NDSU Extension - Mercer County


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Fungicide Choice and Growth Stage Timing for Wheat and Barley

fungicide, wheat, barley, scab suppression, vomitoxin

Submitted by Craig Askim, Extension Agent, Agriculture and Natural Resources

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. 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.

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 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 with 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 has 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.

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.

Source: Andrew Friskop – NDSU Plant Pathologist

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