Wisconsin Field Crop Disease Update – August 10, 2024

/in , , , , , , /by

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

Tar Spot of Corn

Figure 1. Statewide tar spot risk as calculated by the Field Prophet tool for August 10, 2024.

You can find the most recent updates on tar spot confirmations across the U.S. here: https://corn.ipmpipe.org/tarspot/. The Field Prophet tool is also showing mostly moderate risk across the southern two-thirds of Wisconsin, with just the northern tier with high risk for tar spot development at this point in the season (Fig. 1). This means that the weather is less conducive for tar spot development and spread. We are also quickly approaching the end of the in-season management window for applying fungicides in corn for tar spot control. For the major foliar diseases of corn, including tar spot, the optimal window to apply fungicides and maximize return on investment, is between the VT/R1 and R3 growth stages. If your crop has reached the milk growth stage and you are still not seeing any disease and the Tarspotter risk isn’t high, you can hold off on the fungicide application. The likelihood of a yield-limiting tar spot epidemic is low in this situation. You can learn more about fungicide application for tar spot control here.

White Mold of Soybeans

Figure 2. Statewide white mold risk as calculated by the Field Prophet tool for August 10, 2024.

The risk for white mold according to Field Prophet is a bit higher compared to tar spot. Risk is generally high across the state with several pockets of low or medium risk. This means that weather has been conducive for the development of the mushroom-like structure (apothecia) of the white mold fungus that gives rise to spores that infect soybean. These risk estimates appear to be accurate as we continue to find apothecia in fields with a history of white mold (Figure 3). With that said, the soybean crop is quickly approaching the R4 growth stage or beyond, where the opportunity of infection by the white mold fungus does not exist. Thus, there is not a need to spray for white mold beyond the R4 growth stage. Similar to tar spot, the optimal timing of fungicide application ranges from the R1 growth stage to the R3 growth stage in soybeans. If you no longer see flowers on soybeans, then the risk for infection by the white mold fungus is low, despite conducive weather for the fungus.

Use Predictive Tools like a “Crystal Ball”

We continue to get questions about how the apps (Tarspotter, Sporecaster, and Field Prophet) should be used to make decisions about in-season disease management. We have designed these tools to be predictive. This means that the risk indexes you see are telling you that in the next week or two, you might see these diseases pop up. We developed these tools to act like a “crystal ball” so that you can look ahead and apply fungicides in a preventative manner. We know that fungicides work best when applied preventatively. In addition for diseases like tar spot, the fungus that causes this disease has a very long incubation period (time from infection to when you actually see tar spots). This time period can be as long as 30 days. So a high risk today, might indicate seeing tar spot show up even a month from now. Be sure to use these tools to look into the future and to prepare yourself, rather than being reactionary.

Figure 3. Apothecia of the white mold fungus at the base of a soybean stem.

Other Diseases to Watch

Figure 4: Northern corn leaf blight (NCLB) lesion on a corn leaf.

We are starting to find more and more northern corn leaf blight (NCLB; Figure 4) in some fields in Wisconsin. This makes sense as the weather recently has been cooler and wetter. Luckily most of the fungicides used for tar spot also have good efficacy against NCLB. Thus if you sprayed for tar spot, you have probably controlled NCLB too. For those with silage corn, especially brown mid-rib (BMR) hybrids, continue to scout your fields for NCLB. Some BMR hybrids are very susceptible to this disease. If NCLB begins to move quickly and you are approaching your harvest window, you might consider chopping a bit earlier in order to reduce damage by NCLB.

We also continue to watch the frogeye leaf spot situation in soybeans. Our beta-testing models for frogeye leaf spot have shown relatively low risk for this disease in Wisconsin this season. We also have not found any frogeye leaf spot to date. However, the risk is creeping up in southern Wisconsin. The window to treat for this disease ends around R5. Thus, I believe most of the soybeans in Wisconsin will escape frogeye leaf spot without the need to apply a fungicide this season. However, keep an eye on your fields and continue to scout to stay informed of the situation.

Mid-Season Corn and Soybean Disease Update and New Corn Fungicide ROI Calculator

/in , , , , , , , /by

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

Tar Spot and Corn

Figure 1. Statewide tar spot risk as calculated by the Field Prophet tool for July 22, 2024.

You can find the most recent updates on tar spot confirmations across the U.S. here: https://corn.ipmpipe.org/tarspot/. The Field Prophet tool is also showing mostly moderate to high risk across the state of Wisconsin (Fig. 1). This means that if your crop is between VT/R1 and R3 you should be actively scouting for tar spot and making the decision to apply a fungicide at this time. Our research has shown that one well-timed application of fungicide somewhere between VT/R1 – R3 will control tar spot enough for a yield response even in a heavy-pressure year. You can learn more about managing tar spot BY CLICKING HERE. If you think you found tar spot I would appreciate if you would let us know. We can enter the county level data into the Corn IPMPipe Map and contribute to the cause.

Gray Leaf Spot and Corn

We are also watching the gray leaf spot (GLS) situation closely. The southern and southwestern portions of the state have had enough heat and moisture that risk is likely high for this disease in those locations. For the rest of the state, risk isn’t as high, but likely moderate risk exists. Fortunately, the same fungicides that work well in controlling tar spot, also work well against GLS. Thus, another reason that a fungicide application may need to be considered at this point in the season.

