Wheat harvest will soon be upon us in Indiana. Fusarium head blight (FHB) or scab is one of the most important diseases of wheat and most challenging to prevent. In addition, FHB infection can cause the production of a mycotoxin called deoxynivalenol (DON or vomitoxin). The environmental conditions have been extremely conducive to FHB development this year in areas. Our research sites in both West Lafayette and Vincennes have moderate to high levels of FHB develop in our non-treated susceptible variety checks.
Fusarium head blight management is difficult and requires an integrated approach. This includes selection of varieties with moderate resistance and timely fungicide application at flowering. We are now past implementing either of these management options, but these are important to remember for next year. In addition, it will be important to assess your fields this season to determine if you have FHB. FHB can cause direct yield loss creating seeds that are shriveled and have a rough, sunken appearance to complete head loss. FHB infection can also reduce seed quality and feeding value of the grain due to the risk of mycotoxin (DON/vomitoxin) production in infected seed.
The question now is “I have scab in my field what do I need do?” Here’s a short list.
Document the issues in each field, so you have records for making decisions on future disease management. FHB is easy to see when the head is still green – it will be much more difficult to rate as the heads reach maturity. See images of FHB in the head both at green and more mature stages. You might be able to see the pink salmon sporulation and/or purple-black fruiting bodies on mature heads (Figures 1 and 2). In addition, it is good to note during the season what management tools were attempted – spray date and growth stage of crop, was there variability in the growth stages, weather conditions after fungicide applications. These all can play a role in effective disease management.
Figure 1. Wheat spikes showing bleached florets affected by scab. Salmon to pink sporulation may be visible and can help confirm once the spikes have reached maturity (pink arrows). Dark purplish-black sooty mold can also occur mature wheat heads following infection (black arrows).
Figure 2. Another example of the salmon/pink sporulation on a wheat head.
- It is not recommended to store grain from field with high levels of scab – accumulation of DON and other mycotoxins can continue in stored grain. Suspect grain, if stored, should be dried to less than 15% moisture as soon as possible after harvest, then dry down to less than 13% in storage and kept separate from the good quality grain.
- Planting seed from fields that had moderate to heavy scab is not advisable. The infected seed will have low germination and poor vigor resulting in a thin stand. If going to use this seed, it should be cleaned thoroughly to remove the scabby seeds, and a fungicide seed treatment would be advised to protect germination and reduce seedling blight.
The next question “Why was is it so bad? I followed the guidelines applied my fungicide at flowering but we still have poor control.”
Here’s a few of my observations:
- Moderately to highly favorable environmental conditions for Fusarium head blight (FHB)/scab occurred all spring.
- Many wheat varieties have moderate resistance that help can reduce the risk of sever disease, and fungicides can help suppress the development, but this may only provide about 50% suppression. Therefore, even with the best management programs in place the extremely favorable conditions for FHB have led to high levels of infection this season.
- There was extremely variable growth in individual fields this year – plants ranged from boot to full flower when trying to make a decision on fungicide timing. In addition, fungicides may only provide partial suppression of FHB and timing is a significant issue for obtaining moderate levels of control.
- Frequent rains not only complicated planting, but any and every other trip across the field. Rain events closely following fungicide application may have diluted or washed off applications further reducing expected efficacy.
Additional references:
US Wheat and Barley Scab Initiative https://scabusa.org/
Cowger, C., and Arellano, C. 2013. Fusarium graminearum infection and deoxynivalenol concentrations during development of wheat spikes. Phytopathology 103:460-471. https://apsjournals.apsnet.org/doi/pdf/10.1094/PHYTO-03-12-0054-R
Salgado, J. D., Wallhead, M., Madden, L. V., and Paul, P. A. 2011. Grain harvesting strategies to minimize grain quality losses due to Fusarium head blight in wheat. Plant Dis. 95:1448-1457. https://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-04-11-0309
Fungicide efficacy for control of wheat diseases. CPN-3002. http://doi.org/10.31274/cpn-20190620-031
An Overview of Fusarium Head Blight. CPN-3005. http://doi.org/10.31274/cpn-20211109-0
