Wisconsin Winter Wheat Disease Update – May 24, 2024

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

Figure 1. Stripe rust on a flag leaf of winter wheat.

Winter wheat in Wisconsin continues to move through growth stage ahead of average. This week I have seen many wheat heads emerged and anthers out. We have also confirmed stripe rust (Fig. 1) in Columbia and Dodge Counties. Now is the time to make a decision on a fungicide application in winter wheat.

In my previous post I mentioned the importance of balancing both stripe rust and Fusarium head blight (FHB) as we moved into the next several weeks. Now that anthers are emerging on wheat heads, the time is right to get a fungicide application out to control FHB. These fungicides will also control stripe rust. You can find an excellent list of fungicides that will control both FHB and stripe rust HERE.

Given the current stripe rust movement into the state (Fig. 2) and potential risk for FHB to increase (Fig. 3), I think a fungicide should be strongly considered to protect yield in winter wheat this season. I realize that the Fusarium risk tool is still showing much of Wisconsin in a low risk of FHB. However, with stripe rust moving in at this point and the rainy weather, choosing an FHB fungicide to apply now at anthesis is a wise decision in my opinion. The optimal timing of application of fungicide at this point in the season is the start of anthesis (50% of heads showing at least one anther) to 7 days after the start of anthesis. This will maximize control of FHB while also providing control of stripe rust and the mycotoxin deoxynivalenol (DON).

Figure 2. U.S. counties confirmed to have stripe rust on wheat – May 24, 2024.

 

Figure 3. Risk of Fusarium head blight based on the Fusarium risk tool – May 24, 2024.

As always, be sure to get out in the field and scout, scout, scout! Making an informed decision is key to success!

Wisconsin Winter Wheat Disease Update – May 16, 2024

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

Winter wheat in Wisconsin continues to move through growth stages at record pace. We are about 10-14 days ahead on growth stages compared to this time in most years in Wisconsin. The warm spring and timely rain has pushed wheat very quickly.

As I mentioned last week, we continue to monitor the stripe rust situation. This week brings us a confirmed stripe rust positive in Tippecanoe Co. Indiana (Fig. 1). As I mentioned in my previous article, the likelihood is high that we will see stripe rust in Wisconsin this season. We have continued to scout for this disease and visited several variety and research location this week in southern Wisconsin. We have not found stripe rust yet. This doesn’t mean that it isn’t here. I still encourage you to scout and let us know if you find it or get it confirmed by our Plant Disease Diagnostic Clinic.

With the rapid growth stage changes happening, we are quickly approaching the time in the season that we need to be aware of risk and in-season management decisions for Fusarium head blight. Fusarium head blight (FHB) has typically been a more frequently occurring issue in Wisconsin. However, in recent years, our spring seasons have been exceptionally hot and dry leading to little disease. However, this season is different with moderate temperatures and adequate precipitation to make FHB an issue. Not only is the disease yield limiting, but the fungus that causes FHB can also produce the mycotoxin called deoxynivalenol (DON or vomitoxin). DON contamination above 2 ppm in finished grain can often lead to discounts at the elevator or outright rejection. Thus, this disease is worth managing.

Fortunately, we have some excellent in-season management options for FHB. Be sure you know the relative susceptibility of the varieties you have planted. We have excellent data showing significant reductions of FHB where we use a resistant variety and then layer a fungicide application on top. Varietal resistance works!

When it comes to fungicides for FHB, there are really just five products to choose from that are rated as “Good” on the Fungicide Efficacy for Control of Wheat Diseases table. Timing is everything when using a fungicide for FHB management. Be sure to time applications at the start of anthesis or within 5-7 days after the start. This is the ideal window of opportunity to control FHB and reduce DON levels in the finished grain. Spraying earlier than anthesis or later than about a week after the start of anthesis will result in lost efficacy, or no control of FHB. If you need help with growth staging, be sure to check out the “Visual Guide to Winter Wheat Development and Growth Staging.” Also, the fungicides rated “G” for FHB in the fungicide efficacy table are effective against stripe rust, so if that disease happens to move in now or later, a single application of fungicide at the anthesis timing should take care of both problems.

