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.

 

Wisconsin Winter Wheat Disease Update – May 24

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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 in a "striped pattern" on winter wheat leaves.

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

The Wisconsin Field Crops Pathology Crew scouted winter wheat near Sharon, Wisconsin and Arlington Wisconsin yesterday. Wheat in these locations ranges from emerging flag leaf (Feekes 8) to boot stage (Feekes 10). Stripe rust (Figure 1) is increasing in incidence in the Sharon location while the overall severity (area of leaf covered by yellow spore-producing pustules) remains low. At the Arlington location, susceptible varieties in the uniform variety trial have high incidence and high severity with damage already reaching flag leaves. Wheat in surrounding fields is also beginning to show higher levels of stripe rust incidence. As previously mentioned in my May 11 post, stripe rust can be very yield limiting when it advances to the flag leaves before head emergence. Humid conditions and rainy weather will provide conditions favorable for stripe rust increase over the next week. Now is the time to scout winter wheat fields in the state and determine the incidence and severity of stripe rust in the lower canopy. By scouting the lower canopy, you can get an idea of how much risk there will be for stripe rust moving up to the flag leaf. Fungicides will be most effective when applied to wheat before stripe rust advances to the flag leaf. While scouting also note the growth stage of the wheat crop. This will be helpful in making fungicide application decisions.

To add fuel to the fire, we also need to start thinking about Fusarium head blight (FHB) or scab. Within a week or so, there will likely be fully emerged heads with anthers present on some wheat varieties in the southern and south-central region of Wisconsin. This will be a critical time to make a decision about fungicide application to control FHB. Currently, the Wheat Scab Advisor is showing little risk for FHB (Figure 2). I would urge you to pay attention to the weather over the next week. We are about to enter a warm rainy period, which will be conducive for the FHB fungus, should heads emerge and anthesis begin during this time. The Wheat Scab Advisor will likely change quickly during this period. A fungicide may be needed especially on susceptible cultivars to control FHB and reduce DON (vomitoxin) contamination. The fungicides Prosaro or Caramba have both performed well on FHB in Wisconsin. 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 where application of these effective fungicides were 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. Data from a fungicide efficacy trial to support this observation can be found by clicking here and scrolling down to pages 16 and 17. 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.

So now if you are still reading this, you are probably asking yourself “Well Damon, when should I spray fungicide now that I have two diseases to worry about and wheat is only worth $4/bu?”  My advice here will involve some leg work. I think folks need to see how much stripe rust is present this week and what growth stage the crop is at. If there is little rust present and the crop will be heading and going through anthesis in the next week or so, I would say to wait and target your fungicide application for FHB control. Both Prosaro and Caramba are rated “Excellent” in the University Small Grains Fungicide Efficacy Table.  Therefore, if you wait to spray, you are still applying a product that can protect flag leaves should stripe rust move in later. Also consider the level of resistance to stripe rust in your wheat variety. If the variety has a decent level of resistance, then the rate of spread of stripe rust up the canopy will be slow relative to susceptible varieties.

If the crop is only at the emerging flag leaf stage and you find active stripe rust in the crop, I would not wait to spray at anthesis. This could result in significant levels of stripe rust on flag leaves on susceptible or moderately susceptible varieties considering the conducive weather pattern that is forecast for Wisconsin. A strobilurin fungicide such as Headline or Aproach might be useful as a preventative application for stripe rust and these products are in a different class as Prosaro or Caramba. You should be aware that solo strobilurin fungicides do not perform well on stripe rust once the disease is established. A triazole or mixed-mode-of-action fungicide might be needed in this case, but be aware that could limit your use of Prosaro or Caramba for FHB management later in the season. Consult the fungicide labels carefully.

We have also had a couple reports of low levels of powdery mildew in a handful of fields and Septoria leaf blotch continues to cook along in the lower canopy in most fields. Stay diligent with scouting over the next couple of weeks and keep an eye on the weather. Hopefully we get enough rain to keep the crop moving along nicely and not enough to make disease worse. SCOUT, SCOUT, SCOUT!!

Wisconsin Winter Wheat Disease Update – May 11

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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

Active Stripe Rust Pustules on a Winter Wheat Leaf in Sharon, Wisconsin.

Active Stripe Rust Pustules on a Winter Wheat Leaf in Sharon, Wisconsin.

It was only a matter of time….

