorter soybean plants, while in other parts of the field, soybean growth was better developed. For the moment, this may mean that we will not see the exact same conditions we observed last year when white mold was rather severe in many production areas.
One other aspect we are testing to help guide our forecast is a new app that was developed in the Midwest called Sporecaster. The app and the model behind it forecasts the appearance of apothecia as a function weather and soybean row closure for fields grown on 15” and 30” rows, as well as under irrigation or dryland conditions. In fields that we visited in the past few days, the model indicated a moderate risk for white mold in fields that were grown on 15” row spacing and a foliar fungicide would not have been recommended based on the risk. If you are interested in exploring further Sporecaster, it is available for both Android and Apple platforms.
Given the variable soybean growth and development, we will continue to monitor conditions over the next several weeks and provide updates as they are warranted especially given the current crop condition and forecast weather.