Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison
Shawn P. Conley, Extension Soybean and Small Grains Agronomist, University of Wisconsin-Madison
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?
- 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.
- 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.
- Know your elevators inspection and dockage procedure (each elevator can have a different procedure).
- Scabby kernels does not necessarily mean high DON levels and vice versa.
- 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).
- 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.
- Do not store grain from fields with high levels of scab. DON and other mycotoxins can continue to increase in stored grain.
- For more information on Fusarium head blight click here.
- 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.
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.