Is Our Strategy For FHB Management Good Enough?
Fusarium head blight is a well-known disease for wheat producers and is always a hot topic mid-season. Mostly, we evaluate weather patterns leading up to or during heading to determine if its wet/humid enough to require fungicide application and the conversation doesn’t go any deeper than that.
However, a few questions have come up for myself and from customers over the years that I wanted to investigate:
1. What happens if the disease infects before or after ideal fungicide timing?
2. Is the risk of FHB reduced if we have experienced repeated years of dry conditions?
3. Are current fungicide timing recommendations the most optimal to prevent the disease?
First, a quick review:
Fusarium graminearum is not soil borne. It survives on all types of plant residues including roots, crown tissues, stems, leaves, seed. Vomitoxin or DON is the toxin that is produced by Fusarium graminearum as it infects the seed - This factor is important for producers of feed wheat.
The primary infection for FHB starts when wind spreads spores from infected residue onto head tissues when the head emerges. 10-14 days later (with proper conditions) we start to see symptoms on the head. If wet conditions persist, the fungus will spread by rain splash throughout the head and onto neighboring heads. This secondary infection may not show up as Fusarium Damaged Kernels (FDKs) but it will contribute to DON accumulation.
Now to answer the list of questions:
1. Effect of Infection Date
Fusarium can infect the head at any point after the head emerges, even in the absence of flowers. Early infections (anytime from flowering to mid-milk stages) will lead to higher levels of “tombstone” kernels/Fusarium damaged kernels – these may or may not end up in your sample. Many of these kernels are so small and shrivelled that they will blow out the back of your combine. With late infections (during milk stages), you may not see many FDK but it can contribute to high DON accumulation and will still allow for the disease to carry over on residue.
2. Will the risk of FHB infection be reduced if we experience repeated years of dry conditions?
Yes, dry conditions during heading will result in few FDK symptoms – and therefore less risk of downgrading at the elevator. HOWEVER, if the season had moisture in May/early growing season, the fungus can still infect plant tissues and dry conditions slow down the rate of residue decomposition which will also extend the lifetime of the disease presence in a field.
3. Are current fungicide timing recommendations accurate?
The Manitoba Guide to Field Crop Protection states “apply at 75% of heads are fully emerged until 50% of heads are flowering”. If you spray on the early side there are likely 25% of heads or later tillers that aren’t being covered by that application and are left unprotected. Success of fungicides is dependent of head coverage – otherwise, we have a higher risk of seeing that secondary infection of spread within the head and between neighboring plants.
Dr. Kelly Turkington (Agriculture and Agri-Food Canada) suggests that with current recommendations and products we will get suppression at best. The level of control by fungicides is approximately 50% for FHB and even less for control of DON. This is different that the control we get of leaf diseases with fungicides – which is very high level of control. In the link below – Dr. Turkington dives deeper into an integrated approach that helps overcome this limitation to fungicide control.
Since early infection is typically what leads to the most Fusarium Damaged Kernels and therefore the most downgrading at the elevator, this is the stage that we choose to protect most. However, it is not offering us complete protection from carryover on residues.
In summary, I think it’s easy to just keep doing what we’ve been doing when it comes to management of Fusarium Head Blight but looking deeper and paying closer attention to detail will be the difference maker when it comes to yield AND quality of our wheat.
~Katie Meggison
Relevant links:
YouTube: Wheat School – The Difference Between Vomitoxin and Fusarium
YouTube: MAC 2024 – Fine Tuning Your Fusarium Head Blight Management Toolbox