Corn Fungicide ROI Calculator

With the tight margins in the corn market, and a high risk for disease due to wet weather, I have been getting a lot of questions about fungicide return on investment (ROI) this season. Fortunately, the scientists involved in the Crop Protection Network have been working on amassing fungicide performance and ROI data over the last few seasons and have launched a new interactive Fungicide ROI tool. The tool is research-based using data from across the entire U.S. corn production belt, including Wisconsin. During the studies included in this dataset, the diseases of interest were tar spot and also southern rust. Both are again diseases of interest this season. The tool can be used to run various scenarios that fit your farm and situation in the 2024 growing season. You can change the expected end-of-season disease severity levels, and the pricing of products included in the tool. Not all products labeled for corn can be found there, but most of the popular ones are included. You can also adjust the sale price for your crop, and expected farm yield, so that you can get real estimates of ROI and probability of breaking even for your situation. An example scenario can be found in figure 2 where I adjusted the tool to 180 bu/a yield and a corn sale price of $4 per bushel with expected high levels of tar spot or southern rust. You can see that several products result in a positive net benefit per acre using default product pricing. However, the tight margins this year, do result in lower breakeven probabilities. I would suggest running the tool for your situation. Be honest with yourself and put real numbers in the tool. This tool may be helpful for you if you are on the fence about spraying a fungicide this year. If you have a known resistant hybrid, your crop is already through to R3, and no disease has shown up yet, you might be able to help your financial situation by not spraying this season.

White Mold and Soybeans

Figure 3. Statewide white mold risk as calculated by the Field Prophet tool for July 22, 2024.

The risk for white mold according to Field Prophet is a bit spottier compared to tar spot. Mostly the northern and central portions of the state are at high risk with some pockets of moderate risk. The southeastern portion of Wisconsin is at low risk currently (Fig. 3). This is due to hotter temperatures several weeks back. Regardless of location, our models are telling us that the risk for white mold will continue to rise across the state over the next 7 to 10 days. If you are in a low-risk area and you are at R3 or beyond, you might not have much to worry about for this year when it comes to white mold. However, if you are in a moderate-risk zone, watch this situation carefully. If you are at R3 and the crop has good canopy, you might consider one late R3 application. If you are in a high-risk zone, the crop has canopied, and your soybean crop is in the bloom period, it is time to think about a fungicide application. These will be the areas I would expect to find white mold 1-3 weeks from now. If you would like to learn more about white mold management, check out my previous article HERE.

As always, get out and look at the crop. Scout, scout, scout!

It’s that time of year again: What to do about white mold of soybean?

/in , , , /by

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

Shawn Conley, Extension Soybean and Small Grains Agronomist, Department of Plant and Agroecosystem Sciences, University of Wisconsin-Madison

It is time for my annual reminder about white mold in soybeans, and its management. The 2023 season in Wisconsin was all about drought and heat. So far, the 2024 season has been on the opposite end of the spectrum. Don’t be complacent about managing white mold this year.

Figure 1. Apothecia, a small mushroom-like structure of the white mold fungus that give rise to spores, which infect soybean flowers.

Remember that the white mold fungus infects soybeans through open and senescing flowers, by spores that are born from small mushroom-like structures called apothecia (Fig. 1). Remember that if the bloom period gets extended due to cool weather, this can lead to an extended window for infection by the fungus. Often cool weather is a double whammy as it is good for the white mold fungus and slows down soybean crop development, thereby extending bloom. This could be at play this season, stay on top of your game!

Given the moderate temperatures and moisture we have been getting the risk for white mold is currently moderate to high for the central to northern tiers of the state, while the far southern tier is at generally low risk (Fig. 2).

Predicting White Mold 

The flowering growth stages are a critical time to manage white mold in-season. You can view a fact sheet and 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, 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 apothecia. These models predict 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. To facilitate precise predictions and make the model user-friendly, we use the Sporecaster smartphone application for Android and iPhone and also the Field Prophet app for iPhones.

Figure 2. Map of white mold risk generated in the Field Prophet app for Wisconsin, July 8, 2024.

The purpose of the smartphone app is to assist farmers in making early season management decisions for white mold in soybean. The best time to spray fungicides for white mold is during flowering (R1 and R3 growth stages) when apothecia are present on the soil surface. If you have trouble growth-staging soybeans, here is a helpful guide on correctly identifying soybean growth stages.

University research has indicated that the appearance of apothecia can be predicted using weather data and a threshold of percent soybean canopy row closure in a field. Based on these predictions and crop phenology, site-specific risk values are generated for three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). Though not specifically tested we would expect row-spacings of 22 inches or less to have a similar probability response to fungicide as the 15-inch row-spacing.

The Sclerotinia apothecial models that underlie the Sporecaster prediction tool have undergone significant validation in both small test plots and in commercial production fields. In 2017, efficacy trials were conducted at agricultural research stations in Iowa, Michigan, and Wisconsin to identify fungicide application programs and thresholds for model implementation. Additionally, apothecial scouting and disease monitoring were conducted in a total of 60 commercial farmer fields in Michigan, Nebraska, and Wisconsin between 2016 and 2017 to evaluate model accuracy across the growing region. Across all irrigated and non-irrigated locations predictions during the soybean flowering period (R1 to early R4 growth stages) were found to explain end-of-season disease observations with an accuracy of 81.8% using the established probability thresholds now programmed in the app. We have made additional improvements for 2024, to further refine accuracy. So if you have used Sporecaster before, you might want to check the version in the “Help and Info” button to be sure you have version 1.41.3 of Sporecaster.

We also know that for highly susceptible soybean varieties, the action threshold should be adjusted down. Research in the upper Mid-west demonstrated that for most soybean varieties the default action threshold depicted in the tool when you set up a field is accurate. However, some varieties are highly susceptible and the action threshold should be moved down from 40% to 20% for varieties that are known to be highly susceptible. this can improve accuracy of the tool and recommendation for fungicide application.

