By Pierce Paul, Ohio State University Extension plant pathologist
In northern Ohio, most of the wheat fields are between Feekes growth stages 9 (full flag leaf emergence) and 10 (boot), with the odd early-planted field or field planted with an early- maturing variety beginning to head-out. In southern Ohio, fields are between Feekes 10 and early flowering (Feekes 10.5.1). For those fields of wheat at flowering and fields of barley heading-out May 20, the risk for head scab is moderate to low, according to the scab forecasting system (http://www.wheatscab.psu.edu) shown here.
However, persistent rainfall and warmer temperatures over the next few days will likely cause the risk to increase as more fields reach anthesis later this week and early next week. Remember, the scab fungus requires moisture in the form of rainfall or high relative humidity and warm temperatures to produce spores in crop residue, and for those spores to spread to wheat and barley heads, germinate, and infect. In addition, since infections occur primarily between pollination and early grain-fill, scab risk is also linked to crop development. Consequently, fields of wheat that are not yet at the flowering growth stage or fields of barley that are not yet at the heading growth stage are at low risk for head scab.
Continue to keep your eyes on crop development, the weather, and the forecasting system, and be prepared to apply a fungicide if warm, wet conditions coincide with flowering and early grain fill. 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 few days, with the frequent rainfall we have experienced so far in most areas, it will only take a few days of warm conditions for the risk of scab to increase. Prosaro, Caramba, and Miravis Ace are the most effective fungicides for head scab and vomitoxin management, and you will have a 4-6-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 strobilurin fungicides when the risk for scab is high, as this group of fungicides has been linked to higher grain contamination with vomitoxin.
Click on these links 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.