There is a disease prediction tool for FHB of wheat. You can find that tool at http://www.wheatscab.psu.edu. This tool should be monitored frequently as your crop approaches anthesis and soon after. It can help you determine if your crop is at risk, based on the weather conditions. Risk as of May 16, 2024 for FHB-suscpetible winter wheat varieties is currently estimated to be low (Fig. 2). However, given the 7-day forecast of rain and warm temperatures, I would suspect this to change to be more favorable for FHB risk in the coming 7-10 days. If you haven’t applied a fungicide yet this season, I would urge you to consider one, well-timed application targeting FHB this season.

The ‘Take Home’ for wheat management over the next several weeks.

  1. Plan to apply an FHB fungicide application – especially on susceptible varieties
  2. Shoot for Anthesis or up to 5-days after the start of anthesis for the fungicides rated “G” for FHB in this table.
  3. All of the available fungicides rated for FHB also are effective against stripe rust. Thus, one fungicide can manage both problems!
  4. You can go slightly earlier (Feekes 10.5; Efficacy slightly reduced compared to typical timing) up to 5-days after the start of anthesis for Miravis Ace to manage FHB.
  5. Watch the “Scab Alerts” – it isn’t perfect, but can help you make a decision (http://www.wheatscab.psu.edu).

Stripe Rust in Wisconsin in 2024?

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

The last several winter  wheat seasons in Wisconsin have been very quiet when it comes to disease. Hot and dry weather has meant that while the inoculum for some pathogens might be in Wisconsin, we haven’t seen any epidemics of disease that needed active in-season management. That could change in 2024 as we watch the stripe rust situation in the south and mid-south.

The current stripe rust Ag Pest Monitor shows numerous counties in Louisiana, Arkansas, and Kansas positive for the disease (Fig. 1). Most recently, Cumberland County Illinois was also found to be positive. This latest positive is the earliest we have seen stripe rust move up this far in the “rust pathway” in a few years. Given that the winter wheat crop in Wisconsin is not yet to flag leaf growth stages, we need to watch the progression of this disease carefully. We are about to come into a critical time of the season, that if we have active stripe rust, we will need to supply in-season management.

Stripe rust of wheat is caused by the fungus Puccinia striiformis. Stripe rust can be identified by orange/yellow pustules that typically occur in a striped pattern on the surface of the wheat leaf. However, under low severity, single, or very few sparsely spaced pustules may be observed. Subsequent infections can arise from a single pustule. Disease is favored by prolonged periods of rain (or dew), high relative humidity, and cool temperatures ranging from 50 to 60 ºF.

Management of stripe rust includes using resistant cultivars and applying fungicides. Although it is too late to make decisions on a cultivar, scouting should be prioritized to fields where you know there was a susceptible cultivar planted. Considering the early start to the stripe rust epidemic to our south, careful and frequent scouting will be critical this season. If stripe rust pustules are observed, consider sending samples to the University of Wisconsin Plant Disease Diagnostic Clinic for positive identification. If stripe rust is confirmed and it appears to be active, a fungicide application might be necessary.

In recent years in Wisconsin, we have not needed to apply a fungicide before the Fusarium head blight timing of Feekes 10.5.1. However, in years when stripe rust starts early, research has demonstrated that an application at the flag leaf emergence timing (Feekes 8) helps to protect grain yield. For more information on growth-staging wheat, check out the “Visual Guide to Winter Wheat Development and Growth Staging.”

In our work titled “Wheat grain and straw yield, grain quality, and disease benefits associated with increased management intensity” we found that years with intensive stripe rust epidemics (2016 and 2017) a fungicide application at Feekes 8, in addition to a second application of fungicide at Feekes 10.5.1, helped to protect yield at the end of the season. In years where there was no stripe rust, a Feekes 8 application of fungicide was not needed, but an application at Feekes 10.5.1 almost always provided a positive return on investment.

If you find stripe rust and are considering an application of fungicide at Feekes 8, you have lots of options of products. Be sure to consult the “Fungicide Efficacy for Control of Wheat Diseases” table (Fig. 2) to find products that provide excellent control of stripe rust. Be sure to check your local recommendations and also the label to verify the use of all products in your area. You can also check out our fungicide test reports HERE. Be sure to go back to the 2016 and 2017 era reports to find data on stripe rust, as those were the last years of epidemics suitable to obtain efficacy data on stripe rust.

As always, SCOUT, SCOUT, SCOUT!

2023 Wisconsin Fungicide Test and Disease Management Summary Now Available!

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

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

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

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

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.