Not only can users run predictions of risk during the soybean bloom period for any field, but you can also set up visual maps to look at multiple sites simultaneously. An example for the state of Wisconsin can be found in figure 2, which represents risk for July 8, 2024, for non-irrigated soybeans. Currently, if soybeans are flowering, risk is moderate-to-high in much of Wisconsin for non-irrigated soybeans. I personally like the Field Prophet version of the prediction tool a bit better as it provides a 7-day historical trend of risk and also provides a 7-day true forecast. The historical trend lines can be viewed on the fly in your field list (Fig. 3). If the trend is moderate, but the slope of the line is increasing, then you might want to keep a close eye on the white mold risk. We find that the trends are much more informative for decision-making vs. just the daily instantaneous risk level.

Figure 3. 7-day historical white mold risk trend lines as depicted in the Field Prophet app on July 8, 2024.

What to Spray for White Mold?

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. In Wisconsin, we have observed that Endura applied as a single application at 8 oz at the R3 growth stage performs well. The window to spray runs from R1 to R3, but our recent data suggests waiting a bit into that window improves efficacy of the fungicide application vs. spraying at R1. If you do choose to spray at the R3 growth stage, be sure to focus on getting good canopy penetration with your fungicide spray. Soybean canopies at R3 can be dense and hauling more water, slowing your sprayer speed, and increasing spray pressure can all help improve spray penetration in those dense canopies. Other fungicide options also include Omega and Proline. You can view results of past fungicide evaluations for Wisconsin by CLICKING HERE. If you would like to run tailored estimations of return on investment for various fungicide programs, you can use another smartphone application called Sporebuster.

What is Sporebuster?

When a fungicide application is needed to control white mold in soybeans, Sporebuster can help determine a profitable program. You enter your expected soybean price, expected yield, and treatment cost. Sporebuster instantly compares ten different treatment plans at once to determine average net gain and breakeven probability of each. You can mark, save and share by email, the best plans for your farming operation.

The purpose of Sporebuster is to assist soybean farmers in making a fungicide program decision that is profitable for their operation. Sporebuster is meant to complement Sporecaster. Once Sporecaster recommends a fungicide application, Sporebuster can be used to determine a profitable program.

Information that drives Sporebuster is based on research from 2009-2016 from across the upper Midwestern US. Statistical models were developed based on these data that included white mold pressure and yield response from fungicide for 10 common fungicide programs. Due to recent changes in the markets, be sure to manually adjust the cost of the product you are interested in, so that the tool returns an accurate estimate of return on investment. My advice is to call local suppliers and see what products you can get and what the per acre cost will be to get the application done. Details about the research behind Sporebuster can be found by CLICKING HERE.

Helpful Smartphone Application Links

Sporecaster

  1. Click here to download the Android version of Sporecaster.
  2. Click here to download the iPhone version of Sporecaster.
  3. Click here to download the Field Prophet version of Sporecaster for the iPhone.

Sporebuster

  1. Click here to download the Android version of Sporebuster.
  2. Click here to download the iPhone version of Sporebuster.
  3. Here is a video on how to use Sporebuster and interpret the output.

Other Resources

  1. To watch an in-depth video on white mold management, CLICK HERE.
  2. To find more information on white mold, view a web book from the Crop Protection Network, CLICK HERE.

Scientific References

  1. Willbur, J.F., Fall, M.L., Blackwell, T., Bloomingdale, C.A., Byrne, A.M., Chapman, S.A., Holtz, D., Isard, S.A., Magarey, R.D., McCaghey, M., Mueller, B.D., Russo, J.M., Schlegel, J., Young, M., Chilvers, M.I., Mueller, D.S., and Smith, D.L. Weather-based models for assessing the risk of Sclerotinia sclerotiorum apothecial presence in soybean (Glycine max) fields. Plant Disease. https://doi.org/10.1094/PDIS-04-17-0504-RE
  2. Willbur, J.F., Fall, M.L., Byrne, A.M., Chapman, S.A., McCaghey, M.M., Mueller, B.D., Schmidt, R., Chilvers, M.I., Mueller, D.S., Kabbage, M., Giesler, L.J., Conley, S.P., and Smith, D.L. Validating Sclerotinia sclerotiorum apothecial models to predict Sclerotinia stem rot in soybean (Glycine max) fields. Plant Disease. https://doi.org/10.1094/PDIS-02-18-0245-RE.
  3. Fall, M., Willbur, J., Smith, D.L., Byrne, A., and Chilvers, M. 2018. Spatiotemporal distribution pattern of Sclerotinia sclerotiorum apothecia is modulated by canopy closure and soil temperature in an irrigated soybean field. Phytopathology. https://doi.org/10.1094/PDIS-11-17-1821-RE.
  4. Willbur, J.F., Mitchell, P.D., Fall, M.L., Byrne, A.M., Chapman, S.A., Floyd, C.M., Bradley, C.A., Ames, K.A., Chilvers, M.I., Kleczewski, N.M., Malvick, D.K., Mueller, B.D., Mueller, D.S., Kabbage, M., Conley, S.P., and Smith, D.L. 2019. Meta-analytic and economic approaches for evaluation of pesticide impact on Sclerotinia stem rot control and soybean yield in the North Central U.S. Phytopathology. https://doi.org/10.1094/PHYTO-08-18-0289-R.
  5. Webster, R.W., Mueller, B., Conley, S.P., and Smith, D.L. 2023. Integration of soybean (Glycine max) resistance levels to Sclerotinia stem rot into predictive Sclerotinia sclerotiorum apothecial models. Plant Disease. https://doi.org/10.1094/PDIS-12-22-2875-RE.

