Fusarium head blight (scab) is a fungal disease of wheat that causes yield loss as well as grain quality issues. Arkansas has been fortunate in past years that fusarium head blight has not been a widespread problem, although parts of Northeast Arkansas had problems with this disease last year, resulting in low yields and poor quality grain. Heads or individual spikelets infected with fusarium head blight appear light pink or white (bleached) and contain shriveled scabby seed (image below). Scabby grain may contain one or more vomitoxins such as deoxynivalenol (DON) or nivalenol that the Fusarium fungus produces and may be docked or rejected at the elevator, depending on DON levels. The fungus is in every field and infection is favored by warm temperatures, rain and high relative humidity before, during, and after flowering in spring. The fungus survives on residue from previous crops and other host plants (or weeds) between wheat crops.
Planting wheat in fields behind soybean or cotton may reduce the amount of Fusarium inoculum when compared with plantings after corn, rice, grain sorghum, or certainly wheat. An integrated approach (IPM) to scab management is always preferred. Sound IPM practice prior to planting includes choosing varieties that are moderately resistant to scab rather than susceptible and/or staggering planting dates and avoiding planting multiple varieties of the same maturity group. Given the present point in the growing season, yield potential for fields, and the current rainy conditions, decisions on fungicide applications for fusarium head blight will be difficult.
Evidence suggests the best timing for scab is at flowering and applications of Prosaro at 6.5 fl oz/A or Caramba at 13.5 fl oz/A have been the most effective products to suppress scab and DON. For an estimation of the potential for scab occurrence in a particular area of the state please see the wheat scab forecasting model at http://www.wheatscab.psu.edu/. The model differs this year in that it factors in relative humidity 15 days prior to flowering and varietal resistance. In previous years, its managers indicated it was likely conservative in its prediction. After the model changes, it is likely now erring on the side of being aggressive. As with any predictive model, it is only a guide. Its value is likely limited to the regional scale rather than a field level scale. Local knowledge of practice and weather at a specific field should ultimately dictate management decisions for scab.
Special thanks to Dr. Jason Kelley for his contribution to this blog article.