A major objective in the University of Illinois wheat breeding program is developing adapted scab-resistant varieties with high-yield potential, combined with all of the other traits needed for acceptance by producers and end users. An experiment studying the combination of resistant varieties and fungicides to minimize damage due to head scab, also known as Fusarium head blight, is summarized here. The primary method used for evaluating head scab resistance is a misted, inoculated field nursery where all of the wheat breeding lines and current wheat varieties are evaluated each year. Data are collected on several parameters of head scab resistance, including the percentage of Fusarium-damaged kernels and deoxynivalenol (DON) level. Deoxynivalenol is the toxin produced by the Fusarium fungus. Selection for head scab resistance each year has resulted in breeding lines with improved resistance, and some of these lines have been commercialized.
The experiment to evaluate genetic resistance and fungicides included 12 varieties differing in head scab resistance and several fungicide treatments. The results show that planting a head scab–resistant variety is very important in minimizing damage due to head scab. Prosaro and Caramba were the fungicides shown to be most effective in reducing field symptoms due to head scab, percentage of Fusarium-damaged kernels, and DON level. Under high disease pressure, combining the use of head scab–resistant varieties with the application of either Prosaro or Caramba was the best way to reduce Fusarium-damaged kernels and DON to the lowest levels.
How can wheat producers minimize the risks resulting from head scab? Begin by planting scab-resistant varieties. Varieties that are resistant or moderately resistant to head scab are available, with information on current varieties published on many state variety testing websites and in reports showing results from state variety trials. Also, plant several varieties differing in maturity. Wheat is most susceptible to head scab during and immediately following flowering, so planting varieties that flower a few days apart reduces the risk of infection; if the rainy conditions of high relative humidity that favor infection occur when one variety flowers, a second variety may escape the infection because it flowers during a period of drier weather. A head scab forecasting tool based on weather conditions is available for assessing increased risk of head scab (www.wheatscab.psu.edu). If environmental conditions increase the risk of infection, apply either Prosaro, Caramba, or Folicur at early flowering (when the first anthers are observed in the middle of the heads). Results for head scab resistance of entries in the Illinois Wheat Variety Trial are available at vt.cropsci.illinois.edu/wheat.html. For more information about suppression of head scab, wheat producers can also visit Scab Smart at www.ag.ndsu.edu/scabsmart.
Frederic L. Kolb
Professor of Plant Breeding