Wheat fungicide timing critical

Spraying for fusarium has a short window, so scouting is critical

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Wheat heads are beginning to emerge making growers think about T3 timing to spray to protect against fusarium head blight (FHB).

“Fusarium head blight is still one of the most important diseases in winter wheat,” says OMAFRA cereals specialist Joanna Follings.

Why it matters: For the best protection against FHB, fungicide timing is very important. Optimal spray timing happens in a very short window.

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Meagan Griffiths, precision agronomist with FS Partners in Ayr says she is seeing the flag leaf fully emerged in some areas, while other fields are showing slight emergence of the flag leaf.

“We are probably going to be starting to check for heads in that early wheat, if it’s warm, mid to end of next week and hopefully not be spraying until the week after,” said Griffiths on May 29.

Agronomists and growers refer to a timing guide referencing days “-4 to +4” to the stage of wheat.

Day -3 indicates when the head is in the boot, the tip is still below the top of the stem and has not begun to emerge out. The following three days is when the head will be pushing through and past the flag leaf.

Day zero indicates 75 per cent of the wheat heads within the field are fully emerged and ideally, the optimal spray window is two to four days following this, day +2 to +4 – when the anthers (flowers) of the wheat are beginning to emerge.

It’s important to note temperature plays a large role in determining the time between stages.

“The amount of time to get from day -3 to day +2 could take five days, could take three days, could take over one week. If it’s super hot out, it could go much quicker. If it is very cold, it can be painfully slow. (Growers) need to check back to confirm when anthers are poking out like you want,” says Griffiths.

Griffith says one of the biggest mistakes she sees is producers spraying the crop too early. It’s best to spray when anthers are visible.

“You want at least 50 per cent of those (75 per cent emerged) heads starting to poke out those anthers – the little yellow anthers in the middle of the head. You probably then have a four or five-day window depending on who you talk to.”

For growers using precision agriculture platforms, such as Climate FieldView, it’s ideal to use the system’s NDVI (normalized difference vegetation index) map to correlate when 50 per cent of their field is at the proper stage for spraying.

If the field is showing high variability, Griffiths says it’s best farmers focus on the staging of their high yielding areas and stage the whole field based on that.

“We want to be managing for what the majority is, but also what the highest yield potential is for that field. If you have 50 per cent (showing anthers) on the nice dark green areas of your NDVI, I would stage the field based on those areas knowing they’re going to have the highest yield potential.”

Following the timing of T3 application, coverage is also very important. Low winds are ideal, but also use of the proper nozzles.

“Some sort of nozzle that has a forward and a backward pointing nozzles. You are wanting to hit that head horizontally because it’s a vertical target.”

The risk for FHB is greatest during wet, humid weather around the flowering period.

“Fields where cereals have been seeded following corn or other cereal crops are most at risk,” says Follings.

Farmers can check out the DONcast model for the potential risk of FHB infection found at www.weathercentral.ca and pay close attention to the weather forecast.

Growers can use Publication 812, Field Crop Protection Guide 2020-2021 to find the best fungicide to use on their operation.

About the author

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Jennifer Glenney

Jennifer is a farm reporter who lives in Cayuga, Ontario.

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