New smartphone app: Sporecaster, The Soybean White Mold Forecaster

Damon Smith, Field Crops Extension Pathologist, University of Wisconsin-Madison

Roger Schmidt, Nutrient and Pest Management Program, University of Wisconsin-Madison

Shawn Conley, Soybean Extension Agronomist, University of Wisconsin-Madison

Sporecaster: A New Soybean White Mold Prediction App for your Smartphone

Sporecaster is a new smartphone application designed to help farmers predict the need for a fungicide application to control white mold in soybean. The app, which is free to use, was developed with support from the Wisconsin Soybean Association and Wisconsin Soybean Marketing Board. It was programmed by personnel in the UW-Madison Nutrient and Pest Management Program.

Sporecaster uses university research to turn a few simple taps on a smartphone screen into an instant forecast of the risk of apothecia being present in a soybean field, which helps growers predict the best timing for white mold treatment during the flowering period.

To learn more about the app, how to download and how to use it, click here.

New Video: Integrated Approaches to White Mold Management

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Have you been struggling with white mold in soybeans over the last couple of field seasons? Do you want to know more about possible approaches to managing white mold in soybean? You might find this new video helpful in your operation. Dr. Damon Smith, UW Field Crops Pathologist, discusses recent data on research of soybean white mold in the North Central U.S. He also provides management recommendations that farmers and practitioners should consider to manage this persistent disease of soybean. For more information on managing white mold you can consult the UW Field Crops Pathology webpage by CLICKING HERE and scrolling down to the white mold section or visit the Crop Protection Network webpage on white mold.

Wisconsin White Mold Risk Maps – August 5, 2017

Jaime Willbur, Graduate Research Assistant, University of Wisconsin-Madison

Sclero-cast: A Soybean White Mold Prediction Model

**This tool is for guidance only and should be used with other sources of information and professional advice when determining risk of white mold development. We encourage you to read the model how-to guide which can be downloaded by clicking here**

Continued dry conditions over the past couple of weeks have helped to continue to decrease white mold risk in non-irrigated fields (Fig. 1). Some areas of high risk still exist in the southern and eastern portions of the state. However, many fields we have visited are moving to R3 and R4 growth stages. Thus, they are getting outside of the extremely critical period for infection by the white mold fungus. Some reports of symptoms of white mold are beginning to come in. I suspect we will begin to see more symptoms of disease over the next couple of weeks and will begin to get an understanding of how severe the epidemic will be this year.

Risk remains high for any soybeans planted to 15-inch rows AND irrigated (Fig. 2). This planting and management scenario is highly conducive for white mold development. We continue to find apothecia under irrigation and in 15-inch row-spacing. I would expect to see significantly higher levels of white mold in irrigated soybeans planted to 15-inch rows. Risk of white mold remained steady for soybeans planted to 30-inch rows and irrigated (Fig. 3). Risk remains high in the southwestern and western portions of Wisconsin for soybeans planted to 30-inch rows and irrigated (Fig. 3).

Forecasts indicate cool temperatures with chances of precipitation for the next week. I would expect white mold risk to hold steady. Continue to growth-stage soybeans and note that map predictions should be considered for making white mold management decisions if soybeans are flowering AND soybean canopies are nearly closed. We have visited fields all over the state and find soybeans well into the reproductive growth stages. We are quickly getting outside the window of opportunity to treat for white mold. Any remaining white mold management decisions should be made very soon. For more information on white mold and white mold management, see this previous post.

Figure 1. Apothecial Risk for non-irrigated soybean fields (August 5, 2017)

Figure 2. Apothecial Risk for soybeans planted to 15″ rows, under irrigation (August 5, 2017)

Figure 3. Apothecial Risk for soybeans planted to 30″ rows, under irrigation (August 5, 2017)

Map Legend: White = model is inactive and risk of apothecia in the field is likely low; Gray = apothecia might be present, but likelihood of apothecial presence is less than 5%; Blue = low risk of apothecia in the field (5 to <15% chance); Yellow = moderate risk of apothecia in the field (15 to <30% chance); Red = high risk of apothecia in the field (30% or higher chance). Model predictions must be combined with soybean growth stage and canopy characteristics to aid in timing of fungicide sprays.


