Wisconsin Winter Wheat Disease Update – April 21, 2017

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Two small Stripe rust pustules on a winter wheat leaf.

Brian Mueller, Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin-Madison

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

The Wisconsin Field Crops Pathology crew has continued to scout wheat in various locations around the state of Wisconsin. Wheat in the southern part of the state is near or at jointing. Wheat in the central zone is also near jointing.

We have now confirmed stripe rust in a production winter wheat field near Arlington Wisconsin (April 20, 2017). The variety is Pro Seed 420 which is known to be susceptible to stripe rust. We suspect that stripe rust has overwintered in this location, in addition to the Sharon Wisconsin location that we reported several weeks ago. We have also received a report of stripe rust from Kenosha Co.

In all cases where stripe rust has been found, it is at low incidence and severity. However, the weather is becoming conducive for the stripe rust pathogen, so these areas of active rust should be monitored closely so that an informed management decision can be made. Many are considering a tank-mix of fungicide with their herbicide application. However, be aware that this application will only be effective for 2-3 weeks at most. We have found that when it comes to application of fungicide for stripe rust control, applications that coincide with the introduction of stripe rust that also protect the flag leaf, are most beneficial on winter wheat in Wisconsin. This has been investigated and reported by our laboratory and presented at the Wisconsin Agribusiness Classics.  You can find that report here.

At this point in the season, growers and consultants should continue to scout carefully for stripe rust. Also, consider the susceptibility rating of your wheat varieties. In fields where stripe rust is active and you have a susceptible variety, careful monitoring will be required and earlier spraying necessary. In fields with no confirmed rust and resistant varieties, continued monitoring of the situation will be necessary. Fungicide application should be saved until as close to flag leaf emergence as you feel comfortable waiting. You can find efficacy ratings of various fungicide products against stripe rust here.

Get out and scout, scout scout!!

2017 Field Crop Fungicide Efficacy Tables Now Posted

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

Northern Corn Leaf Blight symptoms on a corn leaf.

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

Stripe Rust Found to be Present and Already Active in Wisconsin Winter Wheat

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Brian Mueller, Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin-Madison

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

Figure 1. Urediniospores of the stripe rust fungus. Red arrow indicates a germinating, viable spore.

On March 29, 2017 the Field Crops Pathology Team observed the first signs of stripe rust in Wisconsin for the 2017 field season. Plots were located in the Wisconsin Winter Wheat variety trial in Sharon, Wisconsin. A sample was brought back to the Field Crops Pathology lab and placed on water agar to test for spore viability. The red arrow in figure 1 points toward a germ tube extending from the base of a urediniospore, indicating a viable spore. Very low levels of disease incidence and severity were detected in the plots scouted (Fig. 2 and 3). It is speculated that the pathogen that causes stripe rust overwintered on wheat leaves that remained green through the winter of 2016/2017. These same plots were scouted and confirmed to have active stripe rust infection this past fall (Fall 2016). However, application of fungicide was not recommended because stripe rust typically does not overwinter in the northern U.S. To our knowledge this is the first time that overwintering of the stripe rust fungus has been observed in Wisconsin winter wheat fields and is likely due to the mild winter season.

Figure 2. A single pustule of the strip rust fungus on a wheat leaf.

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 as seen in Figure 2. Disease is favored by prolonged periods of rain (or dew), high relative humidity, and cool temperatures ranging from 50 to 60 ºF. For more information visit the USDA Cereal Disease Lab website.

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, 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.

Figure 3. Low incidence and severity of stripe rust on winter wheat.

While we typically don’t recommend an application of fungicide at the Feekes 5 growth stage, an application might be necessary this season if you find stripe rust in your wheat stand. This fungicide application could be tank-mixed with your last herbicide application. You should scout prior to this treatment, as it will only be necessary if active rust is observed. Products labeled for control of stripe rust can be found in publication A3646 – Pest Management in Wisconsin Field Crops. Many fungicides are labeled with excellent efficacy on stripe rust. So, find a product rated excellent, that also fits your pocketbook. Finally, remember to stick with labeled rates. Get out there and scout!

2016 Wisconsin Field Crops Pathology Fungicide Tests Summary Now Available

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

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

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

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

2016 Wisconsin Pest Management Update Tour Slides Now Live!

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

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

Start Managing Stripe Rust of Winter Wheat in 2017 At Planting

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Brian Mueller, Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin-Madison

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

Figure 1. Stripe rust in a "striped pattern" on winter wheat leaves.

Figure 1. Stripe rust in a “striped pattern” on winter wheat leaves.

