Head scab risk low

Most Ohio wheat growers can breathe a sigh of relief knowing that the risk for Fusarium head blight development is likely to be low this week, according to a wheat expert from Ohio State University’s College of Food, Agricultural, and Environmental Sciences.

Now that the majority of Ohio wheat is between anthesis (flowering) and early grain-fill, the threat of Fusarium head blight, also called head scab, is decreased, particularly since the region has experienced at least four rain-free days over the past week, said Pierce Paul, an Ohio State University Extension wheat specialist.

This information is gleaned using a regional online assessment tool to determine head scab development risk. The Fusarium Risk Assessment Tool available at the Fusarium Head Blight Prediction Center website, wheatscab.psu.edu, helps growers assess the risk for scab and to determine whether a fungicide application at flowering is warranted for scab control, said Paul, who is also a plant pathologist with the Ohio Agricultural Research and Development Center.

OSU Extension and OARDC are the outreach and research arms, respectively, of the college.

“While most fields are now beyond flowering, and consequently at low risk for scab, late infections still may occur,” he said. “That is especially true if conditions remain wet and humid.

“And late infections may still lead to vomitoxin contamination of the grain. But the forecasting model suggests that there will likely be low scab development this year.”

However, some late-planted fields that may be at the flowering growth stage may still be susceptible to head scab development, Paul said. Head scab is of concern for growers during flowering, which is when wheat heads are most susceptible to the scab fungus and infection is favored by warm, wet or humid conditions.

Scab is the most economically important wheat disease in Ohio because it affects wheat in multiple ways, Paul said. For example, scab can cause vomitoxin contamination of the grain, making the grain unfit for marketing and unfit for human or animal consumption.

Growers can experience a 50% or more crop loss even if they have only 10-15% of scab in their fields because more than 2 parts per million vomitoxin in the grain could cause the grain to be rejected, he said.

The scab forecasting system uses temperatures and relative humidity conditions up to flowering to calculate scab risk, helping growers determine whether there is a high, moderate or low risk for the disease, Paul said.

To use the system, growers need to select wheat type (winter) and their flowering date, which is the day when anthers are first seen sticking out of the heads. Color patterns across Ohio and neighboring states will then indicate the level of risk in the region for the flowering date selected, he said.

Red indicates a high risk, followed by yellow for moderate risk and green for low risk, Paul said. If the forecasting system indicates that the risk is moderate to high, growers should apply either Prosaro or Caramba fungicides at flowering, he said.

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