These models were developed at the University of Wisconsin-Madison in conjunction with Michigan State University and Iowa State University to identify at-risk regions which have been experiencing weather favorable for the development of white mold fungus apothecia. Weather information and maps are provided by the Soybean Integrated Pest Information Platform for Extension and Education (iPIPE), which is managed by ZedX, Inc. This model predicts when apothecia will be present in the field using combinations of 30-day averages of maximum temperature, relative humidity, and maximum wind speed. Using virtually available weather data, predictions can be made in most soybean growing regions. Based on these predictions, a map is generated under three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). The maps are colored to show the likelihood of apothecial presence within a region.  If the model is predicting high risk (red) in your area for your planting scenario, the soybeans are flowering, and the canopy is somewhat closed, then the white mold risk is elevated. If your fields are at-risk, we recommend to consult your local extension personnel or resources for the best in-season management options for your area For further information on how to use and interpret these risk maps, CLICK HERE to download a how-to guide.

Wisconsin White Mold Risk Maps – July 27, 2017

Jaime Willbur, Graduate Research Assistant, University of Wisconsin-Madison

Sclero-cast: A Soybean White Mold Prediction Model

**This tool is for guidance only and should be used with other sources of information and professional advice when determining risk of white mold development. We encourage you to read the model how-to guide which can be downloaded by clicking here**

Mostly dry conditions over the past week helped to decrease white mold risk in non-irrigated fields in many locations in the southern and south-central portion of the state (Fig. 1). However, risk remains high in the central area of the state and in portions of the far southern tier of counties.

Risk has increased substantially across the entire state for any soybeans planted to 15-inch rows AND irrigated (Fig. 2). This planting and management scenario is highly conducive for white mold development. We are finding increased numbers of apothecia under irrigation and in 15-inch row-spacing. Risk of white mold also increased slightly in the southwestern and western portions of Wisconsin for soybeans planted to 30-inch rows and irrigated (Fig. 3).

Forecasts indicate seasonable temperatures with little precipitation for the next week. This will give many of us a chance to dry out a bit from above-normal rainfall in July. I expect white mold risk to hold steady or decrease a bit given the forecasts. Continue to growth-stage soybeans and note that map predictions should be considered for making white mold management decisions if soybeans are flowering AND soybean canopies are nearly closed.  For more information on white mold and white mold management, see this previous post.

Figure 1. Apothecial Risk for non-irrigated soybean fields (July 27, 2017)

Figure 2. Apothecial Risk for soybeans planted to 15″ rows, under irrigation (July 27, 2017)

Figure 3. Apothecial Risk for soybeans planted to 30″ rows, under irrigation (July 27, 2017)

Map Legend: White = model is inactive and risk of apothecia in the field is likely low; Gray = apothecia might be present, but likelihood of apothecial presence is less than 5%; Blue = low risk of apothecia in the field (5 to <15% chance); Yellow = moderate risk of apothecia in the field (15 to <30% chance); Red = high risk of apothecia in the field (30% or higher chance). Model predictions must be combined with soybean growth stage and canopy characteristics to aid in timing of fungicide sprays.


These models were developed at the University of Wisconsin-Madison in conjunction with Michigan State University and Iowa State University to identify at-risk regions which have been experiencing weather favorable for the development of white mold fungus apothecia. Weather information and maps are provided by the Soybean Integrated Pest Information Platform for Extension and Education (iPIPE), which is managed by ZedX, Inc. This model predicts when apothecia will be present in the field using combinations of 30-day averages of maximum temperature, relative humidity, and maximum wind speed. Using virtually available weather data, predictions can be made in most soybean growing regions. Based on these predictions, a map is generated under three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). The maps are colored to show the likelihood of apothecial presence within a region.  If the model is predicting high risk (red) in your area for your planting scenario, the soybeans are flowering, and the canopy is somewhat closed, then the white mold risk is elevated. If your fields are at-risk, we recommend to consult your local extension personnel or resources for the best in-season management options for your area For further information on how to use and interpret these risk maps, CLICK HERE to download a how-to guide.