What Should I do About Tar Spot of Corn in 2023?

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

Brian Mueller, Researcher II, Department of Plant Pathology, University of Wisconsin-Madison

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

It didn’t take long this year to find tar spot in the Midwest. Over the last several weeks we have seen confirmed positives for tar spot in parts of Iowa, Missouri, Kansas, and Nebraska (Fig. 1). This is earlier than last year despite. With that said, the severity is extremely low and does not necessitate spraying fungicide at the moment! So what should you do?

Figure 1. Map of U.S. counties where tar spot has been confirmed in the 2023 season, as of July 5, 2023. Map source: https://corn.ipmpipe.org/tarspot/.

What should I do?

My advice is to get prepared and make sure you have the tools in place to deal with this problem. As I said the last few seasons, tar spot is here to stay and we need to simply be prepared and ready to fight the disease. The first line of defense is to know if you have had tar spot before. This will tell you if there is resident inoculum sources present that can initiate epidemics. If you have seen tar spot on your farm before, then assume the pathogen is present and in close proximity to corn (the host). Remember the disease triangle? The last component of the triangle is the weather. If there has been conducive weather then the triangle has been met and risk is high for finding tar spots. So how do you know if the weather is conducive? Well, there is an app for that!

Tarspotter and Field Prophet are both Smartphone applications that can help you determine if the weather has been conducive to put your corn crop at high risk of tar spot development. Figure 2 shows a map of Wisconsin from the Field Prophet version of the tool that is showing that weather has been highly conducive for the development of tar spots. The app DOES NOT tell you if the pathogen is present. We are working on this part of the triangle to improve our predictions, but you need to determine if the pathogen is present in your field. This tool just tells you if the weather has been conducive.

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 5, 2023.

So what weather is conducive for tar spot development? You are probably asking yourself this as we are in an epic drought, yet the forecasted risk of tar spot is high across the state. Well conducive weather for the pathogen it is different that the weather needed to grow corn. Yes, precipitation is helpful, but more importantly, we need intermittent wet/dry cycles to give us intermittent leaf wetness. Specifically leaf wetness at night. What gives leaf wetness this time of year other than rain? That would be high dew points and humidity. These variables are included in the models that run in Tarspotter and Field Prophet. We also include temperature which is an influential variable too. These variables are measured over the last 14 days and 30 days and included in each daily run of the tool. We use the GPS on the smartphone to pull down cloud-based weather for a precise location. Thus, these results are site-specific. I also like to the use the Field Prophet version of the models as this version provides a 7-day trend line on how weather has been progressing and also allows for a true 7-day forecast. These additional tools can better help with the decision-making process. If you would like to learn more about the “nuts and bolts” that run behind the smartphone apps, you can find our research publication HERE.

My corn is at V10, should I spray Fungicide?

My short answer is no! The disease is just getting started. If you find it in Wisconsin right now, it will be at low severity and is low in the canopy on leaves that are not going to contribute to yield. My advice is to use your prior knowledge of where tar spot occurred and the Tarspotter tool to help guide your scouting efforts. Get out into the fields and know what you are dealing with. Figure 3 shows various severity levels on a corn leaf. We don’t start to see yield loss until we reach about 10% severity on the ear leaves or above. Thus, you have time! Target fields planted to known susceptible hybrids. Get yourself prepared and use those lower leaves to monitor severity and tar spot progress. Be ready to protect (put fungicide on) those leaves that contribute to yield (ear leaf and above), later on especially if the weather becomes increasingly conducive (think wet/dry cycles!) and/or your scouting indicates severity is increasing.

When should I spray fungicide? What should I use?

Figure 3. Tar spot severity diagram indicating various levels of tar spot on corn leaves. Yield loss isn’t typically detectable in the field until severity reaches 10% or more on the ear leaf or leaves above this leaf.

Our recent work has shown that if you get the product right, you can generally control tar spot to the point to preserve your yield potential, with one well timed spray. So what is that timing of the single application? That would be between the VT (tasseling) and R3 (milk) growth stages. We determined this using a series of trials where we did single applications of fungicide for individual growth stages. Figure 4 shows the results of two trials from 2020 where the window of opportunity to reduce the severity of tar spot with a single application is between VT and R3. Yes, the two-spray program (V8+VT) did also control tar spot, but all the work was done by the VT application, not the V8-timed spray! Thus, if you chose to spray your 2023 crop at this point in the season, you stand a good chance of having to come back with a second application later in the season.