2023 Wisconsin Fungicide Test and Disease Management Summary Now Available!

/in , , , , , , /by

Brian Mueller, Researcher II, UW-Madison, Plant Pathology

Damon Smith, Professor and Extension Specialist, UW-Madison, Plant Pathology

Each year the Wisconsin Field Crops Pathology Program conducts a wide array of fungicide and disease management tests on alfalfa, corn, soybeans, and wheat. These tests help inform researchers, practitioners, and farmers about the efficacy of certain fungicide products on specific diseases and how to pair them with other disease management strategies. We hope you find this report useful in making decisions for the 2024 field season.

The 2023 Wisconsin Field Crops Fungicide Test and Disease Management Summary is available by clicking here. These tests are by no means an exhaustive evaluation of all products available, but can be used to understand the general performance of a particular fungicide in a particular environment. Keep in mind that the best data to make an informed decision, come from multiple years and environments. To find fungicide performance data from Wisconsin in other years, visit the Wisconsin Fungicide Test Summaries page. You can also consult publication A3646 – Pest Management in Wisconsin Field Crops to find information on products labeled for specific crops and efficacy ratings for particular products. Additional efficacy ratings for some fungicide products for corn foliar fungicides, soybean foliar and seed-applied fungicides, and wheat foliar fungicides can be found on the Crop Protection Network website.

Mention of specific products in these publications are for your convenience and do not represent an endorsement or criticism. Remember that this is by no means a complete test of all products available.  You are responsible for using pesticides according to the manufacturers current label. Some products listed in the reports referenced above may not actually have an approved Wisconsin pesticide label. Be sure to check with your local extension office or agricultural chemical supplier to be sure the product you would like to use has an approved label.  Follow all label instructions when using any pesticide. Remember the label is the law!

Wisconsin Field Crops Disease Update, August 9, 2023

/in , , , , /by

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

Figure 1. A Screen shot of a map developed in the Field Prophet app showing risk for tar spot development in Wisconsin as of August 9, 2023.

Well, it was going to happen sometime soon, tar spot has been confirmed in two counties in Wisconsin. You can track tar spot confirmations in realtime HERE. Both Lafayette and Rock counties were confirmed to have low levels of tar spot in several fields this week. The good news is that these finds are a month behind the initial confirmations in the state for the last two seasons. What does this mean? Well, it means that the tar spot impact on grain yield will likely not be has significant as it has been over the last couple of seasons. Exceptions to this statement will include late-planted corn where the current growth stages are around VT (tasseling) and susceptible silage hybrids. You should scout and track these situations carefully. Be prepared to chop silage early if tar spot really starts to move. You will want to watch moisture carefully in these situations.

The current risk for tar spot development remains moderate to high across much of the state (Fig. 1). Cooler weather and dewy evenings and mornings are keeping the risk elevated. Fungicide applications for much of the corn in the state should have happened already. Remember the optimal time to apply fungicides to control tar spot (and most other foliar corn diseases) is between the VT (tasseling) and R3 (milk) growth stages. Spraying fungicide after R3 has not yielded much of a return on investment. If you find tar spot, please don’t hesitate to send a high-quality photo to damon.smith@wisc.edu. We don’t disclose exact locations, but do like to track the county-level tar spot information. If you would like to learn more about tar spot and managing it, see my previous post HERE.

Figure 2. Sporecaster predictions for selected non-irrigated locations in Wisconsin for August 9, 2023.

In other news, white mold risk ranges from low in the southern portion of the state to moderate and high in the mid and upper portions of the state, respectively (Fig. 2). Most soybeans are probably headed toward the R4 or R5 growth stage. This means fungicide applications will no longer yield positive returns on investment. If soybeans were planted late and they are still in the R1 to R3 growth stages and you are in a moderate to high risk area, a fungicide should be applied at this time. If you would like to learn more about white mold management, see my previous post HERE. We have observed active white mold on susceptible varieties under irrigation already this season. I am anticipating pockets of white mold in the state, especially in our typical areas of concern in the central and northeastern quadrants.

As always, make sure you are out and scouting to be prepared for what is coming ahead!

Wisconsin Field Crops Disease Update, July 27, 2023

/in , , , , , , , /by

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

Shawn Conley, Extension Soybean and Small Grains Agronomist, Department of Plant and Agroecosystem Sciences, University of Wisconsin-Madison

Rains continue to fall around Wisconsin. While we still have a moderate drought in much of the state, some of that drought is being alleviated. However, with these timely rains, come disease concerns. Here are our thoughts on what is happening.

Phytophthora Root and Stem Rot of Soybean

Figure 1. Stem rot symptoms of Phythophthora rot and stem rot on soybeans.

It has been a couple of years since we have seen a significant epidemic of Phytophthora root and stem rot (PRSR) of soybean. However, since it has started raining, we have got a good look at how susceptible many of our soybean varieties are here in Wisconsin. PRSR is primarily cause by the fungal-like organism, Phytophthora sojae. PRSR is usually worse in fields that are no-till and/or are slow to drain. The PRSR pathogen likes to survive in old soybean residue and can also persist as a long-term survival structure in the soil itself. The organisms that causes PRSR becomes active if the soil temperatures are over 60 F and the soil becomes saturated. We had those conditions occur back in early to mid-July. Once the soil dried out a bit and a bit of environmental stress kicked in, we can readily observe the damage the organism caused in early July. Primarily what we are seeing right now is the stem rot phase (Fig. 1), with the symptoms including wilting of the plant and a distinct purple-brown lesion extending from the soil surface upward. If plants are pulled from the ground, you will also see poor root systems which is where the organisms typically first infects and causes damage.

