Wheat nears vulnerable stage
May 26, 2009 10:43 AM,
By Steve Watson
Kansas State University
The Kansas wheat crop will soon be in the heading stage, which is when wheat becomes most susceptible to Fusarium head blight (FHB), or head scab, said Erick De Wolf, Kansas State University plant pathologist. FHB was a significant problem on wheat in some areas of Kansas in 2008.
Several factors are important in the development of FHB, said De Wolf, who is a wheat specialist with K-State Research and Extension. These include:
• Previous crop: The fungus that causes head scab survives in the residues of many grass crops. The fungus is also a pathogen of corn and the most severe disease often occurs when wheat is planted in fields with large amounts of corn residue left on the soil surface.
• Variety susceptibility: Most wheat varieties grown in Kansas are susceptible to the head scab, but some varieties are especially vulnerable to the disease. The varieties Overley, Jagalene, and 2137 are all highly susceptible to scab.
• Weather conditions: FHB infection of wheat takes place at flowering or during the early stages of the grain filling period. This time period clearly influences the amount of disease present. However, the weeks preceding flowering are also important. The reproduction of the fungus that causes head scab is favored by frequent rainfall and extended periods of high relative humidity. Some of the worst epidemics of scab occur when conditions are favorable for reproduction of the fungus prior to flowering followed by a few days that are conducive for infection during the flowering or early stages of grain fill.
A disease prediction system is currently available to help farmers evaluate the risk of scab in their areas. The risk of disease can change rapidly, depending on weather conditions.
"I suggest that growers access the FHB prediction Web site frequently during the next few weeks to monitor the risk of disease as the wheat approaches flowering," De Wolf said.
The prediction tool can be found at:www.wheatscab.psu.edu.
If the factors indicate a moderate to high risk of head scab, a fungicide may be needed to help suppress the disease, the plant pathologist said. Selection of an appropriate fungicide is important for head scab.
"The fungicides in the strobilurin class offer little protection and are not recommended for control of head scab. The triazole fungicides Folicur, Prosaro, Proline, and Caramba are available for use in Kansas and can help suppress disease development by 40 to 60 percent.
The fungicides must be applied to the heads to have any activity against scab, and they should be applied as close to flowering as possible. The growth stage cut-off for these fungicides is 50 percent flowering, and they have a 30-day pre-harvest interval," De Wolf said.
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