Also notice in figure 4 that Tarspotter was tested in 2020 and did not perform very well. This was an early iteration of the tool and we have since improved its performance. So please don’t judge the tool based on this figure. If you would like to see how Tarspotter performed in advising fungicide applications last season, check out this article based on the 2021 field season.

Now the questions is what fungicide should you choose? The short answer is that you have lots of options. You can learn more about fungicides and fungicide performance by CLICKING HERE. You can also check out the efficacy of various fungicides based on a collective of University research by viewing the “Fungicide Efficacy for Control of Corn Diseases” on the Crop Protection Network website. In addition, Dr. Darcy Telenko at Purdue University led an effort to publish data from a multi-state coordinated fungicide trial where we tested various fungicides during the 2021 epidemic.

Figure 4. Tar spot intensity after spraying fungicide once at each corn growth stage during the 2020 field season.

 

Figures 5 shows the tar spot severity, while figure 6 the corn yield, from those trials where a single application of each of the products was made at the VT growth stage. Clearly you have lots of options when it comes to products that can control tar spot. That is good news! Yes, some products do a bit better in preserving yield over others, but all fungicides tested in 2021 resulted in numerically higher yields than not-treating. Remember that 2021 was a banner year for tar spot. These results might not be as clear in a year where tar spot is not as intense.

Figure 5. Tar spot severity from multi-state trials where corn was treated with foliar fungicides at the VT corn growth stage, or not treated. Source: Telenko et al., 2022 – https://apsjournals.apsnet.org/doi/10.1094/PHP-02-22-0012-BR.

Figure 6. Corn yield from multi-state trials where corn was treated with foliar fungicides at the VT corn growth stage, or not treated. Source: Telenko et al., 2022 – https://apsjournals.apsnet.org/doi/10.1094/PHP-02-22-0012-BR.

The Conclusion

DON’T PANIC! This is just a call to be ready. Download the apps and know what the weather is doing. Use your prior knowledge and scouting in key locations to track tar spot. Get your management plan in place. Have your fungicide of choice available. Communicate with your custom applicator. Be ready to spray between the VT and R3 growth stages if you plan to use just one fungicide application and you are seeing tar spot increase. If you spray between the V8 and VT growth stages, be ready to monitor the smartphone apps and do more scouting as you might have to pull the trigger again later in the season. Get out and SCOUT, SCOUT, SCOUT!

Other Resources

Wisconsin Winter Wheat Disease Update – May 31, 2023

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

Diseases of wheat in Wisconsin have basically been non-existent this season. Dry weather is leading to virtually no disease issue with the exception of one disease. Like 2021, powdery mildew is starting to show up on susceptible varieties. This one fungal disease likes to break the rules of cool and wet. Let’s discuss this disease further and then dig in a bit on what you should do for disease management as we move through the rest of the 2023 winter wheat season.

Figure 1. Signs and symptoms associated with powdery mildew on a wheat leaf.

So, what’s up with powdery mildew

Powdery mildew of winter wheat is caused by the fungus Blumeria graminis f. sp. tritici. The most notable sign of powdery mildew is the white, fluffy fungal growth that occurs on the surface of leaves (Fig. 1). Yellow spots may be present on the underside of the leaf. The white “tufts” might also have very small black pepper-like structures in them. Generally, the disease will start in the lower canopy, and if weather is favorable, will move up the canopy eventually reaching the flag leaf and even infecting heads on susceptible varieties.

The reason that powdery mildew has been an issue this year, despite the dry weather, is that it happens to like cool night-time conditions combined with high humidity and dew events. Warm days and cool nights often lead to dew and extended periods of leaf wetness (think semi-arid climates). This combined with temperatures less than 80 F, means the fungus can thrive on susceptible varieties where humidity has been high. Excessive rain events actually deter this particular fungus, as heavy rain events can wash spores from the leaf. So, it isn’t surprising that we are seeing powdery mildew right now given the weather we have had in parts of the state.

Should you spray fungicide for powdery mildew?

