Wisconsin White Mold Risk Maps – July 4, 2017

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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.

Wisconsin White Mold Risk Maps – June 30, 2017

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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 is currently highest for soybean fields in the west-central to northwest portions of Wisconsin. Risk is further elevated in fields planted to 15″ row-spacing and/or irrigated. While many soybean fields are likely not flowering yet, these risk models should be monitored closely 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 (June 30, 2017)

Apothecial Risk for soybeans planted to 15″ row-spacing, under irrigation

Apothecial Risk for soybeans planted to 30″ row-spacing, under irrigation
This model was 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.

Time to Start Preparing for White Mold Management in Soybean

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

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

Damage from white mold in a soybean field under irrigation.

While many struggled to plant soybeans due to extremely wet weather this season, many fields we have observed are looking quite good. Soybeans planted in early May in the southwest portion of Wisconsin, may be flowering, or approaching the flowering growth stage. The flowering growth stages are a critical time to manage white mold, in-season. You can visit my previous posts dealing with white mold and favorable conditions, or view a fact sheet or video on the subject.

As you probably know, timing in-season fungicide sprays at the correct time during the soybean bloom period can be extremely difficult. To help solve this decision-making issue, a model was 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 apothecia. This model predicts when apothecia will be present in the field using combinations of 30-day averages of maximum temperature, relative humidity, and 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. To view and download a handy user guide for the model, CLICK HERE.

For Wisconsin soybean growers, regular updates and commentary regarding risk of white mold can be found on this blog. Color coded, state-wide maps will be posted and our recommendations will accompany these posts. So be sure to check back regularly or subscribe to the blog to receive an automatic e-mail update when a new post has been added. You can subscribe via the window immediately to the right of this window. The first post for 2017 can be viewed by clicking here. 

If you have decided to spray soybeans for white mold, what are the best products to use? Over the last several years we have run numerous fungicide efficacy trials in Wisconsin and in conjunction with researchers in other states. Fungicides that have performed well in multi-state studies can be found in the 2017 version of the Soybean Fungicide Efficacy Table. In Wisconsin, we have observed that Endura applied at 8 oz at the R1 growth stage performs well. We have also observed that the fungicide Aproach applied at 9 fl oz at R1 and again at R3 also performs comparably to the Endura treatment. Other fungicide options also include Omega and Proline. You can view results of past fungicide evaluations by CLICKING HERE.

For even more detailed information about white mold you can visit the Crop Protection Network page on white mold . You can also find more information about white mold by clicking here and scrolling down to the white mold section.

Scouting for Soybean Seedling Diseases

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

The 2017 planting season has been frustrating for many farmers with frequent rains, wet soils, and cool temperatures. These conditions have resulted in slow, or no planting, for some farmers. To add insult to injury, these conditions are also conducive for many seedling diseases of soybean. The Crop Protection Network, which the UW Field Crops Pathology program is a part of, has generated several useful publications for diagnosing and managing soybean seedling diseases.

The first publication is a full length fact sheet titled “Soybean Seedling Diseases.” This publication can help you differentiate seedling diseases and also herbicide injury, both of which could be issues for many farmers this season.

Speaking of herbicide issues, the CPN has also generated a useful publication on using ILeVO® seed treatment on soybean. Many farmers in Wisconsin have considering using ILeVO® to manage sudden death syndrome and soybean cyst nematode. Farmers should be aware that it is well known that ILeVO® can cause some phytotoxicity to soybean that looks similar to a soybean seedling disease. A useful fact sheet on this phenomenon can be found by clicking here.

Many farmers have elected to use a seed treatment (fungicide, insecticide, nematicide or combination) to protect their seed investment. This is a wise decision, especially considering the cool wet soils that many of us have planted into this season. However, just because a seed treatment was used, there still can be emergence issues. To aid in understanding these issues, the CPN has generated a “Soybean Seed Treatments: Questions that emerge when plants don’t.”

Finally, if conditions remain wet, Phytopthora root and stem rot may affect soybean stands early to mid-season. The CPN has developed a resource which can be found by clicking here. The UW Field Crops Pathology program has also generated a similar fact sheet on Phytopthora root and stem rot that can be found by clicking here.

As always, if you have questions about diseases of soybean, or any field crop, please contact and we can assist in diagnosing and developing a management strategy.

2017 Field Crop Fungicide Efficacy Tables Now Posted

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

Northern Corn Leaf Blight symptoms on a corn leaf.

The 2017 fungicide efficacy tables are now posted for foliar diseases of corn, soybeans, and small grains. New this year is an added efficacy table for fungicides effective against seedling diseases of soybean. You can access these tables by clicking directly on the links imbedded in this page or by clicking on the Fungicide Information tab above, and scrolling down the page to find the tables. The efficacy ratings are generated based on independent, University efficacy trial data from across the U.S. If you can’t find a particular product on the table, it is likely that it isn’t commonly used, or there isn’t enough data to confidently generate an efficacy rating. Remember to follow all label recommendations attached to the fungicide container. The label label is the law!