Today we confirmed the first observations of stripe rust in Wisconsin for 2016. Brian Mueller, Graduate Research Assistant  in the Field Crops Pathology Lab at the University of Wisconsin-Madison found active stripe rust pustules in winter wheat in both southern and south central Wisconsin. In southern Wisconsin stripe rust was found in the Wisconsin Winter Wheat variety trial located in Sharon, Wisconsin. Stripe rust was at low incidence and severity on emerging flag leaves with some lesions manifesting as chlorotic flecks and not yet active. We speculate that the epidemic initiated recently. With the humid and rainy weather over the past several days, conditions have been ripe for symptom development.

The second stripe rust confirmation was at the Arlington Agricultural Research Station in an integrated management trial for stripe rust. Again, incidence and severity were low on emerging leaves, therefore, we speculate that the epidemic has recently initiated. We have been actively looking for stripe rust as there have been numerous reports of epidemics in winter wheat in states to our south and west. Given the recent weather patterns we will likely see more stripe rust show up in the state.

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

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

Stripe rust or yellow rust of wheat is caused by the fungus Puccinia striiformis. 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. The color of the bright yellow stripe rust pustules is very different from the brick-red pustules that are common with leaf rust or stem rust. For more information on the biology of the stripe rust pathogen, and signs and symptoms, PLEASE VISIT THIS PREVIOUS POST.

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. Obviously, winter wheat is already in the ground, so you cant make a decision on resistance for the current crop, but familiarize yourself with the stripe rust resistance rating for your wheat varieties. Knowing that certain fields might be more susceptible than others will help you determine where you should be scouting first.

Fungicide applications can also be useful for controlling stripe rust when properly timed with the onset of the epidemic. Frequent scouting of fields will help you to determine when stripe rust shows up and if an application of fungicide is needed to control it. Wheat will be most susceptible to yield loss if stripe rust infects plants prior to heading. In our fields in Arlington and Sharon, this disease will be a yield limiter, especially on susceptible cultivars due to the fact that it is already becoming active on emerging flag leaves. The later that stripe rust infects, the less the impact on grain yield will be. Scouting at or near the flag-leaf emergence growth stage (Feekes 8) can help with making the decision to apply a fungicide at this critical time period.  For information on fungicides effective for controlling stripe rust, consult the recently updated Small Grains Fungicide Efficacy Table found here.

For more information about stripe rust, check out the USDA Cereal Disease Laboratory Website. They have a stripe rust informational page, which can be viewed by CLICKING HERE.

Get out there and scout!  We are approaching a critical time to make a fungicide application decision in Wisconsin.

Wisconsin Winter Wheat Disease Update – May 6

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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

Wheat

Winter Wheat Grown in Wisconsin

Winter wheat in research plots, and also adjacent production fields, was scouted in southern and south central Wisconsin during the week of May 2. Wheat at these locations ranges from Feekes 5 to Feekes 7. Wheat in general looks very good. Weather in the major wheat production area of Wisconsin has been generally dry this spring. This has resulted in very little disease pressure. We have been actively scouting for stripe rust considering reports from other states and have been unable to find any trace of rust, even in susceptible cultivars. As mentioned in a previous post, Septoria leaf blotch has been identified in low levels at some locations, however, the dry weather has lead to little progress of this disease. Powdery mildew has also been nearly nonexistent at this point.

Weather forecasts for the week of May 9 look to include some rain events. This may result in increased risk of disease onset, so this situation should be monitored carefully. We will continue to scout research plots, variety trials, and production fields for wheat diseases. As we move closer to the Feekes 8 growth stage (emerging flag leaf) the decision to spray fungicides will need to be made at that time. Remember that protecting the flag leaf from active foliar disease can be important, as that single leaf can be responsible for the majority of the grain yield of that plant. In Wisconsin, in years where leaf disease like Septoria leaf blotch or stripe rust have been active at the Feekes 8 growth stage, we have observed a significant increase in grain yield with fungicide applications at this time.  However, if conditions remain dry during this growth stage, fungicide application may not be necessary. Weather over the next several weeks will guide this decision-making process. If you are interested in learning more about effective fungicides and fungicide application timing for wheat, please visit the FUNGICIDE INFORMATION webpage or also check out fungicide efficacy trial summaries from past years on the SUMMARIES webpage.

After the Feekes 8 growth stage, the next critical growth stage for making a fungicide application decision will be at Feekes 10.5.1 growth stage or the start of anthesis. This application of fungicide will be applied to target Fusarium had blight (FHB or scab). The field Crops Pathology laboratory will continue to monitor the Wisconsin wheat disease situation. Please be sure to check back periodically for any new updates.