Early Applications of Fungicides for Disease Control in Small Grains

Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu

Fungicide use is common in small grains and is an excellent tool to protect yields from yield robbing diseases. In the Mid-Atlantic region, our most common diseases that impact yield include powdery mildew, leaf blotch complex (Septoria and Stagonospora leaf blotch) tan spot, and rusts. Fungicides are most economical when applied to a susceptible variety and diseases are likely to affect the flag leaf, which provides the lion’s share of carbohydrates for grain fill. In a disease favorable year, fungicides applied between Feekes 8 and 10 are likely to give you the best chance of paying off.

In times where grain prices remain high, particularly in wheat, many people are experimenting with split fungicide applications. In these programs a fungicide is applied around greenup 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 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 they will not protect your plants at later stages of growth. 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 do not provide enough benefit to justify their use. Most often, foliar diseases in Mid-Atlantic do not arrive until later in the season. For this reason, early applications of fungicides may not pay in many years. In fact, holding off until heading or flowering may be of more benefit. Holding off until flowering could also help you hit two birds with one stone, so to speak, particularly if you are also concerned about head scab. However, if you planted a susceptible variety and foliar diseases appear early, you may see some benefit. If you have the time I suggest scouting your small grains every 2 weeks to help you in determining if or when a fungicide should be used on your fields. Evaluation of fungicide programs in small grains is certainly something that we need to assess in our region.

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