Wisconsin White Mold Risk Maps – July 21, 2017

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Jaime Willbur, Graduate Research Assistant, University of Wisconsin-Madison

Sclero-cast: A Soybean White Mold Prediction Model

**This tool is for guidance only and should be used with other sources of information and professional advice when determining risk of white mold development. We encourage you to read the model how-to guide which can be downloaded by clicking here**

Higher average temperatures this week helped to decrease white mold risk in non-irrigated fields in some locations in the southern and south-central portion of the state (Fig. 1). However, risk remains high in the central area of the state and in portions of the western region.

Areas of high risk have increased in irrigated soybeans planted to 15-inch rows (Fig. 2). Soybeans planted to 15-inch rows and irrigated are under high risk for white mold development in much of the state of Wisconsin. This is consistent with our field observations. Our crew has mostly found apothecia (the small, cup-shaped mushroom) in fields that are irrigated and planted to the 15″ row-spacing. Risk of white mold increased slightly in several pockets along the Wisconsin River Valley and in Jackson and Trempealeau Counties for soybeans planted to 30-inch rows and irrigated (Fig. 3).

Forecasts indicate cooler weather next week. This may increase risk further in some areas, depending on where dew and rain events occur. Continue to growth-stage soybeans and note that map predictions should be considered for making white mold management decisions if soybeans are flowering AND soybean canopies are nearly closed.  For more information on white mold and white mold management, see this previous post.

Figure 1. Apothecial Risk for non-irrigated soybean fields (July 21, 2017)

Figure 2. Apothecial Risk for soybeans planted to 15″ rows, under irrigation (July 21, 2017)

Figure 3. Apothecial Risk for soybeans planted to 30″ rows, under irrigation (July 21, 2017)

Map Legend: White = model is inactive and risk of apothecia in the field is likely low; Gray = apothecia might be present, but likelihood of apothecial presence is less than 5%; Blue = low risk of apothecia in the field (5 to <15% chance); Yellow = moderate risk of apothecia in the field (15 to <30% chance); Red = high risk of apothecia in the field (30% or higher chance). Model predictions must be combined with soybean growth stage and canopy characteristics to aid in timing of fungicide sprays.


These models were developed at the University of Wisconsin-Madison in conjunction with Michigan State University and Iowa State University to identify at-risk regions which have been experiencing weather favorable for the development of white mold fungus apothecia. Weather information and maps are provided by the Soybean Integrated Pest Information Platform for Extension and Education (iPIPE), which is managed by ZedX, Inc. This model predicts when apothecia will be present in the field using combinations of 30-day averages of maximum temperature, relative humidity, and maximum wind speed. Using virtually available weather data, predictions can be made in most soybean growing regions. Based on these predictions, a map is generated under three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). The maps are colored to show the likelihood of apothecial presence within a region.  If the model is predicting high risk (red) in your area for your planting scenario, the soybeans are flowering, and the canopy is somewhat closed, then the white mold risk is elevated. If your fields are at-risk, we recommend to consult your local extension personnel or resources for the best in-season management options for your area For further information on how to use and interpret these risk maps, CLICK HERE to download a how-to guide.

Wisconsin White Mold Risk Maps – July 17, 2017

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Jaime Willbur, Graduate Research Assistant, University of Wisconsin-Madison

Sclero-cast: A Soybean White Mold Prediction Model

**This tool is for guidance only and should be used with other sources of information and professional advice when determining risk of white mold development. We encourage you to read the model how-to guide which can be downloaded by clicking here**

Risk of apothecial presence and subsequent white mold development has increased over the past week in non-irrigated fields (Fig. 1). Cool temperatures and high moisture have increased risk to high levels especially along the southern tier of counties, and into Dodge and Fond du Lac counties. Risk remains high in west-central to northwest portions of Wisconsin and in a band stretching from south-central Wisconsin to northeast Wisconsin.