Most of the time I would say no. Often in Wisconsin, the weather begins to turn much warmer as we approach heading and the fungus will stop spreading and remain a novelty in the lower canopy. Remember, once daytime temperatures get above 80 F, the fungus will stop or slow in progression. The key in making the fungicide spray decision is to know the susceptibility of the variety you planted and watch the weather. If the weather remains conducive (temps below 80 F, no rain, but dew) and the variety is ranked susceptible, then spraying around flag leaf emergence might be warranted. You can consult the Fungicide Efficacy for Control of Wheat Diseases table for products rated with the best efficacy for powdery mildew. Note that most of the higher rated products are triazole compounds, or compounds with a triazole in their mix. No need to be fancy here, find something that fits your budget and has good efficacy. There should be ample choices.

Figure 2. FHB on some wheat heads. Note the bleached and reddened appearance of infected kernels.

I don’t care about powdery mildew, but what disease should I keep an eye on next?

Fusarium head blight (Fig. 2) has been a perennial problem for us in Wisconsin over the last few years. Not only have we seen significant damage and yield reductions due to the disease, but we have seen significant discounts at the elevator for levels of deoxynivalenol (DON or Vomitoxin) above 2 ppm. The one exception was 2021, which is sort of shaping up similar to 2023. However, it remains important to manage this disease actively here in Wisconsin.

Be sure you know the relative susceptibility of the varieties you have planted. We have excellent data showing significant reductions of FHB where we use a resistant variety and then layer a fungicide application on top. In 2019 we evaluated the susceptible variety, Hopewell, against the resistant variety, Harpoon. Figure 3 shows the FHB levels for the two varieties which were also subjected to a fungicide application. Clearly variety resistance works.

Figure 3. Fusarium head blight index (FHB Index) from a 2019 integrated management trial where the susceptible variety, Hopewell, and the resistant variety, Harpoon, were both treated with various fungicide programs or not treated with fungicide.

When it comes to fungicides for FHB, there are a few to choose from. These are Caramba, Prosaro, Miravis Ace, Prosaro Pro, and Sphaerex. Again the Fungicide Efficacy for Control of Wheat Diseases table shows the efficacy ratings of these products against FHB. Timing is everything when using a fungicide for FHB management. Be sure to time applications at the start of anthesis or within 5-7 days after the start. This is the ideal window of opportunity to control FHB and reduce DON levels in the finished grain. Spraying earlier than anthesis or later than about a week after the start of anthesis will result in lost efficacy, or no control of FHB. Also, these fungicides are effective against powdery mildew, so if that disease happens to be an issue for the variety you have chosen, a single application of fungicide at the anthesis timing should take care of both problems.

Should I spray for Fusarium head blight in 2023?

The answer to that question is a little complicated. However, there is a tool that can help with this decision. You can find the FHB prediction tool at http://www.wheatscab.psu.edu.This tool should be monitored frequently as your crop approaches anthesis and soon after. It can help you determine if your crop is at risk, based on the weather conditions. We are quickly approaching anthesis in the southern portion of Wisconsin. As of May 31, 2023, the risk for FHB in the whole state of Wisconsin is low, even on susceptible varieties. Again, dry weather leading up to this week has not been favorable for FHB. The 7-day forecast is also not looking conducive. Thus, the likelihood of a significant return on the fungicide investment is likely to be low this season. However, if you are risk adverse and would like to put an anthesis application of fungicide on, I would not be fancy with my choice. You might choose the cheapest product you can get ahold of, that is rated at least “G” on the fungicide efficacy table. This is not the season where you need to spend a lot of money on a fungicide, as the yield benefits are going to be lower due to the dry weather at heading. If you would like to study the performance of fungicide in wheat trials in Wisconsin, you can find trial data from my research going back 10 years by CLICKING HERE. Be sure to study multiple years and make sure a product was consistent in performance.

The ‘Take Home’ for wheat management over the next couple of weeks.

This can be cooked down to two main points. Here they are:

  • Don’t get too concerned about powdery mildew unless your variety is rated suscpetible
    1. If that is the case, then plan to apply a fungicide at anthesis for FHB (see below)
  • If you plan to apply an FHB fungicide application – especially on susceptible varieties
    1. Shoot for Anthesis or up to 5-days after the start of anthesis for any of the fungicides that are rated “G” in the fungicide efficacy table
    2. Can go slightly earlier (Feekes 10.5; Efficacy slightly reduced compared to typical timing) up to 5-days after the start of anthesis for Miravis Ace
    3. Watch the “Scab Alerts” – it isn’t perfect, but can help you make a decision (http://www.wheatscab.psu.edu)