The drought conditions we have been experiencing across most of the Prairies has resulted in variability in growth stage of both wheat and barley, as well as other crops. This has made it particularly challenging to determine if the field is at the proper growth stage for the application of fungicide. Targeting the application to a specific growth stage is critical to prevent economic losses because of plant disease. Protecting for foliar diseases only is usually focused on applying a fungicide when the flag leaf has fully emerged. The timing of a fungicide to manage Fusarium head blight is the initiation of flowering. Recently, research has shown that timing of fungicides for Fusarium head blight, initiation of flowering, will also provide control of late season foliar diseases and provide the best opportunity for the maximum yield benefit over untreated.

Cereal fungicide timing

If there is variability in growth stage of the crop within a field, what stage should be used to determine when to apply a fungicide?

It is challenging to decide the growth stage of the crop when there is variable plant maturity in the field. In particular, when timing a fungicide application that is to be applied at heading. Not all heads will emerge at the same time and when the crop has been impacted by drought or variable emergence it can result in significant variation in growth stage. Focusing on the heads that will contribute the most to yield and basing the application timing on those plants is the best recommendation. It is suggested that under these conditions, when approximately 75% of the heads are fully emerged and 50% of the heads on the main stem are in flower a fungicide application should be made.

What is the time window for application if the focus is Fusarium head blight?

In addition to variability of plant growth, timing is critical, and the spray window is short, approximately only 7 days. Fusarium head blight spores infect from the start of flowering to the soft dough stage, so the application window for wheat must be targeted to when most of the heads have 100% emerged from the boot and at least 50% of the heads are flowering. In barley, since it begins flowering in the boot stage the application window is when the heads are 70%-100% emerged from the boot (at the beginning of head emergence).

How should the growth stage of the field be determined versus the growth stage of a single plant?

It is important to take a random, non-biased, sample of the plants in the field to determine the growth stage; however, the sample plant should be representative of the plants in the area from which the plant is chosen. When scouting, it is recommended that most prone regions to disease be checked, such as low areas and along shelter belts as these areas can be the first to become infected and give an indication of the diseases that are present. A suggested sampling protocol can be found at this site. If the field appears to be divided into two or more distinct growth stages, it may be advisable to consider the field as two or more separate fields to determine the application timing. If only one application is to be made, the decision should be based on the stage of the majority of the plants in the field.