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NDSU Bee Vector Trials ‘Promising’

Tuesday, October 26, 2021
filed under: Disease

pollinator bags over SF heads
Sprinkler irrigation in the NDSU sunflower head rot study.
Pollinator bags that permit airflow but exclude pollinators
were placed over the sunflower in those treatment plots
where bees need to be excluded.
It seemed too simple. Could it actually work?
        Michael Wunsch was skeptical when a Canadian company approached him about evaluating the use of honeybees to disseminate the biological control agent Clonostachys rosea for management of Sclerotinia head rot in sunflower. 
        “I’ve worked with biologicals before, and I had never seen anything that really worked,” Wunsch says.  “But they were willing to pay for the trial, so I thought, ‘Why not?’ ”
        He wasn’t holding his breath.
        But then he realized that what Bee Vectoring Technology (BVT) was doing actually made sense.  The Canadian company equips beehives with a dispenser that deposits the biological control agent at the exit of the hives, such that bees must walk through the product as they leave the hive.  Bees get it on their bellies and feet and then fly out to pollinate, depositing the biological agent on the sunflower florets.  They repeat this process every day, so as they’re pollinating, they’re dropping that biological agent on each successive ring of florets produced by the sunflower plant.
        “The bees deposit Clonostachys rosea on the sunflower florets as they pollinate, and the biological control agent colonizes the florets without causing any disease,” Wunsch explains.  “Once the biological control agent colonizes the floret, it out-competes Sclerotinia sclerotiorum, causal agent of Sclerotinia head rot.  There’s no room for the pathogen.”
        So far, Wunsch says, it looks promising.
        “What we found is we have gotten very good, consistent control this way,” he notes.  “In field studies conducted in Carrington and Langdon, N.D., we’ve gotten about a 50% reduction in head rot with the biologicals, increased sunflower yield — and reduced contamination of the grain from sclerotia (resting structures of the Sclerotinia fungus).”  In last year’s field studies, the use of bee-vectored biological control reduced the sclerotia contaminants in the grain from 6% by weight to 3%.
        “It’s encouraging for those growing confection sunflower,” Wunsch observes. “The yield bump is big, and the reduction in Sclerotinia looks promising.  The contamination of the grain with sclerotia dropped below 4% by weight, which is crucial if selling for human consumption. Contamination of the grain with sclerotia must be below 4% by weight to sell for human consumption.”

Michael Wunsch
Michael Wunsch

        Wunsch points out these results are using the most suspectible hybrid, so producers who stack this biological agent with a less-suspectible hybrid could be in a good position.
        “This is one of those cases where using a biological makes sense,” the NDSU researcher says.  “Bees deliver the biological daily, right where it’s needed. You can get around problems of how to get fungicide on the sunflower head.  The bees are most active at those times of the day when it’s a little cooler, and that’s the time the biological is most likely to colonize the florets.”
        Wunsch says the dispensers are user friendly and easy to set up.  Beekeepers have been happy to work with the researchers, and they haven’t had any complaints about the product impacting bees.
        Still, Wunsch has more questions.  For example, does activity decrease the farther the plants are from the beehive? Wunsch’s team in Carrington and his collaborator Venkata Chapara, plant pathologist with the NDSU research center in Langdon, set up half-mile strips of sunflower at different distances from the beehives to see if the distance affected the effectiveness.  They’re still compiling data from this year, but the first year of data is encouraging: the biological seems to be effective despite the distance from the hives.  They are also evaluating whether there is a benefit to having bees even if there isn’t disease pressure.
        “Breeders and agronomists have long reported that the use of bees to facilitate outcrossing in sunflower increases yields. As a part of these studies, we are seeking to quantify the impact of bee pollination on sunflower yield.  Sclerotinia head rot is a sporadic disease, and we want to assess whether a grower can expect benefits from bringing beehives to his field even if conditions favorable for head rot do not develop.” 
        BVT’s formulation of Clonostachys rosea is already available commercially for sunflower as well as strawberries, apples, tomatoes, canola and blueberries in Canada. You can learn more at
— Jody Kerzman
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