Fungicide Use In Wheat

Nathan Kleczewski Ph.D
Extension Specialist- Plant Pathology
Department of Plant and Soil Sciences

Fungicide use is common in small grains and is an excellent tool to protect yields from yield robbing diseases.  In Del-Ma, our most common diseases that impact yield include powdery mildew, leaf blotch complex (Septoria and Stagonospora leaf blotch), tan spot, and rusts.  Often, fungicides applied to a susceptible variety when diseases approach the flag leaf will give you the most consistent yield protection.  This is because the flag leaf provides the lions share of carbohydrates for grain fill.  Recommended timings for protection of the flag leaf is between Feekes 8 and 10.

In times where wheat prices remain high, many people are experimenting with split fungicide applications.  In these programs a fungicide is applied around green-up or jointing with an herbicide, and often a cheap triazole is used.  This early application is then followed by a second fungicide application at the Feekes 8-10 timing.  Others may apply a more expensive fungicide at a reduced rate (for example, 3 oz when 6 oz is the lowest labeled rate) and come back with a full rate fungicide application later in the season.  The idea behind the early treatments is to keep the developing plant clean until the flag leaf emerges, thereby increasing yield potential.  Remember that fungicides give you roughly 14 days of full protection and another 7 days of partial protection, so green-up or jointing applications will not protect the plant from late season diseases.  Additional drawbacks include the additional cost of the fungicide and the additional exposure of the pathogen population to a particular fungicide mode of action.  Increased exposure to a particular mode of action increases the risk of resistance development in some fungal pathogens.  The use of reduced fungicide rates (below label rate) further increases resistance risk.  Powdery mildew is a great example of a pathogen that can easily develop fungicide resistance.

Split applications such as those described have proven useful in some states, particularly in areas where spring wheat is planted or where foliar diseases come in hard and early in the season.  However, in many situations early applications may not be needed.  Often, foliar diseases in Del-Ma do not arrive until later in the season.  Thus, a single spray at Feekes 8-10 may be all that is needed in many disease favorable growing seasons.  The exception is powdery mildew, which has caused significant levels of disease on susceptible varieties in disease favorable years.  If you know your variety has a chink in its powdery mildew armor, then an early season application may provide some benefit.

There is no easy answer with fungicide use in Del-Ma wheat.  The impact of a disease on yield is dependent on the variety, the environment, and the pathogen.  The best way to make informed spray decisions is to know your variety, pay attention to the weather, and scout your fields.  If you have the time I suggest scouting your small grains every 1-2 weeks to help you determine if or when a fungicide should be used on your fields.

Source : udel.edu