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!

 

Wisconsin Winter Wheat Disease Update – May 24, 2022

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

Figure 1. Fusarium Head Blight Risk Map – May 24, 2022.

Winter Wheat is Wisconsin is in the “boot “or heading in the southern part of the state. Currently the Fusarium Risk Assessment Map is showing low risk for Fusarium head blight development (Fig 1). Rain is forecast for the next several days, thus, the risk is likely to climb as we approach wheat heading and flowering. Wheat farmers and consultants should pay attention to weather closely over the next several weeks as the decision to apply fungicide will need to be made during this time.

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 likely since 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.

Wisconsin Winter Wheat Disease Update – May 28, 2021

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

Figure 1. Fusarium head blight risk for susceptible winter wheat varieties for Wisconsin as of May 28, 2021.

Winter wheat in Southern and South-central Wisconsin is quickly approaching anthesis. By early next week the window of opportunity to apply fungicide for Fusarium head blight (FHB; scab) will be here. Currently the risk for FHB is variable and ranges from low to high depending on where you are in the state (Figure 1). Given the recent rain events and rising temperatures, I think the risk is there for FHB next week. This situation should be monitored closely and a timely fungicide application decision should be made. In my previous post, I talk about how to manage FHB.  There are essentially three options for products in Wisconsin for control of FHB. These include Prosaro, Caramba, and Miravis Ace. All also have efficacy against other foliar diseases too. Remember, your window of opportunity to spray for FHB ranges from the start of anthesis (flowering) to about 7 days after the start of anthesis.

Stripe rust still remains unidentified in the state. Confirmed reports of stripe rust are only as close as central Illinois (Figure 2). Continue to remain diligent in scouting for this disease. Remember that fungicides for control of FHB will also be efficacious for stripe rust. Thus, we should be able to “kill two birds with one stone” when spraying for FHB.

Figure 2. Confirmed stripe rust reports for the U.S. as of May 28, 2021.

Reports of powdery mildew continue to come in.  Remember that the FHB fungicide treatments will control this disease. So at this point, two applications of fungicide are not needed. A well-timed FHB-focused fungicide app should help slow powdery mildew.

Get out there and scout, scout, scout!

Managing Winter Wheat Diseases in Wisconsin During the 2021 Field Season

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

Up until this week diseases of winter wheat have been basically non-existent. Dry weather leading to a moderate drought in much of the state has meant that the environment has not been favorable for most wheat pathogens of concern for us in the upper Midwest. There is an exception to that rule, and we have observed one disease, and gotten reports of that disease this week. That disease is powdery mildew and does tend to follow a few different “rules” when it comes to fungal diseases. 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 2021 winter wheat season.

So, what’s up with powdery mildew?

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

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 conditions combined with 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. 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.

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.

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

The last few seasons, two diseases have been our primary focus on winter wheat in Wisconsin. These diseases are stripe rust and Fusarium head blight (scab or FHB). In 2019 and 2020, only FHB was yield limiting. However, in 2016 and 2017, we dealt with both stripe rust and FHB in the same season. Obviously, this year could be different, but the stripe rust situation is starting to “heat up” a bit to our south. The “Wheat Ag Pest Monitor for Stripe Rust”  indicates that there are confirmed cases of stripe rust in central Illinois (Fig. 2). This situation needs to be watched carefully over the next 1-2 weeks in Wisconsin.

 

Figure 2. Confirmed stripe rust observations in the U.S. as of May 19, 2021.

 

We are rapidly approaching the first growth stage where the application of fungicide might be warranted if stripe rust is found in your locale or is nearby. Based on recent published research, in years where stripe rust was active at the emerging flag leaf growth stage (Feekes 8), we obtained excellent control of stripe rust and a positive return on investment where we sprayed fungicide at this growth stage with a second application of fungicide for FHB control around anthesis.

Currently there is no stripe rust confirmed in Wisconsin but given the rainy weather recently and the positive confirmations in Illinois, this situation should be closely monitored, and a fungicide might be warranted on susceptible varieties if stripe rust is found prior to heading.

If you decide you need to apply a fungicide, there are many choices with decent efficacy against stripe rust. Again, consult the “Fungicide Efficacy for Control of Wheat Diseases” table for the best ratings for the disease. Find a product that is efficacious and fits your farm budget.

So, what should I do about Fusarium head blight?

Figure 3. Fusarium head blight of winter wheat

Fusarium head blight (Fig. 3) has been a perennial problem for us in Wisconsin over the last 5 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. It is 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 4 shows the FHB levels for the two varieties which were also subjected to a fungicide application. Clearly variety resistance works.

When it comes to fungicides for FHB, there are really just three products to choose from. These are Caramba, Prosaro, and Miravis Ace. 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 stripe rust, so if that disease happens to move in later, a single application of fungicide at the anthesis timing should take care of both problems.

