Fusarium Head Blight in Wisconsin Winter Wheat: A Guide for Harvest Preparation

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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

This season, we’ve observed moderate to high levels of Fusarium head blight (FHB), also known as scab, in some Wisconsin winter wheat fields. The incidence and severity have varied based on location, the susceptibility of the wheat variety, and whether a fungicide was applied at or shortly after anthesis.

FHB has been more prevalent in the southern and south-central wheat-growing areas of the state. However, it can also be found in other areas, depending on the susceptibility of the wheat varieties grown. As you prepare for harvest, it’s crucial to scout your maturing wheat crop and estimate the potential damage from FHB.

FHB can cause direct yield loss, and the fungus that causes this disease can also produce deoxynivalenol (DON), also known as vomitoxin.

Identifying FHB

Figure 1. Fusarium head blight of winter wheat

In non-mature winter wheat or spring wheat fields, diseased spikelets on an infected grain head die and bleach prematurely, while healthy spikelets on the same head retain their normal green color (Fig. 1). Over time, premature bleaching of spikelets may progress throughout the entire grain head. If infections occur on the stem immediately below the head, the entire head may die. As symptoms progress, developing grains are colonized, causing them to shrink and wrinkle. Infected kernels often have a rough, sunken appearance and range in color from pink or soft gray to light brown. As wheat dries down, visual inspection of heads for scab will become more difficult.

Why FHB Identification is Important

FHB identification is important because it not only reduces yield but also decreases the quality and feeding value of grain. The FHB fungus may produce mycotoxins, including DON or vomitoxin, which can adversely affect livestock and human health when ingested.

The U.S. Food and Drug Administration has set maximum allowable levels of DON in feed for various animal systems. For beef and feedlot cattle and poultry, the limit is less than 10 ppm; for swine and all other animals, it’s less than 5 ppm. However, many professional animal nutritionists agree that in ruminating cattle, the level of DON in the total ration should be below 1 ppm.

Local grain elevators test for DON and discount loads of grain for unacceptable levels of the mycotoxin. Be sure to check with your local elevator about their thresholds for docking grain and discount schedule based on the level of DON detected BEFORE you bring a load for delivery.

Lodged Wheat and DON

We’ve noted many fields with high levels of lodging in Wisconsin this season. Research has shown that DON levels are significantly higher in lodged wheat compared to standing wheat. The longer wheat is lodged, the more DON accumulates. If you suspect that DON is a concern in your field and there is significant lodging, care should be taken during harvest to test grain for DON.

Preparing for Wheat Harvest

  1. Adjust combine settings to blow out lighter seeds and chaff. Research has shown that adjusting a combine’s fan speed from 1,375 to 1,475 rpms (100 rpms above standard configuration) and shutter opening to 90 mm (3.5 inches; 20 mm wider than the standard configuration) resulted in the lowest discounts at the elevator due to low test weight, percentage of damaged kernels, and level of the mycotoxin deoxynivalenol (DON; vomitoxin) present in the harvested grain. This strategy should be used only for fields expected to have high levels of scab, as harvested yield can also be reduced in field with normal kernels due to the higher air flow.
  2. Take special care when harvesting fields that are lodged. Remember that higher levels of DON are likely in fields with lodged wheat. Be sure to test grain so you know what the DON concentration is before taking the crop to the elevator.
  3. Know your elevator’s inspection and dockage procedure and discount schedule (each elevator can have a different procedure and discount rate).
  4. Scabby kernels do not necessarily mean high DON levels and vice versa. For example, in a 2014 fungicide evaluation, very low visible levels of FHB were observed for all treatments. However, when the finished grain was tested for DON, significant levels were identified for all treatments. Be sure to test and know what levels of DON are in your grain even if you didn’t see a high level of visible disease. Also, don’t assume that because a fungicide was used, there will be no DON.
  5. DON can be present in the straw, so there is concern regarding feeding or using scab-infected wheat straw. DO NOT use straw for bedding or feed from fields with high levels of scab. If in doubt, have the straw tested for DON levels.
  6. Do not save seed from a scab-infected field. Fusarium graminearum can be transmitted via seed. Infected seeds will have decreased growth and tillering capacity as well as increased risk for winterkill.
  7. Do not store grain from fields with high levels of scab. DON and other mycotoxins can continue to increase in stored grain.
  8. Harvest in a timely fashion to minimize elevator discounts and balance dockage due to FHB. Click here to read about some recent research on optimizing harvest timing in winter wheat.

