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Lots of advantages to desiccating sunflowers

The key is timing and determining if the crop is good enough to justify the additional cost

Desiccating sunflowers too early can cut yield and test weight. Ideally seed moisture at the time of desiccation will be 14 to 16 per cent, or at least under 20. The back of the sunflower head can be a guide. The bracts in the photo on the left are not fully brown to the bottom. Seeds in this head will be about 30 per cent moisture. The bracts on the right are brown to the bottom and the back of the head is tan coloured. The seeds will be 15 to 20 per cent moisture.

Desiccating confection or oilseed sunflowers to speed up harvest can deliver profits and peace of mind, but timing is everything, says Anastasia Kubinec, Manitoba Agriculture’s manager of crop industry development.

“There has been a move to more producers going to desiccating sunflowers because they do see the economic benefit to it,” Kubinec said during the CropTalk Westman webinar Sept. 13.

“If your yields are going to be down because of weeds or disease maybe it’s not going to be the thing for you to do.”

Manitoba sunflowers are two weeks earlier than last year, she said.

Desiccation will cost $16 to $25 an acre depending on the desiccant, rate and cost of aerial application, she added.

Weather is another factor to consider. If a killing frost (-4 C for four to six hours) is in the forecast farmers can save money letting Mother Nature do the desiccating.

“Sunflowers are extremely hardy and with that fleshy head on the back of the sunflowers it needs to be cold for an extended period of time to really break those cells for the water to drain out and that desiccation to occur,” Kubinec said.

Farmers shouldn’t desiccate ahead of heavy rains, especially if the sunflowers are infected with head rot (sclerotinia). The combination speeds up the breakdown of infected sunflower heads making a bad situation worse, Kubinec said.

However, since desiccants kill by contact not systemically, a little bit of moisture, such as dew, can spread the chemical across the head providing better results, she added. That’s why it’s best to apply a desiccant in the morning or evening, Kubinec said.

Desiccation can get a good sunflower crop in the bin earlier. The longer it stands in the fields the more vulnerable it is to breakdown if it’s diseased or blackbird predation. There is no control or deterrent for blackbird feeding, Kubinec said.

“We probably lost 40 per cent to blackbirds (in one field that couldn’t be desiccated),” said Kubinec, who also farms with her family. “Fields right across the highway from each other — one desiccated and one not — that is some of the difference if you are not desiccating. There is real potential that you could lose crop yields because of the blackbirds.”

And then there is just the “sanity” factor.

“I never want to combine sunflowers in the snow,” Kubinec said. “My father and grandfather quit harvesting sunflowers because they were always harvesting them in the snow. With a desiccant product we have been growing sunflowers for about eight years. We always seem to be able to get them off in September or October, which is great for everybody.”

Earlier harvest generally also means improved crop quality. The trick is determining when to apply a desiccant. Applying too soon will reduce yield and test weight. Some confection sunflower buyers require a minimum test weight and pay less if it isn’t achieved, she said.

Determining when to apply a desiccant is a matter of watching and waiting, watching and then acting.

It’s best to apply a desiccant between the R8 and R9 stage.

“It’s not a true R9 where the back of the (sunflower) head is that tan colour,” Kubinec said. “It’s really before that stage when the back of the head is really yellow and it’s started to turn brown with that tan colour and the bracts are brown and brown all the way down… then your seeds are 14 to 16 per cent moisture, or maybe up towards 20 per cent, but that’s the stage we want to be desiccating. You want to make sure that most of the field is 20 per cent (moisture) or less.”

The back of the sunflower head and bracts are guides, but before desiccating farmers should shell out seeds from five or so heads and test the moisture level, Kubinec said.

If a moisture tester isn’t available, or not calibrated for sunflowers, Kubinec recommends the microwave test:

1) Weigh, in grams, some seeds, then place the seeds in a safe container and microwave on high for two minutes.
2) Repeat at least twice, and until there is very little difference between the pre- and post-microwave weights.
3) Calculate the moisture level by subtracting the dry weight from initial weight, then divide by the initial weight and multiply by 100.

Here are some field aids for assessing moisture levels:

  • If the seed coat can be scuffed or peeling it’s more than 18 per cent.
  • If it’s soft and hard to crack it’s around 18 per cent.
  • If it’s firm, but not always cracking it’s 14 to 15 per cent.
  • If it cracks easily it’s under 13 per cent.

There are only two desiccants registered for use on sunflowers in Canada — diquat (Reglone) and Heat (saflufenacil).

Both work best when applied with lots of water and when temperatures are above 20 C. They take longer to dry down sunflowers when temperatures are cooler.

Diquat works in seven to 10 days, depending on the weather. The pre-harvest interval is 15 to 20 days. It’s more expensive than Heat and may not always be available at local retailers, Kubinec said.

“The benefit is it’s always consistent,” she added. “It really does a good job.”

Heat takes 10 to 16 days to desiccate sunflowers, but has a shorter pre-harvest interval of seven days.

Heat hasn’t been used that long on sunflowers so more information is needed on how well it works, Kubinec said.

Glyphosate is not registered for pre-harvest use on sunflowers in Canada, she added.

About the author


Allan Dawson

Allan Dawson is a reporter with the Manitoba Co-operator based near Miami, Man. Covering agriculture since 1980, Dawson has spent most of his career with the Co-operator except for several years with Farmers’ Independent Weekly and before that a Morden-Winkler area radio station.



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