New Forecasting System for Fusarium Head Blight Now Available

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

Fusarium head blight (FHB or scab) was a very damaging disease for many winter wheat growers in Wisconsin in 2014. This disease is caused by a fungus called Fusarium graminearum and infects the heads when the wheat flowers are open. Not only does the colonization of the fungus into the grain cause a reduction in kernel size and overall development, but also the fungus can produce a toxin called deoxynivalenol or vomitoxin. Vomitoxin can be extremely toxic to not only humans, but also livestock. For more information about the specific biology and management of FHB, CLICK HERE to download a fact sheet.

One of the primary methods of controlling FHB in-season is to spray fungicide. Much work has been done by university extension pathologists to determine the best time to spray fungicide to control the disease. It turns out that fungicides targeted at the anthesis (beginning flowering stage or Feekes 10.5.1) period do a good job of protecting the plants and controlling FHB. Additionally, we now know that fungicide applications up to 5 days after anthesis can also be effective in controlling FHB. Application of fungicide 7-10 days after anthesis will offer minimal control based on university research trials sponsored by the US Wheat and Barley Scab Initiative. For a list of products with efficacy on FHB, consult the 2015 Small Grains Fungicide Efficacy Table BY CLICKING HERE.

As you can tell, the timing of application of fungicide is critical for controlling FHB. You can apply the best product available, but if it goes on too early or too late, the application will be wasted. Furthermore, in some years, weather conditions will not be conducive for onset of FHB. This means that if it is really dry during the anthesis (flowering) period, infection by the FHB fungus will be low and little disease will develop. An application during dry weather at flowering will mostly be unnecessary. In order to assist growers and consultants on making fungicide application decisions to control FHB, an online FHB forecasting tool was developed. The tool can be found here: http://www.wheatscab.psu.edu.

Figure 2. FHB Forecasting System Control Panel

Figure 2. FHB Forecasting System Control Panel

In previous years, the tool has tended to under-predict FHB infection events and under-represent the amount of FHB in Wisconsin. After more data was collected and new models were assembled, a new version of the FHB forecasting system has just been released to try to improve the accuracy of the FHB forecasting system. This new 2015 release is now active and functions automatically when you visit the link above. An additional change for 2015 in the winter wheat model is the addition of susceptibility levels for the winter wheat variety you are growing. Previously, the ‘susceptibility’ choice was not available for winter wheat. Consult your seed guide to determine the level of susceptibility for your variety in order to make this input. If you can’t find this rating, then simply choose ‘susceptible. After reviewing the model and the new forecasting system at our annual wheat disease workers meeting, I think that this system is a good improvement over the other forecasting system. I believe that this system has a model with better predictive accuracy. Of course, this does not mean that it can’t fail, but should be a good tool for decision-making purposes. Remember, that your working knowledge and previous experiences are still good predictors of FHB. So even if the model is saying that risk is low and your gut says it is high, go with the ‘boots-on-the-ground’ observations and your gut.

The best time to consult the FHB forecasting system is prior to heading, and through the anthesis period. Begin consulting the model when wheat is in the boot to get a feel for the risk conditions that lead up to the flowering period in your area. Once heads have emerged and flowers are beginning to open, daily consultation of the model can assist in making that decision to spray during that critical Feekes 10.5.1 timing.

You should find the model fairly easy to use. After clicking on http://www.wheatscab.psu.edu you will be brought to the main page (Fig. 1). Enter your state (step 1) and then choose the wheat class (winter or spring) in step 2 (Fig 2). The model will update in real-time, giving you color coded risk levels. You can also choose a forecast (up to 72 hours ahead) in step 3 (Fig. 2). Additionally, your state wheat pathologist will have most likely written a commentary in the text box at the top of the page, once you have chosen your state. In Wisconsin, I try to update this weekly, especially during the critical time for controlling FHB. Remember to keep scouting and paying attention to the weather, in addition to consulting the FHB forecasting system. Here’s to an FHB-free season!

Wisconsin Winter Wheat Disease Update – April 15, 2015

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

Figure 1. Winter wheat plants in a field in Southern Wisconsin

Figure 1. Winter wheat plants in a field in Southern Wisconsin

This week I scouted winter wheat in research trials located at the Arlington Agricultural research station and also some commercial fields in southern Wisconsin. Wheat in these locations has greened up and is beginning to tiller (Fig. 1). I have observed very little winterkill on winter wheat in the fields I have looked at. Overall the winter wheat crop is looking good at these early stages with stands looking strong for the most part (Fig. 2).

Unlike the last couple of years, I have not observed any wheat diseases yet. Sometimes, Septoria leaf blotch can be observed very early in Wisconsin. We should begin to scout for diseases during these early tillering periods. If you find that Septoria leaf blotch is already present in wheat fields, then the base is set to build disease quickly if conditions are cool and wet this spring. If the spring turns to being cool and wet and a susceptible variety present, then this disease will increase and can cause enough damage to limit grain yield. To learn more about leaf blotch disease on wheat, consult THIS FACT SHEET.