At this point in the season, there is nothing that can be done.  DO NOT spray foliar fungicides for this problem. This will not be effective. You will want to check on the variety with the symptoms and consult the tech sheet to see what type of “Phytophthora gene” may have been included in the variety. These genes are called Rps genes and provide race-level resistance. The population of the PRSR pathogen can be a single race or mixed races in the field. The last time a survey of Phytophthora races was done in Wisconsin, it was noted that the Rps 1-k resistance gene should be effective on about 99% of the acres in the state. However, that survey was done over 15 years ago. Due to heavy use of the Rps 1-k resistance gene, we believe that the population in the state has shifted. We are seeing that resistance readily overcome. Unfortunately, most of the varieties currently grown in the state have this resistance. A recent check of the soybean variety trials 2022 show that out of 265 varieties tested 25% had no PRSR resistance gene, 2% had Rps 1-a, 29% Rps 1-c, 26% Rps 1-k, 9% Rps 3-a, and 9% had multi-genes. We are actively working with the Wisconsin Soybean Marketing Board to understand what the current population looks like. However, it is too early to tell what the races are primarily in our fields. Moving forward. perhaps choosing Rps 3-a or mixed gene varieties could help, but that is a shot in the dark for now.

Other things you can do for PRSR are to open up the rotation between soybean crops, and improve drainage in fields that are typically saturated for long periods of time. Like I said above, adjusting variety choice can help too. Seed treatment fungicides can also be used. However remember that the seed treatment is only going to be effective for the first 30 days or so after planting. After that we have to rely on varietal resistance to manage this problem. If you would like to find efficacy data on the seed treatments you can find that HERE.

We are looking for samples of PRSR from around Wisconsin. So feel free to reach out (damon.smith@wisc.edu) and we can coordinate getting samples sent to us. This will help with our survey efforts and eventual varietal recommendations.

Tar Spot Update

Figure 2. A Screen shot of a map developed in the Field Prophet app showing risk for tar spot development in Wisconsin as of July 27, 2023.

You can find the most recent updates on tar spot confirmations across the U.S. here: https://corn.ipmpipe.org/tarspot/.  Tarspotter is also showing mostly moderate to high risk across the state of Wisconsin (Fig. 2). This means you should be actively scouting for tar spot at this time. The risk is likely that you will find it across much of the state. If the corn growth stage is between VT/R1 and R3, then you might go ahead and consider a fungicide application. Our research has shown that one well-timed application of fungicide somewhere between VT/R1 – R3 will control tar spot enough for a yield response even in a heavy-pressure year. You can learn more about managing tar spot by clicking here. If you think you found tar spot I would appreciate if you would let us know. We can enter the county level data into the Corn IPMPipe Map and contribute to the cause.

White Mold Update

Figure 3. Sporecaster predictions for selected non-irrigated locations in Wisconsin for July 27, 2023.

The risk for white mold according to Sporecaster is a bit more spotty, compared to tar spot. Mostly the northern tier of the state is at high risk while central and southern Wisconsin varies from moderate to low (Fig. 3). If you are in a low-risk area and you are at R3 or beyond, you might not have much to worry about for this year when it comes to white mold. However, if you are in a moderate-risk zone, watch this situation carefully. If you are at R3 and the crop has good canopy, you might consider one late R3 application. If you are in a high-risk zone, the crop has canopied, and your soybean crop is in the bloom period, it is time to think about a fungicide application. The recent rains have made the risk in these areas generally stay high or increase. These will be the areas I would expect to find white mold 1-3 weeks from now. If you would like to learn more about white mold management, check out my previous article HERE.

As always, get out and look the crop. Scout, scout, scout!

Wisconsin Field Crops Disease Update, July 12, 2023

/in , , , /by

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

Here is southern Wisconsin we are finally getting some rains. These rains are appreciated and timely for the crops out there, but also timely for some important pathogens of wheat, corn, and soybeans. Let’s talk about where we are at with disease risk this week.

What’s up with Wheat?

Let’s talk first about wheat first. Folks have started harvesting the crop and bailing straw and I have been getting photos of sooty mold on heads. You can find out more about sooty molds on wheat by clicking here. Essentially sooty mold is caused by a number of opportunistic fungi that can come in and cause mostly aesthetic problems on wheat heads that might have matured early, died early, or had other stress. These fungi do not need to be controlled. However, you should harvest affected wheat as soon as possible. Occasionally if wheat with sooty mold is left in the field for a long time, these fungi can eventually find their way in to the kernel and cause a problem called black point which can lead to quality problems. Get out and get that crop in as fast as you can!

Should I be Spraying for Tar Spot?

Figure 1. A Screen shot of a map developed in the Field Prophet app showing risk for tar spot development in Wisconsin as of July 12, 2023.

The short answer is not yet! Be patient. Yes, there have been many recent confirmations of the disease across the Midwest. You can find the most recent updates on tar spot confirmations here: https://corn.ipmpipe.org/tarspot/.  Tarspotter is also showing mostly high risk across the state (Fig. 1). This means you should get out and scout! Remember, the best time to spray fungicide for tar spot is between the VT and R3 growth stages. We are not quite there yet and need to be patient to maximize the performance of our fungicides. You can learn more about managing tar spot by clicking here. If you think you found tar spot I would appreciate if you would let us know. We can enter the county level data into the Corn IPMPipe Map and contribute to the cause.  Again, be patient and get out there and scout and get your steps in!

What to Do About Soybean White Mold?

Figure 2. Sporecaster predictions for selected non-irrigated locations in Wisconsin for July 12, 2023.