 

Figure 4. 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.

 

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. While most wheat as of May 19, 2021 is not near heading yet in Wisconsin, you can see in figure 5 that for susceptible FHB varieties, the risk is currently low. Again, dry weather leading up to this week has not been favorable for FHB.

 

Figure 5. Fusarium head blight risk as of May 19, 2021 in the U.S.

 

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

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

  • In some years applying fungicides for stripe rust on susceptible cultivars around Feekes 8 will be needed. Make this decision based on the following:
    1. The known susceptibility of the variety
    2. Local presence of strip rust and/or confirmed reports nearby
    3. Favorable weather (frequent rains and temperatures less than 80 F)
  • 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 Prosaro and Caramba fungicides
    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)

 

Wisconsin Winter Wheat Disease Update – June 23, 2020

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

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

Figure 1. Septoria leaf blotch on a wheat leaf.

We are now well past the time to apply fungicide on winter wheat in Wisconsin. Anthesis has come and gone and now it is time to scout for the predominant diseases to start planning for harvest. We have not observed any symptoms of Fusarium head blight (FHB or scab) yet, but we will continue traveling and scouting.

We are beginning to observe increasing levels of foliar diseases on winter wheat in the state. Septoria leaf blotch (Fig. 1) is visible in the lower canopy and moving up the canopy in many fields we have been in, as weather remains wet and humid. Fungicide applications for FHB should slow the progress of Septoria leaf blotch up the canopy, but care should be taken to monitor the progress of this disease.

Figure 2. Barley yellow dwarf on winter wheat in Wisconsin. Note the purpled flag leaves.

We are also finding higher than normal levels of Barley yellow dwarf virus (BYDV) in winter wheat (Fig. 2). Levels of BYDV are between 5 and 10% incidence on some varieties in the uniform variety trials. Higher levels may be a result of earlier than normal aphid flights this spring due to mild conditions. Regardless, I don’t think there is a huge amount of concern, as many varieties are resistant and levels observed are still below that at which yield might be reduced.

Finally, we have observed Cephalosporium stripe on wheat at the Arlington uniform variety trial location (Fig. 3). We have seen this disease occurring more frequently in the state over the last couple of seasons. One reason might be shorter rotations between wheat in some fields and potentially increased susceptibility in some varieties. I would say that this season it isn’t severe as far as we have seen, but we will rate the disease and report results if they look meaningful. You will remember that in 2019, we had a severe epidemic of Cephalosporium stripe at our Sharon, WI uniform variety trial location. The severity ratings can be found in the trial report.

Figure 3. Cephalosporium stripe of winter wheat in Wisconsin.

We continue to look for stripe rust in the state. While we have found it at VERY low levels in a couple of locations, we have not seen increased occurrence or severity since the initial observations. Hot and dry weather has kept this disease under control. We will continue to scout wheat in the state and report the results of our observations here. Until then, get out and SCOUT, SCOUT, SCOUT!

Wisconsin Winter Wheat Disease Update – June 2, 2020

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

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

Figure 1. Fusarium Risk Tool prediction for FHB-susceptible varieties of winter wheat in Wisconsin on June 2, 2020.

Winter wheat in Wisconsin is moving through growth stages very rapidly over the past week due to ample moisture and heat. I have visited several fields this week with heads emerging or almost completely emerged. Anthesis (flowering) will begin in many winter wheat fields this week, if it hasn’t already started.

With the start of anthesis comes the critical time to consider a fungicide application for Fusarium head blight (FHB or scab). The Fusarium Risk Tool is showing very favorable conditions for the major wheat producing areas of Wisconsin, for susceptible varieties (Fig. 1). Risk is also medium-to-high in these zones for moderately susceptible varieties. Given the heat and high humidity with the multiple chances of rain predicted, a fungicide application may be warranted at this time in your winter wheat fields, especially if you have susceptible varieties.

Remember that the best time to apply a fungicide for FHB control is at the start of anthesis, up to 7 days after the start of anthesis. In Wisconsin, our research has demonstrated that we can significantly reduce the levels of deoxynivalenol (DON or vomitoxin) in finished grain if we wait until 5 days after the start of anthesis to apply our FHB fungicide. This is due to the fact that we often have uneven head emergence in our fields and delaying applications a few days after the start of anthesis can let these heads (or those on secondary tillers) “catch up.”

Fungicides considered most consistent in efficacy in University research include Prosaro®, Caramba®, and Miravis Ace®. Efficacy ratings for these and other products can be found on the Crop Protection Network’s Fungicide Efficacy for Control of Wheat Diseases fact sheet. Results from fungicide efficacy trials from the Badger Crop Docs, can be found BY CLICKING HERE. Research trials from 2019 that include the newest fungicide, Miravis Ace®, can be found BY CLICKING HERE and scrolling down to the last several pages. Remember, that the goal is to reduce damage by FHB and reduce DON levels as far below 2ppm as possible. The ideal method to do this includes an integrated approach of using resistant varieties and well-timed fungicide applications.