For more information on Fusarium head blight research, click here.

References

  1. Bissonnette, K.M., Kolb, F.L., Ames, K.A., and Bradley, C.A. Effect of Fusarium head blight management practices on mycotoxin accumulation of wheat straw. Plant Dis. 102:1141-1147.
  2. Cowger, C., and Arellano, C. 2013. Fusarium graminearum infection and deoxynivalenol concentrations during development of wheat spikes. Phytopathology 103:460-471.
  3. Nakajima, T., Yoshida, M, and Tomimura, K. 2008. Effect of lodging on the level of mycotoxins in wheat, barley, and rice infected with Fusarium graminiearum species complex. J. Gen. Plant Pathol. 74:289-295.
  4. Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Dis. 95:1448-1457.

Wisconsin Winter Wheat Disease Update – May 16, 2024

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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?

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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!

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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, July 12, 2023

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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.

Wisconsin Winter Wheat Disease Update – May 31, 2023

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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)

2022 Wisconsin Fungicide Test and Disease Management Summary Now Available!

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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?

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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

 

2022 Badger Crops and Soils Update Meetings

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The annual UW Agronomy, Pest Management and Soil, Water, and Nutrient Management meetings are moving to a new format this year and will be offered as a single day-long program. Two in-person sessions as well as a virtual option will be offered. In-person sessions in Green Bay and La Crosse will follow the same agenda. The virtual option will follow a similar but abbreviated agenda.

This year’s program will be focused on the theme of “Achieving a Positive Return on Investment in an Era of High Input Costs (a.k.a Small steps, Big change).” The meetings will present the latest information on agronomic, pest, and nutrient management research coming out of UW with a lens to on-farm application.

For details and to register for the event, please CLICK HERE or scan the QR code in the attached flyer. We are looking forward to seeing you and kicking off a busy winter meeting season!

Wisconsin Winter Wheat Disease Update – June 1, 2022

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

In Wisconsin, wheat diseases have been nearly non-existent up to this point. Cool weather has generally kept wheat disease at low levels. However, increase frequency of rain events and moderate temperatures over the next 7-10 days will likely increase disease risk, especially Fusarium head blight (FHB or Scab). 

Fusarium head blight risk for susceptible winter wheat varieties for June 1, 2022.

We are entering the window for fungicide applications for FHB here in Wisconsin. Currently the Fusarium Head Blight Risk tool is predicting more areas of moderate to high risk in Wisconsin for FHB than it did a week ago (Fig. 1). If highly susceptible wheat varieties were planted in Wisconsin, the current risk is high across most of the state. Rainy conditions in the next seven days will likely push this risk higher. Now is the time to consider a fungicide application to manage FHB in Winter wheat in the state.

In winter wheat in Wisconsin, research has demonstrated that the best time to apply fungicides is between the start of anthesis (first anthers out) to 7 days after the start of anthesis. This same research has demonstrated that waiting to apply fungicides 5 days after the start of anthesis, optimizes deoxynivalenol (DON or vomitoxin) reductions in finished wheat. This is due to the fact that head emergence in Wisconsin can be very uneven. Waiting 5 days after the start of anthesis may help with optimizing application timing to maximize heads flowering and receiving fungicide protection. Fungicide choice is also critical, with Prosaro, Caramba, and Miravis Ace providing the most consistent control of Fusarium head blight and reduction of DON in trials in Wisconsin. Fungicides containing strobilurin fungicides should be avoided after the boot stage of wheat as these products can increase DON levels in finished grain. Fungicide efficacy information from Wisconsin can be found at https://badgercropdoc.com/research-summaries/. National ratings for fungicide efficacy of small grains can be found HERE. Additional thoughts on using fungicide on wheat can be found in this Bumper Crops Video.

We also know that in Wisconsin, that a fungicide application targeted to manage FHB will pay for itself almost every time. You can find published research information on the probability of a return on fungicide investment by clicking HERE. Be sure to focus on comparing the “current” level of treatment to the “mid-level” of treatment in the publication. The only difference between these two treatment plans was the application of fungicide at Feekes 10.5.1 to manage FHB. The “mid-level” plan returned on average more than $120 per acre above the “current” management plan in our trials.

Keep scouting!