Yeah, it’s bean dry, yeah soybeans are slow to canopy. If you didn’t plant soybeans in narrow rows, you need to be patient and let soybeans get to full canopy. If this happens before the R3 growth stage, then check Sporecaster and see what the risk is. As of today, risk is low to moderate in south and south-central Wisconsin, Southwest Wisconsin, while in east and northeast Wisconsin risk is high if soybeans are flowering and canopy is nearly closed (Fig. 2). Again, I know it has been dry, but we are getting some timely rains that are impacting risk and resulting in the increase in risk. I do think that we can be patient and wait to the R3 growth stage to make the fungicide application decision. Our data suggest that this is the best time to spray for white mold in Wisconsin in recent years. If you would like to learn more about white mold management, check out my previous article HERE.

It’s the 2023 Field Season and I have White Mold on My Mind

/in , , , , /by

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

Shawn Conley, Extension Soybean and Small Grains Agronomist, Department of Agronomy, University of Wisconsin-Madison

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

Paul Mitchell, Extension Economist, Agricultural and Applied Economics, University of Wisconsin-Madison

Figure 1. Apothecia, a small mushroom-like structure of the white mold fungus that give rise to spores, which infect soybean flowers.

In Wisconsin, the first couple of weeks of July brings us a heightened awareness of white mold in soybeans, and its management. The 2022 season in Wisconsin resulted in some pockets of white mold in the state. If the weather becomes conducive in 2023, do get caught being complacent even though it seems to be too dry for white mold right now.

Remember that the white mold fungus infects soybeans through open and senescing flowers, by spores that are born from small mushroom-like structures called apothecia (Fig. 1). Remember that if the bloom period gets extended due to cool weather, this can lead to an extended window for infection by the fungus. Often cool weather is a double whammy as it is good for the white mold fungus and slows down soybean crop development, thereby extending bloom. Watch out if the weather suddenly changes!

While conditions have been hot and dry across most of the state, cooler and wetter weather could prevail in coming weeks. Currently the risk is high for much of the state, but falling rapidly due too dry conditions (Fig. 2). The white mold situation can change rapidly based on weather, thus anticipating favorable conditions for white mold, can help you protect your soybean crop.

Predicting White Mold 

The flowering growth stages are a critical time to manage white mold in-season. You can view a fact sheet and 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, 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 apothecia. These models predict 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. To facilitate precise predictions and make the model user-friendly, we use the Sporecaster smartphone application for Android and iPhone and also the Field Prophet app for iPhones.

Figure 2. Sporecaster predictions for selected non-irrigated locations in Wisconsin for July 5, 2023.

The purpose of the smartphone app is to assist farmers in making early season management decisions for white mold in soybean. The best time to spray fungicides for white mold is during flowering (R1 and R3 growth stages) when apothecia are present on the soil surface. If you have trouble growth-staging soybeans, here is a helpful guide on correctly identifying soybean growth stages.

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.

University research has indicated that the appearance of apothecia can be predicted using weather data and a threshold of percent soybean canopy row closure in a field. Based on these predictions and crop phenology, site-specific risk values are generated for three scenarios (non-irrigated soybeans, soybeans planted on 15″ row-spacing and irrigated, or soybeans planted on 30″ row-spacing and irrigated). Though not specifically tested we would expect row-spacings of 22 inches or less to have a similar probability response to fungicide as the 15 inch row-spacing.

The Sclerotinia apothecial models that underlie the Sporecaster prediction tool have undergone significant validation in both small test plots and in commercial production fields. In 2017, efficacy trials were conducted at agricultural research stations in Iowa, Michigan, and Wisconsin to identify fungicide application programs and thresholds for model implementation. Additionally, apothecial scouting and disease monitoring were conducted in a total of 60 commercial farmer fields in Michigan, Nebraska, and Wisconsin between 2016 and 2017 to evaluate model accuracy across the growing region. Across all irrigated and non-irrigated locations predictions during the soybean flowering period (R1 to early R4 growth stages) were found to explain end-of-season disease observations with an accuracy of 81.8% using the established probability thresholds now programmed in the app. We have made additional improvements for 2022, to further refine accuracy. So if you have used Sporecaster before, you might want to check the version in the “Help and Info” button to be sure you have version 1.41.3 of Sporecaster.

Not only can users run predictions of risk during the soybean bloom period for any field, you can also set up visual maps to look at multiple sites simultaneously. An example for the state of Wisconsin can be found in figure 2, which represents risk for July 5, 2023 for non-irrigated soybeans. Currently, if soybeans are flowering, risk is moderate to high in much of Wisconsin for non-irrigated soybeans, continued hot and dry weather is pushing the risk lower however. So continue to monitor this situation closely each day.

What to Spray for White Mold?

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. In Wisconsin, we have observed that Endura applied as a single application at 8 oz between the R1 and R2 growth stage performs well. Other fungicide options also include Omega and Proline. You can view results of past fungicide evaluations for Wisconsin by CLICKING HERE. If you would like to run tailored estimations of return on investment for various fungicide programs, you can use another smartphone application called Sporebuster.

What is Sporebuster?

When a fungicide application is needed to control white mold in soybeans, Sporebuster can help determine a profitable program. You enter your expected soybean price, expected yield, and treatment cost. Sporebuster instantly compares ten different treatment plans at once to determine average net gain and breakeven probability of each. You can mark, save and share by email, the best plans for your farming operation.

The purpose of Sporebuster is to assist soybean farmers in making a fungicide program decision that is profitable for their operation. Sporebuster is meant to complement Sporecaster. Once Sporecaster recommends a fungicide application, Sporebuster can be used to determine a profitable program.