Figure 2. Stripe rust occurrence for a portion of the U.S. as of June 2, 2020

In our travels over the past week we also found stripe rust at very low levels in the Wisconsin Winter Wheat Variety trial located in Chilton, WI (Calumet Co.). We have documented this on the stripe rust monitor (Fig. 2). This was at low severity on flag leaves of known susceptible and moderately susceptible varieties of winter wheat. We have not observed stripe rust in the other variety trials in the state, or in other fields we have visited at this point. I believe that the high heat will keep stripe rust moving slowly. In addition, fungicide applications that will be applied for FHB control will also be effective in reducing the severity of stripe rust.

Now is the time to get out and SCOUT, SCOUT, SCOUT and make those educated fungicide spraying decisions!

Wisconsin Winter Wheat Disease Update – May 27, 2020

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

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

Figure 1. Fusarium Risk Tool prediction for FHB-susceptible varieties of winter wheat in Wisconsin on May 27, 2020.

Winter wheat in Wisconsin has responded to above average temperatures and rainfall, rapidly advancing through growth stages. In just a week or so, mainstems have rapidly elongated. In some varieties in southern and south-central Wisconsin, flag leaves are fully out. While now is a good time to consider a fungicide application, foliar disease has been non-existent in fields we have been in. We are monitoring the stripe rust situation carefully, and while it is active in states to our south, we have not observed any in fields we have scouted. The above average heat will also keep stripe rust moving slowly, especially in varieties with moderate resistance. So for now, I think we can hold off on fungicide. With margins being tight, I think it is wise to keep our fungicide application for Fusarium head blight (FHB or scab). Fungicides directed toward FHB are also effective against stripe rust, should it move in later in the season. Continue to scout fields between now and head emergence to catch any foliar diseases that might emerge.

Speaking of FHB, conditions have been VERY conducive for this disease in Wisconsin over the past week. The Fusarium Risk Tool is showing very favorable conditions for the entire state of Wisconsin for susceptible varieties (Fig. 1) and favorable conditions in the southern portion of the state for even moderately resistant varieties. This situation needs to be monitored over the next few days as heads start to emerge and anthesis (flowering) begins. Humid/wet and warm conditions will keep risk of FHB high as anthesis begins. We have also had several years of significant FHB and Gibberella ear rot in corn, meaning we have ample inoculum sources locally to initiate FHB epidemics. Farmers with winter wheat should be prepared to make a fungicide application if these conditions persist, especially those with wheat varieties rated as susceptible to FHB.

Remember that the best time to apply a fungicide for FHB control is at the start of anthesis, up to 7 days after the start of anthesis. In Wisconsin, our research has demonstrated that we can significantly reduce the levels of deoxynivalenol (DON or vomitoxin) in finished grain if we wait until 5 days after the start of anthesis to apply our FHB fungicide. This is due to the fact that we often have uneven head emergence in our fields and delaying applications a few days after the start of anthesis can let these heads (or those on secondary tillers) “catch up.”

Fungicides considered most consistent in efficacy in University research include Prosaro®, Caramba®, and Miravis Ace®. Efficacy ratings for these and other products can be found on the Crop Protection Network’s Fungicide Efficacy for Control of Wheat Diseases fact sheet. Results from fungicide efficacy trials from the Badger Crop Docs, can be found by CLICKING HERE. Research trials from 2019 that include the newest fungicide, Miravis Ace®, can be found by CLICKING HERE and scrolling down to the last several pages. Remember, that the goal is to reduce damage by FHB and reduce DON levels as far below 2ppm as possible. The ideal method to do this includes an integrated approach of using resistant varieties and well-timed fungicide applications. Continue to monitor the wheat disease situation closely and get out and Scout, Scout, Scout!

Timely Wheat Disease Management Video Series and Wheat Fungicide Information

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

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

Winter wheat in Wisconsin is finally starting to move along in growth stages. Warmer weather is helping to increase tillering. As wheat begins to move through growth stages, diseases and disease management will begin to be of concern. To assist in making wheat disease management decisions in Wisconsin, we have developed a 3-video series on the subject. Each video talks about making fungicide application decisions at the critical growth stages in for management in Wisconsin. The video series can be found below:

For information about fungicides and fungicide efficacy for winter wheat diseases, you can check out the “Fungicide Efficacy for Control of Wheat Diseases” fact sheet on the Crop Protection Network Website. Fact sheet A3878 – Fungicide Resistance Management in Corn, Soybean, and Wheat in Wisconsin has also been updated and available by CLICKING HERE.