Areas of high risk have remained steady in irrigated soybeans planted to 15-inch rows (Fig. 2) and 30-inch rows (Fig. 3). Soybeans planted to 15-inch rows and irrigated are under high risk for white mold development in the southern region west-central region and in a band stretching from central to northeast Wisconsin. Risk in irrigated soybeans planted to 30-inch row spacing remains low to moderate.

The Field Crops Pathology crew has also started scouting commercial fields, and research plots, for apothecia. Consistent with the models, we have found apothecia under irrigation on the central sands. We did not find apothecia in dryland environments in the southern tier of the state, where there was low-to-moderate risk expected.

I expect risk to continue to remain steady over the next week, as heat will be accompanied by frequent rain events. Continue to growth-stage soybeans and note that map predictions should be considered for making white mold management decisions if soybeans are flowering AND soybean canopies are nearly closed.  For more information on white mold and white mold management, see this previous post.

Figure 1. Apothecial Risk for non-irrigated soybean fields (July 17, 2017)

Figure 2. Apothecial Risk for soybeans planted to 15″ rows, under irrigation (July 17, 2017)

Figure 3. Apothecial Risk for soybeans planted to 30″ rows, under irrigation (July 17, 2017)

Map Legend: White = model is inactive and risk of apothecia in the field is likely low; Gray = apothecia might be present, but likelihood of apothecial presence is less than 5%; Blue = low risk of apothecia in the field (5 to <15% chance); Yellow = moderate risk of apothecia in the field (15 to <30% chance); Red = high risk of apothecia in the field (30% or higher chance). Model predictions must be combined with soybean growth stage and canopy characteristics to aid in timing of fungicide sprays.


These models were developed at the University of Wisconsin-Madison in conjunction with Michigan State University and Iowa State University to identify at-risk regions which have been experiencing weather favorable for the development of white mold fungus apothecia. Weather information and maps are provided by the Soybean Integrated Pest Information Platform for Extension and Education (iPIPE), which is managed by ZedX, Inc. This model predicts when apothecia will be present in the field using combinations of 30-day averages of maximum temperature, relative humidity, and maximum wind speed. Using virtually available weather data, predictions can be made in most soybean growing regions. Based on these predictions, a map is generated under three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). The maps are colored to show the likelihood of apothecial presence within a region.  If the model is predicting high risk (red) in your area for your planting scenario, the soybeans are flowering, and the canopy is somewhat closed, then the white mold risk is elevated. If your fields are at-risk, we recommend to consult your local extension personnel or resources for the best in-season management options for your area For further information on how to use and interpret these risk maps, CLICK HERE to download a how-to guide.

Wisconsin White Mold Risk Maps – July 11, 2017

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Jaime Willbur, Graduate Research Assistant, University of Wisconsin-Madison

Sclero-cast: A Soybean White Mold Prediction Model

**This tool is for guidance only and should be used with other sources of information and professional advice when determining risk of white mold development. We encourage you to read the model how-to guide which can be downloaded by clicking here**

Risk of apothecial presence and subsequent white mold development has remained steady since last week in non-irrigated fields (Fig. 1). Higher temperatures have offset higher moisture in these drylands situations to keep risk steady. Risk is highest for soybean fields in the west-central to northwest portions of Wisconsin. Risk is also high in a band stretching from south-central Wisconsin to northeast Wisconsin.

The greatest change in risk across the state is in soybeans under irrigation. A significant increase in areas of high risk is predicted in irrigated soybeans planted to 15-inch rows (Fig. 2). Many soybeans planted in this environment are highly likely to see white mold later in the season, if rows are currently closed and soybeans are blooming. Risk has also increased for soybeans under irrigation and planted in 30-inch rows (Fig. 3). Pockets of high risk exist in Jackson, Trempealeau, and Crawford counties if under irrigation and planted to 30-inch rows.

I expect risk to continue to remain high, or increase in some areas, if humidity remains high and timely rains fall. Continue to growth stage soybeans and note that map predictions should be considered for making white mold management decisions if soybeans are flowering and soybean canopies are nearly closed.  For more information on white mold and white mold management, see this previous post.

