Study looks at link between pollinators, sunflower yields
March 6, 2018
One-quarter to one-third of confection sunflower yields are due to pollination from bees, and sometimes the benefit might be greater.
This is one of the conclusions of a just-concluded two-year research project involving Nebraska, South Dakota and North Dakota.
The study also concluded that there are two ways to ensure or improve bee pollination of sunflowers. One is selecting plant traits that will bring more bees to visit, such as the physical characteristics of florets (floret depth, for example). "This is an area we are currently pursuing," the authors wrote. "We hope to provide genetic markers for bee-related plant traits and information on potential trade-offs."
The other way is to change the pollinators – which could include creating nesting habitat, rearing pollinators or breeding domesticated bees to prefer sunflowers. Some of the pollinator changes could be costly and complex, the paper acknowledged.
"This type of research could be pursued in the future, but would likely depend on finding a person with very specific experience and expertise, as the time and effort required would be substantial," according to the authors.
Jeff Bradshaw, Extension entomologist at the University of Nebraska-Lincoln Panhandle Research and Extension Center, was one of the article authors and co-principal investigators in the study. The other authors are Jarrad Prasifka of U.S. Department of Agriculture Agricultural Research Service, Fargo, N.D.; Rachel Mallinger of the University of Florida; and Adam Varenhorst of South Dakota State University.
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Bradshaw said new data from the study shows hope that sunflower breeders can breed new lines with improved seed set due to pollinator action. This is because traits such as floret depth, which affects desirability to pollinators, is probably inheritable – it can be controlled by genetics.
The knowledge that pollinators can improve sunflower yields also adds a management consideration for sunflower growers, he pointed out. For example, what are the trade-offs between using certain pesticides to control pests such as seed weevils or sunflower head moths, and losing seed set attributable to bees that would be affected by the pesticide?
He noted that more research is needed to answer many of the new questions such as this that have been raised, including pollinator-safe pest management.
Nebraska typically ranks fifth or sixth among sunflower-producing states in acres planted. North Dakota and South Dakota have the most acres by far, followed by Nebraska, Colorado, Kansas, Minnesota and Texas.
Sunflower acreage and state ranking can vary widely from one year to the next, according to the USDA National Agricultural Statistics Service. For example, in 2016, Nebraska had 41,500 acres of sunflowers planted, including both confection and oil classes. In 2017, the total planted acreage was 61,000.
The study was funded by National Sunflower Assocation and State Board of Agricultural Research of North Dakota (SBARE) and results were presented at the 2018 NSA Research Forum.
Scottsbluff, Neb., was among the sites of the sunflower test plots. In 2016 and 2017, test plots were set up in each of the three states with 10 confection sunflower hybrids, five identified as pollinator-dependent and five as not pollinator-dependent. In each plot, sunflower heads were randomly picked for two treatments: open to insect pollinators or bagged with mesh to exclude insects during bloom.
The study had three objectives:
First, to evaluate the benefit of insect pollination for yields, and determine whether yield increases due to pollination vary from one region to another and one year to another.
Second, to determine whether insect pollination has a relatively greater effect on seed set in the center of the head compared to the periphery (in North Dakota only).
Third, to measure the efficacy of different types of insect pollinators, including honey bees, wild bees and syrphid flies, in order to develop alternative managed pollinators.
In analyzing yield data, researchers found that 2016 results differed from 2017. In 2016, the relative benefit from open pollination differed greatly, as did the number and identity of hybrids that were pollinator-dependent. In Scottsbluff especially, yield increases of 120 percent were seen from pollinator visits. It's possible that the big disparity in Scottsbluff is due to temperatures and UV exposure conditions at Scottsbluff, the authors speculated.
In 2017, yield still increased significantly under open pollination, but the increase ranged from 31 percent to 35 percent.
Pollinators have more effect when they visit a plant more frequently and pollinate more florets per visit. The study tracked the types of bees that visited the sunflowers and the frequency of their visits, by group: bumble bee, honey bee, large-bodied solitary bee, small-bodied sweat bee and green sweat bee. The most common by a large margin were the large-bodied solitary bees, followed by bumble bees, small sweat bees and honey bees.
Per-visit observations showed that female large solitary bees pollinated the most florets, followed by small-bodied bees and male solitary bees.
Because most of the solitary bees are ground-nesting, the researchers said opportunities might be limited to develop these species as pollinators. However, certain soil or habitat conservation practices could potentially play a role in improving nesting habitat for such species.