The 2016 Wisconsin winter wheat field season was reasonably successful with very high yields and low levels of Fusarium head blight throughout much of the state. The major disease concern this season was stripe rust. Some cultivars were hit very hard by this disease. Since 2000, stripe rust has become an increasing concern on winter wheat in the Midwest. In Wisconsin over the last four seasons, we have observed consistent stripe rust pressure on some varieties throughout the wheat production area of the state. Because of the consistent occurrence of stripe rust over the last few seasons, it is reasonable to expect continued pressure from this disease in 2017.

Stripe rust is caused by the fungus Puccninia striiformis. This fungus is in the same group of organisms that cause other rust diseases of wheat such as leaf rust and also the famed disease stem rust, which put the importance of wheat breeding on the map. Stripe rust can be identified readily by the bright yellow pustules that typically occur in a striped pattern on the surface of the wheat leaf (Fig. 1).

The stripe rust pathogen survives on wheat debris as spores or mycelium (fungal threads) in areas where the temperatures don’t get above 90 F or below 20 F. It is thought that stripe rust cannot overwinter in the far northern areas of the U.S. such as Wisconsin. Little is know if the stripe rust fungus can survive the summers in Wisconsin, once the wheat crop has been harvested. We are working on trying to understand the epidemiology of this pathogen better.

Because survival of the fungus might be limited in Wisconsin, the stripe rust pathogen most likely has to be windblown from the southern states into our wheat production area. This is why we need to pay close attention to stripe rust reports from the southern states.

Stripe Rust Management

Management of stripe rust includes using resistant cultivars and applying fungicide, along with using some cultural practices such as avoiding excessive fertilizer applications and eliminating volunteer wheat plants. Your job in managing stripe rust really begins now before planting. Take time to study the 2016 Wisconsin Winter Wheat Performance Trial report. These 2016 trial results include ratings for stripe rust. Locate the trial that was situated closest to you and look for a wheat variety that yielded well and had little stripe rust.

Figure 2. Wheat Stripe Rust Severity and Yield Loss Relationship Across Four Wisconsin Locations in 2016

Figure 2. Wheat Stripe Rust Severity and Yield Loss Relationship Across Four Wisconsin Locations in 2016

In 2016, stripe rust caused a significant amount of yield reduction in the state. Across all varieties and variety testing locations in the state, the average yield potential was 130 bu/a. This was an excellent yield potential, however stripe rust caused a significant reduction in yield on susceptible varieties. In 2016 approximately 5.4 bu/a were lost for every 10% increase in flag leaf stripe rust severity (area of the flag leaf covered in rust) in Wisconsin (Fig. 2). This is a substantial yield reduction in these trials. It should be noted that no fungicide was used, thus, some wheat varieties have excellent resistance and yield potential and should be top choices to consider for planting in 2017.

In addition to choosing a resistant winter wheat variety, you can start making some decisions on what your fungicide program might look like. There are several effective fungicides for stripe rust. To find a product with an excellent efficacy rating, consult the Small Grains Fungicide Efficacy Table. Once you have sourced a suitable fungicide for your operation, timing of application of that product becomes the most important decision. We conducted an integrated management trial for stripe rust of winter wheat in 2016. In that trial we applied fungicides at three growth stage timings (jointing, flag leaf emergence, boot stage) and compared them to a non-treated control or full-season fungicide protection (not a recommended program, but was used as a positive control or best-case scenario). We applied fungicide at these growth stages on wheat varieties rated as resistant (Pro Seed 380), moderately susceptible (Kaskaskia), and susceptible (Pro Seed 420).

Figure 3. Mean Relative Stripe Rust Incidence on Three Winter Wheat Varieties Treated with Fungicide at Three Growth Stages Compared to Not-treating or Treating with Fungicide Full- Season

Figure 3. Mean Relative Stripe Rust Incidence on Three Winter Wheat Varieties Treated with Fungicide at Three Growth Stages Compared to Not-treating or Treating with Fungicide Full- Season

Figure 3 shows the mean relative stripe rust incidence (number of plants per plot with stripe rust) at each fungicide application timing on the three varieties. You will note that Pro Seed 380 was resistant enough that very little stripe rust occurred even in the non-treated control. Fungicide application on this variety resulted in no difference because of the low incidence. For Kaskaskia and Pro seed 420, however, the flag leaf and boot fungicide application timings offered suitable reductions in stripe rust incidence. The reason for this response is that stripe rust was first observed around the emerging flag leaf growth stage. Thus, fungicide application timing near the appearance of the disease offered excellent control. Figure 4 shows the mean yield response for for these same treatments. The trend followed that of the incidence data. No significant yield response was observed for Pro Seed 380 for any of the fungicide application timings, as it was highly resistant to stripe rust. Kaskaskia and Pro Seed 420 responded to the fungicide application timing with the best single application being either the flag leaf or boot application timing.