Figure 1. Apothecial Risk for non-irrigated soybean fields (July 11, 2017)

Figure 2. Apothecial Risk for soybeans planted to 15″ rows, under irrigation (July 11, 2017)

Figure 3. Apothecial Risk for soybeans planted to 30″ rows, under irrigation (July 11, 2017)

These models were developed at the University of Wisconsin-Madison in conjunction with Michigan State University and Iowa State University to identify at-risk regions which have been experiencing weather favorable for the development of white mold fungus apothecia. Weather information and maps are provided by the Soybean Integrated Pest Information Platform for Extension and Education (iPIPE), which is managed by ZedX, Inc. This model predicts when apothecia will be present in the field using combinations of 30-day averages of maximum temperature, relative humidity, and maximum wind speed. Using virtually available weather data, predictions can be made in most soybean growing regions. Based on these predictions, a map is generated under three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). The maps are colored to show the likelihood of apothecial presence within a region. White areas indicate the model is inactive and risk of apothecia in the field is likely low. Gray areas indicate that apothecia might be present, but likelihood of apothecial presence is less than 5%. Blue indicates a low risk (5 to <15% chance), yellow a moderate risk (15 to <30% chance), and red areas indicate a high risk (30% or higher chance). Model predictions must be combined with soybean growth stage and canopy characteristics to aid in timing of fungicide sprays. If the model is predicting high risk (red) in your area for your planting scenario, the soybeans are flowering, and the canopy is somewhat closed, then the white mold risk is elevated. If your fields are at-risk, we recommend to consult your local extension personnel or resources for the best in-season management options for your area For further information on how to use and interpret these risk maps, CLICK HERE to download a how-to guide.

Wisconsin White Mold Risk Maps – July 4, 2017

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Jaime Willbur, Graduate Research Assistant, University of Wisconsin-Madison

Sclero-cast: A Soybean White Mold Prediction Model

**This tool is for guidance only and should be used with other sources of information and professional advice when determining risk of white mold development. We encourage you to read the model how-to guide which can be downloaded by clicking here**

Risk of apothecial presence and subsequent white mold development has increased very slightly since the last posting. Currently, risk is highest for soybean fields in the west-central to northwest portions of Wisconsin. Risk is also high in a band stretching from south-central Wisconsin to northeast Wisconsin. Risk is further elevated in fields planted to 15″ row-spacing and/or irrigated. Early-planted soybean fields are likely beginning to flowering, these risk models should be monitored frequently to assist in making in-season fungicide application decisions during the soybean bloom period. For more information on white mold and white mold management, see this previous post.

Apothecial Risk for non-irrigated soybean fields (July 4, 2017)

Apothecial Risk for soybeans planted to 15″ row-spacing, under irrigation (July 4, 2017)

Apothecial Risk for soybeans planted to 30″ row-spacing, under irrigation (July 4, 2017)

These models were developed at the University of Wisconsin-Madison in conjunction with Michigan State University and Iowa State University to identify at-risk regions which have been experiencing weather favorable for the development of white mold fungus apothecia. Weather information and maps are provided by the Soybean Integrated Pest Information Platform for Extension and Education (iPIPE), which is managed by ZedX, Inc. This model predicts when apothecia will be present in the field using combinations of 30-day averages of maximum temperature, relative humidity, and maximum wind speed. Using virtually available weather data, predictions can be made in most soybean growing regions. Based on these predictions, a map is generated under three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). The maps are colored to show the likelihood of apothecial presence within a region. White areas indicate the model is inactive and risk of apothecia in the field is likely low. Gray areas indicate that apothecia might be present, but likelihood of apothecial presence is less than 5%. Blue indicates a low risk (5 to <15% chance), yellow a moderate risk (15 to <30% chance), and red areas indicate a high risk (30% or higher chance). Model predictions must be combined with soybean growth stage and canopy characteristics to aid in timing of fungicide sprays. If the model is predicting high risk (red) in your area for your planting scenario, the soybeans are flowering, and the canopy is somewhat closed, then the white mold risk is elevated. If your fields are at-risk, we recommend to consult your local extension personnel or resources for the best in-season management options for your area For further information on how to use and interpret these risk maps, CLICK HERE to download a how-to guide.