2016 Wisconsin Field Crops Pathology Fungicide Tests Summary Now Available

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

The 2016 Wisconsin Field Crops Pathology Fungicide Tests Summary is now available online as a downloadable PDF. This report is a concise summary of pesticide related research trials conducted in 2016 under the direction of the Wisconsin Field Crops Pathology program in the Department of Plant Pathology at the University of Wisconsin-Madison.  We thank many summer hourlies and research interns for assisting in conducting these trials.  We would also like to thank Carol Groves, Jaime Willbur, Megan McCaghey, Bryan Jensen, John Gaska, Adam Roth and Shawn Conley for technical support.

Mention of specific products in this publication are for your convenience and do represent an endorsement or criticism.  This by no means is a complete test of all products available.  You are responsible for using pesticides according to the manufacturers current label.  Follow all label instructions when using any pesticide.  Remember the label is the law!

To download the current report, or past reports visit the SUMMARIES page by clicking here.

2016 Wisconsin Pest Management Update Tour Slides Now Live!

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

Yet another Wisconsin Pest Management Update Tour is in the books. It was great to see everyone again this year. I hope you found value in the presentations and that information can improve farm productivity.  As promised, I have uploaded the slides from the 2016 tour with some of our preliminary data from 2016. You can download a PDF by CLICKING HERE. Hope to see you at a winter meeting near you!

Phomopsis seed decay – An Increasing Issue for Delayed Soybean Harvest in Wisconsin

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

Figure 1. Soybean seed affected by Phomopsis seed decay on the left compared to healthy seed on the right.

Figure 1. Soybean seed affected by Phomopsis seed decay on the left compared to healthy seed on the right.

As the rain continues in Wisconsin and the 2016 soybean harvest gets delayed longer, Phomopsis seed decay is going to become an increasing concern. Phomopsis seed decay (Fig. 1) of soybean is caused by the fungus Diaporthe longicolla which is the same fungus that causes pod and stem blight (Fig. 2). This fungus also causes “zone lines” that are often observed in split stems and tap roots. These “zone lines” were once thought to be cause by the charcoal rot fungus, but we now know that is incorrect. You can learn more about “zone lines” by CLICKING HERE.

What does Phomopsis seed decay look like?

The fungus that causes Phomopsis seed decay can infect soybean plants early in the season and colonize pods and infect seeds near, or at maturity. Infected seed will often be shriveled or undersized (Fig 1.) and can have a white or chalky appearance. If pods are opened in the field a white cottony “mold” (different than that of white mold) can be observed. Infected seed can pass the Phomopsis seed decay fungus on in seedlings of the next soybean crop. Therefore, it is important to identify Phomopsis seed decay especially in soybean-seed fields.

Figure 2. Symptoms and signs of soybean pod and stem blight.

Figure 2. Symptoms and signs of soybean pod and stem blight.

What conditions are favorable for Phomopsis seed decay?

Warm and wet weather during pod fill and maturity favor the development of Phompsis seed decay. The conditions were prevalent throughout much of the state in of Wisconsin in 2016. Soybean varieties that matured early are also more prone to Phompsis seed decay. Other stresses such as nutrient deficiencies or virus infections can also increase the occurrence of Phompsis seed decay. Infested seed is a likely source of Phompsis seed decay, however, the fungus can survive on soybean debris and certain weeds like velvetleaf.

How should I handle soybeans with Phomopsis seed decay?

Scout fields before harvest to get an idea of how much Phomopsis seed decay you might have in a field. Scout multiple plants in at least 5 locations in a field, opening pods to determine if Phomopsis seed decay is present. In fields where Phomopsis seed decay is observed, harvest should be prioritized as soon as combines can enter the field. Seed infected with the Phomopsis seed decay fungus will continue to rot in the pod until they are harvested.

How should I manage Phomopsis seed decay in the 2017 soybean crop?

Harvested grain intended to be seed for the 2017 crop should be cleaned thoroughly and undersized or damaged seed removed. Seed with an extremely high incidence of Phomopsis seed decay should not be used. Using a fungicide seed treatment may help improve emergence of infected seed. Resistant soybean varieties should also be used. Choose later maturing varieties appropriate for your location. Earlier maturing varieties tend to be more susceptible to Phomopsis seed decay. Finally, cultural practices such as rotation (corn or wheat are preferred) and tillage to manage infested residue should be considered in high-risk fields.

Additional Resource

A fact sheet about Pod and Stem blight and Phomopsis seed decay has been developed by a consortium of soybean extension pathologists. You can download that fact sheet by clicking here.

 

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

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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

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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 NO. The 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.