Summary

Figure 4. Yield of Three Winter Wheat Varieties Treated with Fungicide at Three Growth Stages Compared to Not-treating or Treating with Fungicide Full-Season

Figure 4. Yield of Three Winter Wheat Varieties Treated with Fungicide at Three Growth Stages Compared to Not-treating or Treating with Fungicide Full-Season

To best manage stripe rust on winter wheat in 2017, start now by choosing the most resistant, highest-yielding variety appropriate for your location based on the 2016 Wisconsin Winter Wheat Performance Trial report. Once you have chosen your variety, choose a fungicide that will best fit your operation, with a high level of efficacy based on the Small Grains Fungicide Efficacy Table. Next spring begin scouting your wheat crop frequently. Don’t use your fungicide application until you first see stripe rust. This will likely be closer to flag leaf emergence or the boot stage in Wisconsin. Don’t forget about other diseases like Fusarium head blight (FHB). You might have to treat twice with fungicide if the weather is conducive next season for FHB and you have to spray early for stripe rust. Remember that fungicides effectively protect wheat plants for around 14 days. To learn more about managing FHB in 2017, CLICK HERE.

Wisconsin Winter Wheat Disease Update – June 29

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

Brian D. Mueller, Graduate Research Assistant, University of Wisconsin-Madison

Winter Wheat Grown in Wisconsin

Winter Wheat Grown in Wisconsin

This will likely be the last winter wheat disease update for 2016, as the University of Wisconsin Field Crops Pathology team has nearly finished winter wheat disease ratings for 2016. In our travels this season we have determined that the major disease of concern was stripe rust. We were able to find stripe rust in every field we visited this season. In the variety trials throughout the state, stripe rust hit some varieties very hard, causing significant damage and early defoliation. Other varieties did fair well, so genetic resistance was obviously a big player for us this season. In production fields that did not receive an application of fungicide, stripe rust was often moderate to severe. Fields with resistant varieties and/or that received a well-timed fungicide had low levels of stripe rust and will yield well.

Unlike 2015, Fusarium head blight (FHB or scab) has been relatively minimal. In the southern and eastern wheat production areas of the state we could find some low levels of FHB, however, severity is fairly minimal. This is likely due to the fact that the weather was very hot and mostly dry during the anthesis period in this part of the state. Further to the north and closer to Lake Michigan, we have found higher levels of FHB. In a production field near Marshfield, in central Wisconsin, FHB levels were significantly higher than observed in other parts of the state. Incidence was around 25-30% with severity averaging 15-20%. These higher levels of FHB likely resulted from more favorable weather for the FHB fungus during anthesis in this part of the state. For more information about how to handle FHB as we approach harvest CLICK HERE.

Septoria leaf blotch was present in low levels in some fields. However it won’t be a substantial yield-reducer in 2016. Powdery mildew was nearly non-existent in the state for the fourth season straight.

Fusarium Head Blight and Wisconsin Wheat Harvest in 2016

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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. Fusarium head blight on a wheat head

Figure 1. Fusarium head blight on a wheat head

Fusarium head blight (FHB) or scab has been relatively low in most Wisconsin winter wheat fields this season. Occasionally we have run across a field with somewhat higher levels of FHB; however, compared to the 2015 crop, we suspect that the 2016 winter wheat crop should have much less FHB. With that said, it is still 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.

What does scab look like? Diseased spikelets on an infected grain head die and bleach prematurely (Fig. 1).  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.

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.

What should I do to prepare for wheat harvest?

  1. Scout your fields now to assess risk. Wheat is beginning to mature. As maturity progresses over the next couple of weeks, 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 (each elevator can have a different procedure).

  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 (Fig. 2). However, when the finished grain was tested for DON, significant levels were identified for all treatments (Fig. 3). 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 (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. For more information on Fusarium head blight click here.

References

Cowger, C., and Arellano, C. 2013. Fusarium graminearum infection and deoxynivalenol concentrations during development of wheat spikes. Phytopathology 103:460-471.

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 – June 16

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

Brian D. Mueller, Graduate Research Assistant, University of Wisconsin-Madison

Figure 1. Stripe rust spores on a wheat leaf, being collected for research.

