For those fields of wheat flowering and fields of barley head-out today (May 22), the risk for head scab is moderate in the northern-most counties and in the eastern portion of central Ohio (according to the scab forecasting system at http://www.wheatscab.psu.edu). Persistent rainfall and high relative humidity over the last several days are the primary reasons for the moderate-risk prediction in these regions. However, thanks to relatively cool temperatures, and dryer conditions in some cases, the risk remains low in most other areas of the state.
Remember, the scab fungus requires moisture in the form of rainfall or high relative humidity and warm temperature to produce spores in crop residue, and for those spores to spread to wheat and barley heads, germinate, and infect. However, since infection occurs primarily between pollination and early grain-fill, scab risk is linked not only to weather conditions, but also to crop growth and development. Consequently, fields of wheat that are not yet at the flowering growth stage and fields of barley that are not yet at the heading growth stage are at low risk for head scab.
However, this picture will likely change over the next few days as it warms up, continues to rain, and more fields reach the flowering/heading growth stage. Continue to keep your eyes on the weather and the forecasting system, and be prepared to apply a fungicide. The forecasting system uses average conditions during the 15 days immediately before flowering to assess the risk of scab. Although it has been relatively cool over the last 10-12 days, with the rainfall and humidity we have experienced so far in most areas, it would only take a few (3-5) days of warm, wet conditions for the risk of scab to increase.
Wheat fields flowering and fields of barley still heading later this week and into the weekend (May 24-27) in the northern half of the state will likely be at the greatest risk for scab. Be prepared to protect them. Prosaro and Caramba are the two fungicides recommended for head scab management, and you will have a 4-5-day window from the day the crop reaches the critical growth stage (heading for barley and flowering for wheat) to make an application. Do remember to stay away from the strobilurins when the risk for scab is high as this group of fungicides has been linked to higher grain contamination with vomitoxin.
Click on the links below to see updated factsheet # PLPATH-CER-06 for more on head scab of wheat and barley and factsheet # PLPATH-CER-03 for guidelines on how to use and interpret the scab forecasting system.