Information that drives Sporebuster is based on research from 2009-2016 from across the upper Midwestern US. Statistical models were developed based on these data that included white mold pressure and yield response from fungicide for 10 common fungicide programs. Due to recent changes in the markets, be sure to manually adjust the cost of the product you are interested in, so that the tool returns an accurate estimate of return on investment. My advice is to call local suppliers and see what products you can get and what the per acre cost will be to get the application done. Details about the research behind Sporebuster can be found by CLICKING HERE.

Helpful Smartphone Application Links

Sporecaster

  1. Click here to download the Android version of Sporecaster. 
  2. Click here to download the iPhone version of Sporecaster.
  3. Click here to download the Field Prophet version of Sporecaster for the iPhone.

Sporebuster

  1. Click here to download the Android version of Sporebuster.
  2. Click here to download the iPhone version of Sporebuster.
  3. Here is a video on how to use Sporebuster and interpret the output.

Other Resources

  1. To watch an in-depth video on white mold management, CLICK HERE.
  2. To find more information on white mold, view a web book from the Crop Protection Network, CLICK HERE.

Scientific References

  1. Willbur, J.F., Fall, M.L., Blackwell, T., Bloomingdale, C.A., Byrne, A.M., Chapman, S.A., Holtz, D., Isard, S.A., Magarey, R.D., McCaghey, M., Mueller, B.D., Russo, J.M., Schlegel, J., Young, M., Chilvers, M.I., Mueller, D.S., and Smith, D.L. Weather-based models for assessing the risk of Sclerotinia sclerotiorum apothecial presence in soybean (Glycine max) fields. Plant Disease. https://doi.org/10.1094/PDIS-04-17-0504-RE
  2. Willbur, J.F.,Fall, M.L., Byrne, A.M., Chapman, S.A., McCaghey, M.M., Mueller, B.D., Schmidt, R., Chilvers, M.I., Mueller, D.S., Kabbage, M., Giesler, L.J., Conley, S.P., and Smith, D.L. Validating Sclerotinia sclerotiorumapothecial models to predict Sclerotinia stem rot in soybean (Glycine max) fields. Plant Disease. https://doi.org/10.1094/PDIS-02-18-0245-RE.
  3. Fall, M., Willbur, J., Smith, D.L., Byrne, A., and Chilvers, M. 2018. Spatiotemporal distribution pattern of Sclerotinia sclerotiorum apothecia is modulated by canopy closure and soil temperature in an irrigated soybean field. Phytopathology. https://doi.org/10.1094/PDIS-11-17-1821-RE.
  4. Willbur, J.F., Mitchell, P.D., Fall, M.L., Byrne, A.M., Chapman, S.A., Floyd, C.M., Bradley, C.A., Ames, K.A., Chilvers, M.I., Kleczewski, N.M., Malvick, D.K., Mueller, B.D., Mueller, D.S., Kabbage, M., Conley, S.P., and Smith, D.L. 2019. Meta-analytic and economic approaches for evaluation of pesticide impact on Sclerotinia stem rot control and soybean yield in the North Central U.S. Phytopathology. https://doi.org/10.1094/PHYTO-08-18-0289-R.

2022 Wisconsin Fungicide Test and Disease Management Summary Now Available!

/in , , , , , /by

Brian Mueller, Researcher II, UW-Madison, Plant Pathology

Damon Smith, Associate Professor and Extension Specialist, UW-Madison, Plant Pathology

Each year the Wisconsin Field Crops Pathology Program conducts a wide array of fungicide and disease management tests on alfalfa, corn, soybeans, and wheat. These tests help inform researchers, practitioners, and farmers about the efficacy of certain fungicide products on specific diseases and how to pair them with other disease management strategies. We hope you find this report useful in making decisions for the 2023 field season.

The 2022 Wisconsin Field Crops Fungicide Test and Disease Management Summary is available by clicking here. These tests are by no means an exhaustive evaluation of all products available, but can be used to understand the general performance of a particular fungicide in a particular environment. Keep in mind that the best data to make an informed decision, come from multiple years and environments. To find fungicide performance data from Wisconsin in other years, visit the Wisconsin Fungicide Test Summaries page. You can also consult publication A3646 – Pest Management in Wisconsin Field Crops to find information on products labeled for specific crops and efficacy ratings for particular products. Additional efficacy ratings for some fungicide products for corn foliar fungicides, soybean foliar and seed-applied fungicides, and wheat foliar fungicides can be found on the Crop Protection Network website.

Mention of specific products in these publications are for your convenience and do not represent an endorsement or criticism. Remember that this is by no means a complete test of all products available.  You are responsible for using pesticides according to the manufacturers current label. Some products listed in the reports referenced above may not actually have an approved Wisconsin pesticide label. Be sure to check with your local extension office or agricultural chemical supplier to be sure the product you would like to use has an approved label.  Follow all label instructions when using any pesticide. Remember the label is the law!

Are My Fungicides Messing with the Good (Microbes) Guys?

/in , , , /by

The following blog post was written as a part of a graduate level class assignment at the University of Wisconsin-Madison. Of course much more work needs to be done in this area, but there is some interesting “food for thought” and should be considered the next time you might want to spray a fungicide.    ~Damon Smith, Professor and Extension Specialist

 

Kelly Debbink, master’s student, Department of Plant Pathology, University of Wisconsin-Madison

Have you ever wondered if fungicides can negatively impact soil microbes? Since their job is to kill fungi, it seems logical that they may have this effect on the fungi in the soil, right? This thought process is exactly what led me into reading a few too many published studies related to the topic.

Background

Let me start with a bit of what we know about soil microbes (mainly fungi and bacteria). Some microbes form symbiotic relationships with plants, through which they can colonize the root system (rhizosphere), the above ground plant surfaces (phyllosphere), and even internal tissues (endosphere). These microbes can help plants access nutrients and water, fight off diseases caused by other pathogenic microbes, and deal with stressful environments. Many other types of microbes may not form direct relationships with plants, but still live in the soil and provide services, like breaking down nutrients.