Figure 1. Stripe rust spores on a wheat leaf, being collected for research.

The University of Wisconsin Field Crops Pathology team has completed leaf disease ratings at all Wisconsin winter wheat variety trials this week. We will begin rating for Fusarium head blight (FHB) damage in these same trials next week. We have also scouted wheat in production fields in various areas. Most wheat has completed anthesis and is filling grain. No FHB has been observed up to this point. However, stripe rust is pretty serious in most locations we have been (Figure 1). On susceptible varieties that haven’t been sprayed with a fungicide, we have observed 100% incidence with average severity on flag leaves ranging between 30 and 90%! We even have our token “Yellow Jeans” picture to demonstrate how severe stripe rust is in some fields (Figure 2). While there are many cases of severe stripe rust, we have observed some varieties to be very resistant. Little or no rust observed (Figure 3). I think there will be a wide range in yields of winter wheat this year in Wisconsin, based on stripe rust severity. Those who did not spray fungicide and have susceptibility will see significant yield losses and reduced test weight.

Figure 2. Stripe rust spore on denim jeans

Figure 2. Stripe rust spore on denim jeans

We have seen very few other foliar diseases on wheat during our travels. Leaf blotch diseases are present in some fields in the lower canopy, but in many cases, stripe rust is out-competing those diseases. We found powdery mildew in one isolated location in one field we have been in. We suspect that we will find some FHB over the next several weeks as portions of the state had favorable weather for the FHB fungus during anthesis. We will continue to monitor this situation and alert you to what we find.

Figure 3. A stripe rust susceptible winter wheat variety on the left and a resistant winter wheat variety on the right. Note the yellow leaves on the variety on the left.

Figure 3. A stripe rust susceptible winter wheat variety on the left and a resistant winter wheat variety on the right. Note the yellow leaves on the variety on the left.

Finally, I want to note that fungicide applications should not be made after the anthesis period. Most fungicide will no longer be effective on these diseases once established. Also, the pre-harvest intervals on these products will not allow application after the anthesis period.

Wisconsin Winter Wheat Disease Update – June 1

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

Brian D. Mueller, Graduate Research Assistant, University of Wisconsin-Madison

Figure 1. FHB Advisor June 1. 2016

Figure 1. FHB Advisor June 1. 2016

Despite the warm and rainy pattern that much of Wisconsin has been subjected to over the last week or so, the wheat FHB (scab) advisor  is predicting low risk of FHB over much of the state (Fig. 1). Just a narrow band of moderate to high risk exists very close to the Lake Michigan shore. Extending the advisor out 72 hours increases risk for FHB slightly for susceptible cultivars, but leaves the majority of the state still at low risk.

In addition to FHB risk, there is a relatively high incidence of stripe rust in many fields that we have scouted. The Wisconsin Field Crops Pathology Crew scouted Winter Wheat Variety trials and commercial fields near Chilton and Fond du Lac on May 27th. At both locations, wheat ranged from boot stage to heading. Anthesis will occur sometime this week or is occurring as we speak in many of the varieties.

The primary disease at the Fond du Lac location was stripe rust. Incidence (less than 10% across varieties) and severity (less than 5% on F1 or F2 leaves) was generally low in most varieties. One variety in the small plot variety trial had stripe rust present on very old tillers. In fact, stripe rust had been active for a while as telia (pathogen structure) were forming. I suspect that stripe rust may have over-wintered on this variety at Fond du Lac considering our mild winter.

At the Chilton location, stripe rust incidence was much higher (25-30%) however, severity was generally low (less than 5% on F1 leaves). However, there were several hot spots of stripe rust present in the variety trial and also commercial wheat surrounding the trial. Growers will need to watch this situation carefully. I fear that stripe rust will be increasing dramatically this week with our rainy and humid weather.

If a fungicide has not been applied yet, stripe rust is present, and anthesis has begun this week, a fungicide should be considered to control FHB and stripe rust together. The fungicides Prosaro or Caramba have both performed well on FHB in Wisconsin and are rated “Excellent” for stripe rust. Timing of application of these products is critical. I would urge you to wait until anthesis has begun in your field before applying. We have observed poor control of FHB where application of these effective fungicides was made before anthesis. In fact, we have observed improved control of FHB and lower levels of DON in finished grain where fungicide application was delayed 4-5 days after the beginning of anthesis, compared to applications at the start of anthesis. Also, remember that application of fungicides should be made no later than 6-7 days after the start of anthesis. After this time, fungicide efficacy on FHB is much reduced.