Editor’s Note: For tables see full article at the source link at the bottom of the page.
Wheat leaf diseases such as powdery mildew, Septoria leaf spot and stripe rust are prevalent in some fields this season. Many farmers are asking if a fungicide application should be made prior to the typical application for Fusarium head blight (head scab) management at flowering (anthesis, Feekes growth stage 10.5.1, Zadoks 60).
There are a few key points to consider when making fungicide decisions in wheat, since multiple fungicide applications are rarely profitable in wheat. The following decision tree outlines when and what actions should be taken by growth stage.
The first rule is to scout, scout, scout! Knowing the wheat growth stage, what disease is present, variety susceptibility to diseases and where diseases are in the plant canopy is essential to making the most profitable disease management decisions.
The stripe rust pressure has been unprecedented in the Great Lakes region this season. The extended cool spring along with significant overwintering of stripe rust in the southern U.S. has resulted in a “perfect storm” for disease development.
Rusts tend to move quickly, with a 10-day window from infection to reproduction. At full flag leaf emergence (Feekes 9; Zadoks 39), if disease is only present two leaves below the flag leaf (F-2), then continue to monitor. If disease is present on the leaf below the flag leaf (F-1), applying a fungicide will provide the most protection.
Once leaf damage has occurred, rescue treatments may only halt or slow disease, but won’t rescue dead leaves. Be aware that if a fungicide is applied to fully emerged flag leaves, well in advance of head emergence, then an additional fungicide application will be required to control Fusarium head blight at the beginning of flowering.
However, be mindful of the current growth stage. Once wheat plants move into the boot stage (Feekes 10; Zadoks 45), the application of products containing a strobilurin fungicide may actually increase the amount of mycotoxin (DON/vomitoxin) in the grain.
If no significant disease pressure is present or active on fully emerged flag leaves or one leaf below (F-1), then waiting for an application for head scab management makes sense. A fungicide application during flowering will work two-fold.
First, it will provide some reduction in head scab and mycotoxin suppression. Second, it will also provide protection of the flag leaf. Susceptible to moderately susceptible varieties will be at greatest risk of head scab and DON accumulation.
Other risk factors should be considered such as history of disease, previous crop and current weather conditions.
The Fusarium Risk Assessment Tool is available to give a daily risk assessment for specific locales. The model is correct about 75 percent of the time, but Michigan State University Extension encourages growers to consider their own experience and that of local consultants.
Remember that the beginning of flowering is defined as 50 percent or more of the heads in a field with flowers present.
The window for fungicide application for head scab was recently found to be optimal from the beginning of flowering (anthesis) until six days after the beginning of flowering (anthesis), with best management achieved with an application four days after the beginning of flowering.
Fungicide efficacy for control of wheat diseases
The multi-state North Central Regional Committee on Management of Small Grain Diseases (NCERA-184) has developed the following information on fungicide efficacy for control of certain foliar diseases of wheat in the U.S. (revised March 30, 2016).
Efficacy ratings for each fungicide listed were determined by field testing over multiple years and locations. Efficacy is determined by direct comparisons among products in field tests. The products are used in a manner consistent with label instructions. This table includes most widely marketed products. It is not intended to be a list of all labeled fungicide products.