Time the FHB fungicide right this year

Fusarium head blight (FHB) is one of the major fungal diseases that impact grain yield, grain quality and mycotoxin contamination in cereal crops. FHB requires an integrated management approach; however, fungicide is the most important in-season tool to manage FHB.

Fungicide timing is crucial for an effective application. The current recommended timing on the Alberta Bluebook is:  

It might be the application window you are most familiar with. However, it might seem narrow. With less than a week of application window, unfavourable weather like wind or rain may delay the application.

This brings further questions: 

  • Are later fungicide applications still effective in managing FHB?
  • If I want to apply early, how early is too early?

Are later fungicide applications still effective in managing FHB? 

The short answer is: yes, fungicide is still effective in FHB suppression when applied up to 10 days after early flowering, when the crop reaches the end of flowering and early grain filling. 

This conclusion is drawn from multiple studies, done on multiple crops, with different fungicide products and in different growing regions. A few examples:

Example No. 1:  

  • Locations: Saskatoon, Outlook, Melfort, SK
  • Crop: Durum
  • Fungicide: Caramba

This study found that, when FHB disease pressure is high, a later fungicide application at the end of flowering (BBCH 69) to early milk (BBCH 73) produced equivalent FDK, DON and test weight compared to applications at early to mid-flowering.  

Figure 1. Fungicide timing effect on DON of susceptible durum variety, CDC Desire. Note: numbers sharing the same letter code are considered statistically the same. Photo credit: G. Singh and Spayers 101.

Example No. 2

  • Locations: Melfort, SK; Scott, MB; Brandon, MB
  • Crop: CWRS wheat
  • Fungicide: Prosaro XTR

Another study done on CWRS wheat in SK and MB also showed the late fungicide timing, 7-10 days after early flowering or 10-14 days after full head emergence, produced similar FDK% compared to the ideal application timing of early flowering. 

Figure 2. FDK% as impacted by fungicide timing treatments. Credit: Kelly Turkington.

Example No. 3 

  • Location: North Dakota
  • Crop: winter barley
  • Fungicides: Prosaro, Miravis Ace, Caramba

Trends similar to the previous 2 examples are found on winter barley, based on study done by North Dakota State University. Across three fungicides, a later application at 6 days after head emergence is equally or more effective compared to application at BBCH 59 (head fully emerged).

Figure 3. optimal timing to apply fungicide to winter barley for FHB suppression. Figure courtesy: Christina Cowger, USDA-ARS Small Grains Pathology, NCSU.

The three examples above span across different regions, crops and fungicide products. They all come to a similar conclusion: fungicide applied at late flowering to early milk stage is as effective at FHB suppression as application at early flowering stage.

Practical recommendation: applying the fungicide at late flowering to early milk stage is still effective. If fungicide application is not possible at the ideal stage of early flowering, consider still putting the fungicide on if FHB risks are present. 

If I want to apply early, how early is too early? 

The short answer: applying fungicide before the head has fully emerged may reduce the efficacy of the fungicide.

The reason is that the FHB fungicides are locally systemic. In other words, they do not redistribute up or down the heads. To be effective, the droplets need to land on the spikelets to protect the developing kernel from the disease. This requires good coverage.  

When the heads are partially emerged, the fungicide can only protect the part of the heads that have emerged. The part of the head that had not emerged will be unprotected and more prone to FHB. Such impact can be found in Example No. 3 above, where grain DON contamination is the highest when the fungicides are applied at 50% head emergence. 

Takeaways 

  • Application timing is important in effective FHB suppression.
  • Fungicides applied 7-10 days later than the “ideal stage” on the label is still effective in reducing FDK and DON. So if application at the ideal stage of early flowering is not practical, it is still worth putting on the fungicide at late flowering-early milk stage, if the disease pressure is high (refer to prairiefhb.ca for FHB risk maps) .
  • Avoid applying the FHB fungicide too early. If possible, wait till the heads have fully emerged to achieve a good coverage and most effective protection.

Additional resources: 

Fusarium head blight control in durum wheat – Canadian Agronomist   

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