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Fungicide Choice and Growth Stage Timing for Wheat and Barley (06/18/15)

Winter wheat has started to flower in parts of the state and early-planted spring wheat and barley are not far behind.

Fungicide Choice and Growth Stage Timing for Wheat and Barley

Winter wheat has started to flower in parts of the state and early-planted spring wheat and barley are not far behind. With the excellent yield potential of this season’s crop and the wet weather that has moved into the state, it is time to start thinking about fungicide applications for scab suppression. Research has shown that the growth stage of the crop at the time of application can have a big impact on the level of suppression achieved with fungicides. The best time to apply fungicides for scab differ for barley and wheat (spring, winter and durum wheat are treated similarly) as described below.

Fungicide choice – The only recommended class of fungicides available for scab suppression are triazoles (ie: Caramba, Prosaro, Folicur, and tebuconazole generics). Do not use fungicides that are in the strobilurin chemistry class as these do not provide scab suppression and in some cases have shown to elevate DON (vomitoxin) levels. One final note is that fungicides are labeled for scab suppression and WILL NOT provide 100% control in conducive scab environments. An integrated approach is best; using varieties that are moderately resistant to scab, using good crop rotation practices and a properly timed fungicide application.

Fungicide timing in wheat – The optimum time to apply recommended fungicides for FHB control in wheat (winter, spring and durum) is at early flowering. Applying fungicide at this stage helps protect vulnerable florets from Fusarium damage during fertilization and early grain-filling.  The center spike in the accompanying photo is at the ideal stage for applying fungicides (Figure 1). 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. Since not all spikes emerge at the same time, fungicides are best applied when most of the main stem and first tiller spikes have reached early flowering. It may be challenging in fields of winter wheat that suffered winter-injury and therefore have a lot of variability the flowering dates of the various tillers and in some spring-planted fields with variable dates of emergence. Our recommendation is to target the spikes that are going to contribute the most to yield. In the past we have suggested that it is better to apply fungicides too early rather than too late. Recent data have suggested the opposite may be true if conditions remain favorable for scab development during early grain filling. Regardless, fungicide is better than no fungicide in conditions that favor scab development. Keep an eye on the field and the weather when deciding if and when to apply fungicides.

ppth.friskop.ransom.1.wheat flowering

Fungicide 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. Therefore, 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 optimum stage for applying fungicides to protect the glumes of barley from Fusarium graminearum infection is when the spike is fully emerged from the boot. In the accompanying photo, 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 (Figure 2).  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.

ppth.friskop.ransom.2.barley spike emerences



Andrew Friskop

Extension Plant Pathology, Cereal Crops


Joel Ransom

Extension Agronomist for Cereal Crops

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