Features Desiccants Seed & Chemical
Some points to remember about sunflower desiccation

For farmers with sunflowers in their 2011 cropping plan, it is recommended they take a bit of time this winter to work through the options for drydown next fall. Natural drydown is ideal; however, the sunflower fields of southern Manitoba and Saskatchewan are likely to have less than ideal conditions, and desiccation may be needed.

The key management stage for desiccation is when the sunflower is mature and ready to seriously dry down. The seeds stop filling and begin separating from the head (also known as the “receptacle”).

According to growers and extension workers, the fat head holding all the seeds would make a reasonably good sponge. It holds moisture long after the seed is dry, and will soak up new moisture with any passing shower. If the head cells are ruptured by a desiccant, the fat head may hold more water. Unfortunately, as seen in 2009, head rot will develop if the head dries too slowly. If harvesting starts too soon, of course, it can lead to grief as the heads holding too much moisture turn to mush inside the combine. “Typically, frost is your best desiccant for sunflowers,” says Anastasia Kubinec, Manitoba oilseed specialist from Carman, Manitoba. “If it’s minus six for four hours, your plants are already desiccated. However, for the past three years we’ve had wet weather in September along with later frosts. After the issues we had with head rot in 2009, more guys have been looking at desiccating.”

Reglone, produced by Syngenta Crop Protection, is the only product in Canada registered as a sunflower desiccant. If conditions are suitable, Reglone will shave a week or two off the drydown process, potentially reducing vulnerability to birds, seed loss and quality loss.

Protecting the value in a quarter-section of sunflowers, a $5000 Reglone application has the potential to be a really good investment. “If it’s the difference between 1800 pounds or only 800 pounds per acre of sellable product, it’s definitely worth it,” says Kubinec.

Staging that $30-per-acre aerial application is not easy. A few days of dry weather following the application is optimum. The crop already should be down to 35 percent moisture, or less. Watching forecasts for five-day dry weather outlooks and hoping for dry weather with killing frost are as much as growers can do about keeping conditions dry. “You really have to keep an eye on what the weather conditions are going to do,” says Kubinec. “These past couple of years have been very touchy. Your crop may be at the right stage, then you hear it’s going to rain. The choice then has to be made: do you wait until the rainy period is done and then desiccate, or can you get it on before the rain and have enough time for the crop to start to dry down?”

Desiccating at the wrong time has led to horror stories. “If it rains right after desiccation and stays wet for two weeks, your head rot level can actually increase,” she says. “Or, if you desiccate a little too early, there can be less than the optimum yield.”

Line on the bract
Specialists advise, therefore, that growers take time to evaluate the maturing sunflowers even as other harvest programs are in full stream. That sweet spot, at 35 percent moisture, is likely to drive by in September while growers are focused on canola or small grains.

According to Kirk Howatt, weed scientist with North Dakota State University in Fargo, this is one case where monitoring the field is the most effective way to determine when it is ready to desiccate. He advises growers to look at the sunflower heads; ignore the leaf tissue and even the seeds as a measure of readiness for a desiccant. Due to a strong stay-green trait in newer sunflower varieties, the time to apply the desiccant may appear to be while leaves are still quite green and healthy. Instead, Howatt advises growers to examine the back of the head and the bracts that surround the edge. Bracts are outer scale-like leaves (see illustration).

Look first for a colour change, from green to yellow, on the back of the sunflower heads. It probably will occur in late August. Next, look at the bract layer. As drydown begins, a brown edge appears first at the tapered top of the bract. Gradually, a brown edge line develops down along the bract sides.

When that brown edge reaches the shoulder of the bract, it is close to 35 percent moisture. At the ideal point, the lower half of the bract changes colour. The lower half becomes solid brown and meets the remaining yellow portion above as a clear brown-yellow line in the bract. “Once it’s there, it’s pretty consistently at 30 to 35 percent moisture, depending on the hybrid,” Howatt says. “Once they get that brown discoloration of tissue down to the shoulder region of the bract, we’re around 35 percent moisture or below.”

Several years of drydown research in North Dakota, using glyphosate, Paraquat and Sharpen (BASF Kixor herbicide with the active ingredient, saflufenacil), at various maturity stages convinced researchers that bract colour change was the most reliable indicator of moisture. “No moisture tester is accurate in the 30 to 35 percent range,” Howatt says. “We did moisture tests a number of ways, including oven drydown. When we put all the information together, that brown line across the bract was the most reliable and, it was easy to see.”

Seeds do dry faster than receptacles (heads). Seed is ready for desiccating weeks before the tissue in the head is ready for harvest. “In our studies, our seed moisture often is down well below 15 percent when the head moisture and all that spongy material is still up above 60 percent. That spongy tissue needs to get down to about 40 percent before it combines easily.”

Growers also need to remember that ripening occurs unevenly in individual sunflower heads and in whole fields. “Get up on something and look to see how even it is across the field,” Howatt says. “If you see definite islands of green out in the middle, pay attention to how much is still green versus the stuff that’s turning brown. To evaluate it, you may need to walk out into some of those greener areas before you desiccate.”

Kubinec and Howatt agree that during crop planning is a good time to put a desiccant application in the budget and to arrange for an aerial applicator to be on standby for the following September.

If it is in the plan to do a chemical drydown, and the ideal brown line on the bract stage goes past, it may not be too late. Still, they say, at 30 percent moisture a desiccant application can reduce the drydown period and save yield.