Wisconsin Winter Wheat Disease Update – April 15, 2015

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

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.