Question of the week: What is up with all of this white mold on soybeans?

Damon Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Damage from white mold in a soybean field under irrigation.

Damage from white mold in a soybean field under irrigation.

I have been getting a lot of questions this week about the perceived large amount of white mold in soybeans in Wisconsin. There is more white mold out there than we predicted. However, there is also some confusion out there on how all this white mold got there and how to interpret the amount of white mold as it relates to yield loss. Below is a great question I received today and will try to answer below.

Question

What is up with all this white mold? Here is my interpretation of what is going on, correct me if I’m wrong. White mold infection happens at R1, way back in June, but disease symptoms (flagging plants) show up in late July and August, correct?  While the plant got infected in June, the weather needs to be right for the disease to grow – cool nights, warm days and wet conditions. As we go into August these conditions are more common and the disease appears to be spreading when actually it was already there it just needed the right weather to explode? Also I think we often over estimate the amount of infection, it just looks bad, but infection rates are not as high as we think.  If we lose 2 to 5 bushels for every 10% increase by R7, that means if we have a 10% infection rate, we may lose a very small amount 2 bushel or more, maybe 5  bushels.   Assuming 130,000 plants per acre, that would require 13,000 plants per acre to be infected, correct?.

Answer

I’ll answer the easier part of the question first.

  1. Yes, everyone over-rates severity of white mold.  Because it makes those bleached stems that look horrible, everyone estimates it much higher than it is. I had a person tell me that he had a field that was 60-70% white mold. I asked him, “you mean to tell me there are 6-7 plants out of every ten plants in that field infected?” He stopped a minute and then thought about his answer again. Our field crew has rated about 20 fields around the state, in addition to our research plots. In production fields incidence ranges from 0-30% with most in the 10% range. We make 25 stops in a field. We rate the plants in 1 meter for two rows at that stop. We count all the plants in that one meter to establish the stand number, and then count infected plants. We then take a severity index rating too. I try to encourage people to make random stops and count the stand and then infected plants and not try to visually estimate. As humans, we make everything worse – its habit. So yes, at 10% and a stand of 130,000 plants you would need to have 13,000 plants per acre showing symptoms before you can detect reliable yield loss. Sure, you might have sections and pockets where you will have white mold and high yield loss, while other sections of the field yield really well, offsetting that loss. So you need to look across the whole acre to get a good estimate.
  2. Now for the hard part. The data, ours included, show that you have to have apothecia during bloom for infections.  Yes, some plant-plant touching can spread the pathogen, but our data suggest that this method is infrequent. In 2016, the weather during the major part of bloom was really too warm and our models suggested this. However, here is what I’m thinking happened based on our observations and what we know about the white mold fungus biology. First, we had above average rain. Frequent rains can cool the plant canopy and offset the ambient temperature. This fungus is super sensitive to temperature. More so than moisture. Our lab and other labs have done a lot of work on this and it always comes back to temperature that is most important for the white mold fungus. Also, because we had good growing conditions, rows closed quickly this year, giving us thick canopy even at R1; bloom often started early this year. A lot of our soybean varieties are indeterminate and can have an extended flowering period. This also doesn’t help our case. The longer that bloom lasts or flowers are present, the longer the crop is at risk for white mold.  The weather has continued to be conducive now for apothecia.  We continue to find apothecia right now (Mid-August) in our plots and my student is still trapping white mold fungus spores.  This is unusual, but given that the canopy is thick and the weather is mild, not entirely surprising. If there are blooms out there, these spores are infecting. There is about a 10-14 day incubation period in the field. So fresh infections you are seeing now happened in early August. All of this just depends on when the crop bloomed and how long it bloomed for. So, late-planted soybeans with extended bloom periods probably got hit pretty hard. White mold is definitely heavier north of Arlington, Wisconsin.  So I think having a slightly later planting and bloom period coincided with conducive temperature.

