Sporecaster app validation to improve PA white mold risk prediction.
White mold is a soybean disease that occurs when spores from the fungus Sclerotinia sclerotiorum infect susceptible flowers, leading to growth throughout the soybean plant (Figure 1). Signs of white mold include white, cottony mycelial growth on the stem and black overwintering structures (Figure 2), called sclerotia, form inside the stem and pods. Plants may also display brown wilting symptoms. However, white mold symptoms will only show up after flowering has ended, and treatment options are no longer available.
Figure 2. Sclerotinia sclerotiorum sclerotia found in the soil at the base of the soybean plants. Sclerotia germinate and produce apothecia (small mushroom-like structures) at soybean flowering, which release ascospores that infect soybean flowers. (Photo: Tyler McFeaters, Penn State
Preventative fungicide sprays are the only in-season option for white mold control. Early fungicide application during flowering, between R1 and R3, is critical. When determining whether a fungicide application is warranted, it is important to consider weather as a key factor for risk. The risk of white mold infections increases with cool, wet conditions at soybean flowering. A mobile application developed at the University of Wisconsin-Madison, called “Sporecaster,” helps growers predict the risk of infection and if a fungicide application would be warranted.
Background of the Sporecaster App and validation project:
Validation of the Sporecaster app:
In 2020, we will be monitoring select locations throughout Pennsylvania. We will summarize the risk based on different expected flowering dates, as well as different action thresholds (30% versus 40%). The strength of the Sporecaster app is that we can examine different flowering dates to understand how current weather conditions are influencing the risk model: i.e., is the model trending downward in terms of risk, or is it increasing?
2020 Risk information for the period, July 1 to July 7, 2020
Parameters we use to run the model include:
- 30-inch (this assumes that the 40% canopy closure requirement is met) or 15-inch row spacing
- Flowers Present
- 30% Action Threshold
Table 1. Sporecaster predictions for 2020 in various locations throughout PA. This week’s period is from July 1 to July 7, 2020.
|County||Row Spacing (in)||Risk on 7/1 (%)||Risk on 7/7(%)||Spray recommendation||Week trend||30-Day Avg. Temp(°F)||Avg. Wind Speed (mph)|
Continued validation and white mold scouting during the summer:
To further validate the Sporecaster app, we will scout fields in each of the monitored counties after soybeans reach the R5 growth stage (seed is 1/8 inch long in the pod at one of the four uppermost
Scouting soybeans for white mold is the first step in protecting future crops. An example scouting protocol includes walking a “W” shape through your field. Make 20 stops throughout the field where you can pull back the canopy and get a closer look for white stems and black sclerotia. Where disease severity is high, in the future, you may consider alternative crop rotations to a non-host, wider row spacing in soybeans, or partially resistant varieties.