Figure 2. Winter wheat stand in southern Wisconsin

Figure 2. Winter wheat stand in southern Wisconsin

Another disease to scout for at these early stages of wheat development is powdery mildew. This disease starts out as a white fluffy growth on the surface of the leaves and can progress quickly when humidity is high and temperatures fluctuate from warm days to cool nights. As the disease progresses, it can continue to cover more leaves, and the white growth may become more gray or brown in appearance. Like Septoria, if you notice early infections of powdery mildew, you have a susceptible variety planted, and conditions are conducive for the disease, then careful monitoring will be critical for making decisions about in-season control. To learn more about powdery mildew on wheat, consult THIS FACT SHEET.

Spraying fungicide when plants are very young (prior to jointing) isn’t generally recommended in Wisconsin. However, spraying to protect the flag leaf and later growth stages during heading can help preserve yield when this disease is a problem. In 2013 we conducted a fungicide trial on wheat where Septoria leaf blotch was the main disease of concern. In that trial we found that applications of fungicide at the early flag leaf emergence stage (Feekes 8) gave us good control of Septoria leaf blotch, which translated into giving us a yield increase over not spraying or spraying prior to jointing (Feekes 5). To read more about the results of this fungicide trial, you can visit THIS WEBPAGE.

In 2014, conditions were not very favorable for leaf diseases on winter wheat. However, Fusarium head scab was prevalent throughout much of Wisconsin. In our 2014 fungicide efficacy trials, we found that spraying at flag leaf emergence (Feekes 8) did not offer much yield advantage. However, spraying at anthesis (first flower; Feekes 10.5.1) did provide a significant increase in yield and significantly reduced the level of vomitoxin in grain samples. To read more about the results of the 2014 fungicide trial, you can visit THIS WEBPAGE.

The 2013 and 2014 field trials demonstrate the importance of frequent scouting of wheat to determine the right timing of fungicide application. In some years, you might need to spray at Feekes 8, in others at Feekes 10.5.1, while in some years at both timings.

In addition to the results of our field trials, you might also consult the 2015 Small Grains Fungicide Efficacy Table that was recently updated. This table offers unbiased, university research-based ratings of fungicides used on small grains. It is compiled by university research and extension pathologists from all over the country. You can find the latest table by CLICKING HERE.

It is a good idea to begin scouting now to determine what diseases are already present in wheat. Continue to watch weather forecasts as the crop matures and make plans for disease intervention measures (such as fungicide) if conducive disease conditions are present near flag leaf emergence and/or heading later this season. SCOUT, SCOUT, SCOUT!

Fusarium Head Blight and Other Winter Wheat Diseases in Wisconsin, 2014

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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: Symptoms of Fusarium head blight (scab) on a wheat head.

Figure 1: Symptoms of Fusarium head blight (scab) on a wheat head.

Winter wheat in most of Wisconsin is maturing nicely and starting to dry down in the southern portions of the state.  For most of the season, wheat diseases have been at low levels in Wisconsin.  However, certain areas of the state have been identified with high levels of Fusarium head blight (scab) in the last week.  These areas include Fond du Lac up through to Chilton and likely northward.  Growers and consultants should scout fields now to estimate the level of scab present in their fields.

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 deoxynivalenol (also known as 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 near our Fond du Lac location is maturing making it very difficult to assess the incidence and severity of the infection. Understanding a fields risk will help growers either field blend or avoid highly infected areas so entire loads are not rejected.
  2. 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.
  3. Know your elevators inspection and dockage procedure (each elevator can have a different procedure).
  4. Scabby kernels does not necessarily mean high DON levels and vice versa.
  5. DON can be present in the straw so there is concern regarding feeding or using scab infected wheat straw.  DO NOT use straw for bedding or feed from fields with high levels of scab (Cowger and Arellano, 2013).
  6. Do not save seed from a scab-infected field. Fusarium graminearum can be transmitted via seed. Infected seeds will have decreased growth and tillering capacity as well as increased risk for winterkill.
  7. Do not store grain from fields with high levels of scab.  DON and other mycotoxins can continue to increase in stored grain.
  8. For more information on Fusarium head blight click here.
  9. For More information on harvesting click here.

Other Wheat Diseases in Wisconsin

In general foliar diseases on wheat were present in low levels this year.  Some Septoria/Stagnospora leaf blotch was observed on wheat around the Arlington and Fond du Lac areas.  Severity was low at 10-20% on the lower leaves and less than 5% on the flag leaves.  Yield loss from Septoria/Stagnospora leaf blotch will be negligible this year.

Leaf rust was observed on several varieties of winter wheat throughout the wheat growing area of the state this year.  Severity on flag leaves was 10% or less and it did not typically become apparent until late in the growing season.  Yield loss from leaf rust will also be low this year.

Stripe rust was virtually non-existent this season in Wisconsin.  Only two leaves at our Arlington variety trial were found with stripe rust pustules.  Stem rust was also observed at this location in one plot, and not found at any other site that we visited this year.  Yield loss from stripe rust and stem rust will be negligible this year in Wisconsin.

Powdery mildew was not observed in any field we visited this year.

At the Fond du Lac variety trial, high levels of Cephalosporium stripe were noted on certain varieties.  This location has seen short rotations between wheat crops, likely contributing to this epidemic.  We also noted high incidence (90%) of bacterial leaf streak on several varieties at this location and the Chilton, Wisconsin location.

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.