Best Stage For Applying Fungicides For Scab Control In Wheat, Barley

Main stem and first tiller spike development is the key in wheat; spike emergence from the boot is the trigger in barley.

Published on: Jun 7, 2013

The optimum time to apply recommended fungicides for fusarium head blight control in winter wheat, spring wheat and durum is at early flowering, says Joel Ransom, North Dakota State University Extension agronomist.

"Applying fungicide at this stage helps to protect vulnerable florets from Fusarium damage during fertilization and early grain-filling," he says.

The center spike in the photo of wheat heads below is at the ideal stage for applying fungicide. The spike on the left has emerged from the boot, but has not yet started to flower (there are no visible anthers extruded from the glumes and will likely be at the optimum stage in about two days.) The spike on the right is past the optimum stage. The anthers are bleached and dried unlike the turgid, yellow anthers in the center spike. The period between head emergence and flowering is usually about three days.

Stages of barley at or near flowering.
Stages of barley at or near flowering.

"Since not all spikes emerge at the same time, I recommend applying fungicides when most of the main stem and first tiller spikes have reached early flowering. Furthermore, experience has shown that it is better to apply fungicide too early rather than too late," he says.

Timing in barley
Flowering in barley begins just before the spike emerges from the boot, so barley florets are not overly susceptible to scab infection, Ransom says. Scab infections do not generally impact yield in barley. The scab fungus, however, is able to infect the glumes of barley and produce DON which impacts its market value, particularly if it is being sold for malt. The malting and brewing industry is sensitive to very low levels of DON.

Stages of wheat at or near flowering
Stages of wheat at or near flowering

The optimum stage for applying fungicides to protect the glumes of barley from FHB infection is when the spike is fully emerged from the boot, Ransom says.

In the photo of barley heads below, the spike third from the left demonstrates the optimum stage for treating barley with fungicides, with those further to the left too early and the one on the right too late. With barley the appearance of the first spikelet from the boot is a good indication that the best stage for spraying is only a few days away.

Source: NDSU