Head scab could be result of warm, wet conditions over past few weeks

WOOSTER, Ohio – With wheat flowering throughout Ohio, now is the time for the potential for head scab – a disease that affects the crop during wet, warm conditions. Wheat growers can refer to the Fusarium Head Blight Risk Assessment Tool (http://www.wheatscab.psu.edu) to evaluate the risk of head scab development on wheat in their county.

According to the site, for wheat flowering the beginning of this week, the risk of scab is moderate for most of the state.

Calculate risk

“The tool uses weather conditions seven days leading up to flowering to calculate risk. In general, prolonged periods of warm and wet conditions increase the risk of scab,” said Pierce Paul, an Ohio State University Extension plant pathologist and wheat specialist.

“Barring late-planted fields in central Ohio and early-planted fields in the north, most fields in central Ohio and especially southern Ohio flowered before this wave of moderate to high risk came through, and as such, should have escaped a major scab epidemic.

“In spite of the frequent rainfall during the early part of our flowering season, conditions were cool, so fields in southern Ohio likely escaped major scab problems because of cool temperatures. Similarly, fields flowering later this week in northern Ohio and late-planted fields in central Ohio will likely escape scab because of dry conditions, even though temperatures are predicted to be in the 80s for most of the next 5 days.”

Flowering

Fields that flowered between May 21 and May 24 that received frequent rainfall and warm temperatures during the seven days leading up to flowering would be at greatest risk, said Paul.

“If it stays warm, but stops raining as is predicted for the rest of this week, the risk of head scab will likely decrease in the northernmost counties where the wheat will be flowering this week,” said Paul, who also holds an appointment with the Ohio Agricultural Research and Development Center. “As wheat continues to flower, growers should check the risk tool frequently.”

In addition to using the Fusarium Head Blight Risk Assessment Tool to evaluate the risk of head scab, growers have a few other tools at their disposal.

Tools to use

One is Scab Alert (http://www.scabusa.org), launched by the U.S. Wheat and Barlety Initiative. Scab Alert allows producers, crop consultants, grain processors and others in the wheat industry to receive up-to-date head scab information via cell phone and/or e-mail.

Another tool to help manage head scab is Scab Smart (http://www.scabsmart.org). Provided by the U.S. Wheat and Barley Initiative and the U.S. Department of Agriculture Agricultural Research Service, the service provides best management practices for scab using fungicides (timing and application technology), variety resistance (based on data from wheat performance trials), crop rotation, residue management, planting date, and harvest practices.

“Fungicides for scab management are most effective when applied at flowering. Some level of scab suppression will occur with applications done two to three days before or after flowering, but efficacy drops considerably as you move away from the actual day the crop flowers,” said Paul.

Fungicides

Of the available fungicides, Proline, Prosaro and Caramba are the most effective.

“Folicur provides some suppression, but is not as effective as the other three produces. A tank mix of Folicur and Proline (3+3) provides control comparable to that of Prosaro,” said Paul. “Strobilurin-based fungicides are not recommended for scab management.”

Disease development

Head scab, if it develops, isn’t the only thing that could impact wheat yields right now. Recent cooler temperatures caused the wheat heads in some fields and some varieties to emerge more slowly, preventing them from completely emerging. The result could be yield reductions.

“Relatively warm temperatures allow the heads to emerge quickly and easily from the leaf sheath, whereas cold temperatures slow down this process and may even prevent the heads from emerging completely, leaving them trapped by the tip,” said Paul. “Fields planted with varieties that are more sensitive to cold temperatures were the ones most affected.”

Paul said that farmers are reporting 20 percent to 50 percent of the wheat head being trapped in the boot.

“Head being trapped in the boot is not an unusual occurrence, but the high numbers of wheat heads getting trapped is alarming,” said Paul.

“Some producers are concerned, but the situation does not necessarily mean that their varieties will automatically suffer a yield reduction.” Paul said yield would only be affected if the heads are distorted to the point of blocking or stopping the flow of water and nutrients to the spikelets.

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