Summary

There is a lot of white mold out there. Be diligent in trying to assess the damage. Don’t just visually estimate incidence. Actually make 10-20 stop per acre and count plants with white mold and also total stand at that stop. Convert the white mold numbers to percentage based on the stand count. The rule of thumb is that for every 10% increase in white mold incidence yield loss with range between 2 and 5 bushels.

 

White Mold Showing Up in Wisconsin

Damon Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Wilting and plant death as a result of Sclerotinia stem rot. Photo Credit: Craig Grau.

Wilting and plant death as a result of Sclerotinia stem rot. Photo Credit: Craig Grau.

The UW Fields Crops Pathology team has begun to scout for white mold symptoms in soybean fields around the state. Generally white mold incidence has been relatively light in fields we have visited in the southern half of the state. Some pockets of higher incidence do exist, but pressure has been generally low.

Incidence in the northern half of the state is higher. We have visited fields as far north as Bloomer, Wisconsin and have observed incidence ranging from 3% to 20% of plants infected. Reports from areas in the northwest and northeast also confirm similar findings. Most of the soybean crop is at the R5 growth stage, with some earlier maturing fields approaching R6. Questions have arisen about spraying fungicide now to reduce the damage caused by white mold and preserve yield. The short answer is NOThe reason is that the primary means of infection by the white mold fungus is through soybean flowers. These infections happened several weeks ago. Therefore, the optimal time to spray would be when flowers were out. A low level of plant-to-plant transmission can occur late in the season in soybeans. However, this rate is low enough, that spraying to prevent it does not produce favorable results.

Figure 1. White mold severity index ratings for soybeans treated with or without fungicide at the R5 growth stage.

Figure 1. White mold severity index ratings for soybeans treated with or without fungicide at the R5 growth stage.

In 2014 we conducted a trial where we applied the fungicide Aproach and Endura to soybeans already showing symptoms of white mold and compared these treatments to a non-treated check. These were plots in a production field. We rated them for severity at the time of application and then again 2 weeks later. We also collected yield data.

Aproach and Endura both have good efficacy on white mold when they are applied at the right time. However when applied late (R5 growth stage), like we did in this trial, we noticed no ability of these products to reduce disease advancement. Figure 1 shows the disease severity index ratings of the two treatments compared to the non-treated check. On the left are the pre-spray ratings and on the right are the post-application ratings. All treatments resulted in basically an equal increase in disease. Figure 2 shows the average yield for each treatment. You will notice that there is no statistical separation in yield, with only about a 2 bushel difference among treatments. In fact the yield for all treatments was equally low. There was no response out of these fungicides at this late application timing. Had the timing been appropriate (R1 to R3 growth stages) then we might expect a greater than 10 bushel response out of Aproach and Endura.

Figure 2. Yield of white mold-symptomatic soybeans treated with fungicide at the R5 growth stage or not treated.

Figure 2. Yield of white mold-symptomatic soybeans treated with fungicide at the R5 growth stage or not treated.

How much soybean yield might I lose from white mold?

Research has demonstrated that for every 10% increase in the number of plants that are infected with white mold at the R7 growth stage, you can expect between 2 to 5 bushels of yield loss. Thus, the fields I mentioned earlier will likely range from little detectable yield loss (3% incidence) to as high as 10 bushels lost (20% incidence).

What should I do if I see white mold in my soybean field now?

Get out and survey your fields for white mold. It is a good idea to determine how much white mold you have in your fields, so you can make some educated harvest decisions. One way to move white mold from one field to the next is via combines. You could clean your combine between each field, but this can be time consuming. So my determining which fields have no white mold and which fields have the most white mold, you can develop a logical harvest order by beginning your harvest on fields with no white mold and working your way to the heavily infested fields. This will help reduce spread of the white mold fungus to fields that aren’t infested. You can also make some decisions on your rotation plan and future soybean variety choices based on these late season observations.

If you would like to learn more about white mold and management of this disease, CLICK HERE to download a fact sheet from the crop protection network. You can also watch a short video about white mold by CLICKING HERE.