To carry out many of these useful activities, microorganisms produce diverse groups of enzymes. They are proteins that work to facilitate different processes and are necessary in many services related to soil health, including decomposing organic matter, nutrient cycling, and degrading hazardous compounds. Enzyme amounts are sensitive to environmental factors like pH and soil organic matter as well as management practices like crop type, chemical use, and fertilizer use. Any alteration of the soil microbial community will lead to changes in enzyme production, so they are commonly used as a soil health indicator. Lower enzyme levels are generally tied to less fertile soil and less productive crops.

So, if microbes are responsible for all these services, could we be causing them harm and hindering some of these services when we apply fungicides?

In my search I was specifically hoping to find field research instead of lab research, so I could find information that was a closer proximation to real life conditions. I will admit that most studies I found on this topic were performed in the lab by removing soil from an agricultural region, dosing it with fungicides, and running soil health tests on it. I did find a few field studies in which treated and non-treated plots were compared in normal cropping systems. These studies were all a bit different in their approaches to measuring changes, and they tested many different fungicides with different modes of action, so I would not compare these studies side-by-side to each other, but I will share some general trends that appeared in their results.

Soil Microbes

To start, there do appear to be shifts in some of the fungal and bacterial communities related to fungicide treatments. In a study that looked at seed coatings (fungicides & insecticides), these did not appear to decrease the richness (total # of microbe species) but did shift the abundance of different groups of microbes. In another study, the number of culturable bacteria and fungi were decreased, which at least suggested a decrease in richness of the subset of microbes that are culturable on lab media. Other lab experiments showed declines or shifts in the fungal community, but differing results on the bacterial community (they may decline as well or may increase). In some conditions, bacteria may be able to thrive once they have decreased competition from fungi. In one field trial, the label application rate and 2x the label rate led to short-term declines in measures of viable microbes. These declines all recovered by harvest. Additionally, this study tested 10x the label rate, but in this treatment, microbes remained low through harvest.

Soil Enzymes

Shifts in soil enzymes related to microbial activity and nutrient cycling were observed in multiple field trials. The general trend appears to be that at lower fungicide application levels, like label rate and twice the label rate, these enzymes may shift up and down, but often return near normal levels by harvest time. In contrast, the study that applied 10x the label rate observed declines in most enzymes that did not recover by harvest. This suggests that improper overuse or accumulation of fungicides may be detrimental to soil functions like nutrient cycling.

Conclusion

Overall, there are many environmental conditions that play a role in soil fungal and bacterial populations and enzyme activity. Many management decisions can have an impact on these, like crop rotation, tillage, and fertilizer use. Chemical use, like fungicides and other types of pesticides, likely also play a role in at least short-term shifts in soil microbes and enzyme activity. Obviously, the main goal of these fungicides is to control disease, and they are certainly a useful and necessary tool to protect crop yields and minimize disease. However, these studies do help remind us that there can be negative soil health effects to their overuse, in addition to the increased risk of pesticide resistance. It’s a good reminder that fungicides are only one tool in the toolbox, and other management decisions like choosing resistant varieties can help us control disease with fewer necessary fungicide applications.

 

References:

Background

Turner TR, James EK, Poole PS. The plant microbiome. Genome Biol. 2013 Jun 25;14(6):209. doi: 10.1186/gb-2013-14-6-209. PMID: 23805896; PMCID: PMC3706808.

Chettri, D., Sharma, B., Verma, A. K., & Verma, A. K. (2021). Significance of Microbial Enzyme Activities in Agriculture. Microbiological Activity for Soil and Plant Health Management, 351–373. https://doi.org/10.1007/978-981-16-2922-8_15

Field Trials

Hou, K., Lu, C., Shi, B., Xiao, Z., Wang, X., Zhang, J., Cheng, C., Ma, J., Du, Z., Li, B., & Zhu, L. (2022). Evaluation of agricultural soil health after applying pyraclostrobin in wheat/maize rotation field based on the response of soil microbes. Agriculture, Ecosystems & Environment, 340, 108186. https://doi.org/10.1016/j.agee.2022.108186

Saha, A., Pipariya, A., & Bhaduri, D. (2016). Enzymatic activities and microbial biomass in peanut field soil as affected by the foliar application of tebuconazole. Environmental Earth Sciences, 75(7). https://doi.org/10.1007/s12665-015-5116-x

‌ Nettles, R., Watkins, J., Ricks, K., Boyer, M., Licht, M., Atwood, L. W., Peoples, M., Smith, R. G., Mortensen, D. A., & Koide, R. T. (2016). Influence of pesticide seed treatments on rhizosphere fungal and bacterial communities and leaf fungal endophyte communities in maize and soybean. Applied Soil Ecology, 102, 61–69. https://doi.org/10.1016/j.apsoil.2016.02.008

‌Lab Experiments

Han, L., Xu, M., Kong, X., Liu, X., Wang, Q., Chen, G., Xu, K., & Nie, J. (2022). Deciphering the diversity, composition, function, and network complexity of the soil microbial community after repeated exposure to a fungicide boscalid. Environmental Pollution, 312, 120060. https://doi.org/10.1016/j.envpol.2022.120060

‌ Cycoń, M., Piotrowska-Seget, Z., & Kozdrój, J. (2010). Responses of indigenous microorganisms to a fungicidal mixture of mancozeb and dimethomorph added to sandy soils. International Biodeterioration & Biodegradation, 64(4), 316–323. https://doi.org/10.1016/j.ibiod.2010.03.006