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Timing of Fungicides for Scab Control in Wheat and Barley (06/27/13)

It is hard to believe that given the cool spring and late planting of crops that one needs to address the issue of Fusarium Head Blight (FHB or Scab) control in small grains. Nevertheless, the winter wheat that established earlier in the fall is now approaching the growth stage that is most sensitive to scab infection.

Timing of Fungicides for Scab Control in Wheat and Barley

It is hard to believe that given the cool spring and late planting of crops that one needs to address the issue of Fusarium Head Blight (FHB or Scab) control in small grains. Nevertheless, the winter wheat that established earlier in the fall is now approaching the growth stage that is most sensitive to scab infection. Moreover, the earliest planted spring wheat and barley fields are beginning to head out. Environmental conditions in the next few weeks will play a significant role in whether scab will be problematic this year. The Small Grains Disease Forecasting Model is an excellent resource in determining the risk for scab development. If conditions are conduciveransom.stages_of_wheat_at_or_near_flowering for scab development, recommended fungicides can be effective in reducing scab development, particularly if applied at the appropriate stage of development. If conditions continue wet, there is a high likelihood that fungicide use will be profitable.

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 to protect vulnerable florets from Fusarium damage during fertilization and the kernel during early grain-filling.  The center spike in the accompanying photo is at the ideal stage for applying fungicides. 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. Experience has shown that it is better to apply fungicide too early rather than too late. 

Timing in barley – Flowering in barley begins just before ransom.stages_of_barley_at_or_near_spike_emergencesthe 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 malting and brewing industry is sensitive to very low levels of DON. 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. 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.  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.

Joel Ransom

Extension Agronomist for Cereal Crops

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