Local data from fungicide efficacy trials in Wisconsin are also available on the Wisconsin Fungicide Test Summary Page. These trials date back to 2013 with the latest data from 2019. Be sure to scroll all the way through the documents as the wheat trials generally are listed toward the end of the documents.

Finally, don’t forget to get out and Scout, Scout, Scout to best make your in-season wheat disease management decisions!

Wisconsin Winter Wheat Disease Update – May 6, 2020

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

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

The Badger Crop Docs have started scouting wheat in south-central Wisconsin over the past few days. In general the crop needs some heat and is moving slow. However, the overall health looks good.

The mild winter of 2019/2020 was needed as a lot of the wheat was planted late and into less than ideal conditions last fall, due to the extremely wet weather. The mild winter spared stands that weren’t well established, including some of our own research plots. Most fields we have been in are still tillering.

No visible disease is present in any of the fields we have scouted. However, it will be important to keep visiting fields and scout. Also be sure to pay attention to local extension and follow our blog to keep up to speed on any developments as we move forward. The biggest disease concerns for Wisconsin wheat will be stripe rust and Fusarium head blight. You will want to be prepared to manage these diseases if they should become problematic. You can keep track of the status of these diseases nationally by visiting the Stripe Rust Ag Monitor and the Fusarium Head Blight Risk Tool.  The key to managing both diseases is to catch them before they arrive. Both of these resources can be used to help you anticipate the arrival of these diseases in your field. Continue to check back here regularly for more reports and scout, scout, scout!

Don’t let Fusarium Head Blight Keep You Down – Prepare Now to Harvest Those Scabby Wheat Fields

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Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison
Shawn P. Conley, Extension Soybean and Small Grains Agronomist, University of Wisconsin-Madison

Figure 1. FHB on some wheat heads. Note the bleached and reddened appearance of infected kernels.

Fusarium head blight (FHB) or scab has been observed at moderate to high levels in some Wisconsin winter wheat fields this season. Incidence and severity have been variable by location, susceptibility of the wheat variety, and if a fungicide was applied at or shortly after anthesis. Generally, we have observed more FHB in the southern and south-central wheat growing areas of the state, but it can be found just about everywhere we have visited this year. It is important to scout your maturing wheat crop and consider how much damage from FHB might be in a field as you prepare for harvest. While FHB can cause direct yield loss, the fungus that causes this disease can also produce deoxynivalenol (also known as DON or vomitoxin). Assessing wheat fields now can assist you in determining how much vomitoxin might be expected at harvest. However, it is possible to find high levels of vomitoxin in finished grain, even if FHB levels where low.

What does scab look like? Diseased spikelets on an infected grain head die and bleach prematurely (Fig. 2).  Healthy spikelets on the same head retain their normal green color.  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.  Often, infected kernels 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.

Figure 2. Fusarium head blight of winter wheat

Why is identifying scab important? Scab identification is important, not only because it reduces yield, but also because it reduces the quality and feeding value of grain.  In addition, the FHB fungus may produce mycotoxins, including DON or vomitoxin, that when ingested, can adversely affect livestock and human health.  The U.S. Food and Drug Administration has set maximum allowable levels of DON in feed for various animal systems, these are as follows: beef and feedlot cattle and poultry < 10ppm; Swine and all other animals < 5ppm. In addition, 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.

What should I do to prepare for wheat harvest?

  1. Scout your fields now to assess risk. Wheat is maturing rapidly. As maturity progresses it will be increasingly difficult to assess the incidence and severity of the infection. Understanding a field’s risk will help growers either field blend or avoid highly infected areas so entire loads are not rejected.
  2. DO NOT spray fungicide now. Research has demonstrated that the window of opportunity to manage FHB with fungicides is at the beginning of anthesis and only lasts about 7 days. Applications later than 7 days after the start of anthesis are not effective in controlling FHB. In addition, most fungicide labels do not allow a pre-harvest interval (PHI) suitable for a late application on wheat. Any application now would be off-label.
  3. Adjust combine settings to blow out lighter seeds and chaff. Salgado et al. 2011 indicated that adjusting a combine’s fan speed between 1,375 and 1,475 rpms and shutter opening to 90 mm (3.5 inches) resulted in the lowest discounts that would have been received at the elevator due to low test weight, % damaged kernels, and level of the mycotoxin deoxynivalenol (DON; vomitoxin) present in the harvested grain.
  4. Know your elevators inspection and dockage procedure and discount schedule (each elevator can have a different procedure and discount rate).
  5. Scabby kernels does 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.
  6. 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 (Bissonnette et al., 2018; Cowger and Arellano, 2013). If in doubt, have the straw tested for DON levels.
  7. 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.
  8. Do not store grain from fields with high levels of scab.  DON and other mycotoxins can continue to increase in stored grain.
  9. 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.
  10. For more information on Fusarium head blight 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. 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.