If a hard frost isn’t in the forecast, sunflower farmers might want to consider applying liquid frost — a.k.a., a desiccant.
That’s the advice Manitoba Agriculture oilseed specialist Anastasia Kubinec gave during the Crop Talk Westman webinar Sept. 28.
Kubinec, who also farms with her husband and father, knows of what she speaks. Their sunflowers were harvested in September and are in the bin.
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“Getting those sunflowers off your field early can mean a lot of great things,” Kubinec said. “You will have better quality, less head rot and you are probably going to have some better yields. You’re not losing those seeds to birds or losing them potentially to disease.”
But there’s lots to consider first. One is the weather forecast. If a hard frost is looming, nature will dry down the crop for no cost. By “hard” Kubinec means -4 C for four to six hours.
“You need it to be really cold for four to six hours to freeze and explode those cells to cause it to rapidly desiccate,” she said.
Economics is the other consideration. Diquat is an effective desiccant, but it’s expensive and there’s the aerial application cost on top.
Heat is less expensive but slower.
If the sunflower crop isn’t expected to yield well, adding more production cost doesn’t make sense.
“My top reason for desiccating is basically to speed up harvest,” Kubinec said.
The longer sunflowers are in the field, the more susceptible they are to losses from head and stalk rot, lodging and bird predation, she said.
Sunflower heads infected with head rot explode when the combine header hits them and the seeds hit the ground. If infected with stalk rot, winds can knock the plants over making them difficult to harvest. And if blackbirds are near they’ll turn the crop into a buffet.
Kubinec said her father and grandfather dropped sunflowers years ago, when desiccants weren’t used, “… because, as my dad said, he does not like combining in December and he hates combining in the snow.”
Better management tools have prompted a reconsideration of the crop, Kubinec said.
“With some of these desiccation products, we have moved back into sunflowers. It is working well for us. We are combining in late September or October, which works great. You can get into the field faster. You still need to watch seed moisture and that head tissue still threshes out in the combine.”
Timing is important when desiccating sunflowers. Apply too early and the crop will lose yield and quality, Kubinec said.
A desiccant should be applied at the R9 stage. That’s when the back of the sunflower head is yellow and the bracts are brown.
The colour of the bracts can help growers determine the crop’s stage.
As dry-down begins, a brown edge appears first at the tapered top of the bract, a National Sunflower Association of Canada brochure says (http://tinyurl.com/zghptvj). The bract tip turns brown at 40 to 50 per cent moisture. At this stage seed moisture is too high and the plant has not reached physiological maturity. Gradually a brown edge line develops down along the bract sides. When the bracts are brown seed moisture is between 30 to 35 per cent. The broadest part of the bract should be turning brown. At this stage seeds are between 30 to 35 per cent moisture and a desiccant can be applied.
“I am very careful about staging,” Kubinec said.
“I try to go when 80 per cent of the field is at this stage when the bracts are brown and then wait a couple of days just to be on the safe side. And for the past couple of years that seems to have worked pretty good. The test weight has been fine and we have still got it off earlier than waiting for a fall frost and we were pretty happy with results using a desiccant.”
North Dakota State University has an app to help farmers determine sunflower stage. Since it’s based on growing conditions in different North Dakota fields, it won’t be exactly right for Manitoba fields, but the app is a good indicator of when to be checking maturity, Kubinec said.
The weather before and after desiccating is also important. Delay spraying if rain is in the immediate forecast, Kubinec said.
“A desiccant causes the plant to dry down quickly and if there is head rot there it could potentially advance it if we get wet weather,” she said.
“We spray our own fields when I know there is a three-day window of no rain and it looks like it’s going to be really, really, sunny and hopefully temperatures are getting up to that 20 C.”
Desiccants also work faster with warmer temperatures. Normally this late in the season 20 C days are rare so dry-down will take longer — probably 16 to 20 days (in the absence of a heat wave), Kubinec said.
“But it is definitely faster than nature — unless there’s a hard frost in the forecast.”