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Late-season Head Diseases of Wheat and Harvest Considerations (08/15/19)

A pending wheat harvest provides an opportunity to diagnose late-season head diseases. The most common diseases that may be observed this year at harvest are Fusarium head blight, ergot, black chaff and sooty mold.

A pending wheat harvest provides an opportunity to diagnose late-season head diseases. The most common diseases that may be observed this year at harvest are Fusarium head blight, ergot, black chaff and sooty mold. In some cases, multiple diseases may occur on one head. Here are some diagnostic tips and harvest considerations for these head diseases.

Fusarium head blight (scab)

Field Diagnosis Tips

The best time to look for scab is during the dough stages of development in wheat. Infected spikes will have premature bleaching on a portion or the entire head. When the crop approaches maturity, there are a few things that can be observed on Fusarium infected heads. Signs of the pathogen are the best indicator of scab and include pink to orange colored fungal growth (Figure 1A) on infected spikelets. Infected spikelets will often have kernels that are shriveled, light and appear lifeless (Figures 1B).

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Harvest Considerations

In severe FHB-stricken wheat fields, adjusting the combine fan speed may help blow out additional lightweight severely infected kernels. However, if there was a late infection by the Fusarium pathogen, the kernel’s weight may not be impacted, but deoxynivalenol/vomitoxin (DON/VOM) can still be a concern. If you suspect FHB damage, do not mix the grain from fields that were planted at different times or with different varieties until they have been tested for DON levels as these practices can result in large differences in DON. For more information on handling small grains with DON/VOM please review (https://www.ag.ndsu.edu/publications/crops/plant-disease-management-deoxynivalenol-don-in-small-grains-1).

Ergot

Field Diagnosis Tips

Last season presented some problems with ergot in spring wheat and rye. Although we have received some reports of ergot, it has been localized near field edges or near grassy weeds in field margins. The most diagnostic sign of the ergot pathogen are ergot bodies. Ergot bodies (sclerotia) are black-purple, hard, irregular shaped, and are noticed is a mature wheat field (Figure 2).

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Harvest Considerations

Now is a great time to look for ergot incidence in field. Most problems with ergot will be greater along field margins. If severe, mark the most impacted areas and harvest separately. Again, keeping sound grain separated from contaminated grain will help avoid problems at the point of sale. Ergot bodies tend to resemble the weight of a wheat kernel and are likely not impacted by combine fan speed. For more information on ergot, please review (https://www.ag.ndsu.edu/publications/crops/ergot-in-small-grains/pp1904.pdf)

Black Chaff

Field Diagnosis Tips

Black chaff is simply the bacterial leaf streak pathogen that has infected a wheat spike. Infected spikes will appear discolored and have discolorations on glumes and awns. Discolorations associated with black chaff will not “rub off” and will be embedded in leaf tissue. Fields with high levels of bacterial leaf streak may have black chaff symptoms.

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Harvest Considerations

The pathogen responsible for bacterial leaf streak and black chaff can survive on seed, but survival efficiency is low. More research is needed document the survival of the bacterium in seed storage conditions.

 

Sooty Mold

Field Diagnosis Tips

Sooty mold is the name given to saprophytic fungi that colonize dead tissue. On wheat spikes that have prematurely died, saprophytic fungi, often black to green in color, will colonize the spikes giving them a dirty appearance (Figure 4).

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Harvest Considerations

Sooty mold may contribute to a dirty harvest and rarely impacts seed quality.

 

 

Andrew Friskop

Extension Plant Pathology, Cereal Crops

 

Joel Ransom

Extension Agronomist, Small Grains and Corn

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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