North Dakota State University Research Uses Bees to Prevent Disease in Sunflowers

In partnership with: North Dakota Department of Agriculture

Bees are the unsung heroes of the agriculture industry – without them, we wouldn’t have many crops for food and feed. Besides their already important job of pollinating, what if bees could be put to work to prevent disease in certain crops?

“North Dakota is one of the top producing states for confectioner type sunflowers,” says Deanna Gierszewski, North Dakota Department of Agriculture Specialty Crop Block Grant program administrator. “We’re also No. 1 for honey, so we have a lot of bees in the state.”

These two stats came together for a creative solution to a devastating disease.

The Budding Problem

Sclerotinia head rot develops on sunflowers when cool, wet weather occurs during bloom in North Dakota, Minnesota and Manitoba. South Dakota has fewer issues with Sclerotinia head rot because it’s a bit warmer. The disease causes sunflower kernels to fail to develop or become bitter, developing hard, black structures called sclerotia that mix with sunflower seeds at harvest.

This disease makes it more difficult to ensure a quality final product because “the sclerotia are similar in size and weight to sunflower kernels and can’t be separated by processors,” says Michael Wunsch, researcher at the North Dakota State University Agricultural Experiment Station in Carrington. “In addition, the Sclerotinia pathogen produces toxins that cause sunflower kernels adjacent to diseased tissues to become bitter.”

Sunflower processors have a 4% threshold of sclerotia by weight in loads of confection sunflowers. If a sunflower grower is unable to sell a load for human consumption, he might be able to find a birdseed market but will still take a financial hit.

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Existing efforts to prevent this disease have their own shortcomings. Applications of biological control or synthetic fungicides via traditional application methods are less effective due to the difficulty of achieving deposition of foliar sprays to the sunflower heads.

“It is very difficult to achieve satisfactory deposition of foliar sprays to the front of sunflower heads due to the position of the heads,” Wunsch explains. “Even with the best application methods, foliar sprays are deposited to only a small proportion of floret buds on sunflower heads. Modern fungicides move upward with water in plant tissues, but that doesn’t work for Sclerotinia head rot because the fungicide doesn’t move laterally between buds.”

A Buzzing Solution

Making the most of the daily habits of our fuzzy friends, Wunsch is studying how bees can transport spores of Clonostachys rosea, a fungal biological control agent that prevents sunflowers from developing Sclerotinia head rot.

“The spores of Clonostachys rosea colonize the sunflower petals, making the tissue inhospitable for the pathogen,” Wunsch says. “We’re taking advantage of bees naturally collecting nectar just as sunflower florets enter bloom, shortly before the florets become susceptible to Sclerotinia.”

Bees are well-suited for delivering the biological agent to sunflowers. Bee boxes are outfitted with a dispenser that deposits a powder of the biological control agent as bees exit the hive. The bees crawl through the powder, getting spores on their feet, legs and stomach.

“Sunflower heads have lots of flower buds, and each day, the outermost buds bloom,” Wunsch says. “The bees deliver the biological control agent to sunflowers daily, protecting each ring as it opens.”

Bloom duration depends on temperatures, lasting from seven days to up to two weeks, progressing faster if it’s hotter. Daily delivery of the biological control agent gives the agent time to establish itself, leaving no room for the pathogen to infect.

“This is one of the most promising strategies for managing Sclerotinia head rot in sunflowers,” Wunsch says. “Crop rotation is of limited effectiveness for this disease due to the broad host range of the causal pathogen and persistence of the pathogen in the soil. Resistant hybrids are unavailable. Oilseed sunflowers differ in their susceptibility to this disease, but in a bad year, even the best oilseed hybrids will develop head rot in 20 to 25% of plants. Almost all confection sunflowers are highly susceptible to head rot.”

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Sclerotinia head rot causes significant quality problems, but thanks to the bee method, there are promising results for prevention.

Wunsch has been researching bees since 2016, conducting 10 trials at three different locations, averaging 50% control of head rot. Bee vectoring has kept saleable loads under the 4% threshold 90% of the time – ensuring that sunflower producers are paid for the crop.

Plus, vectoring has no impact on the bees or honey production – a win-win for sunflower growers and beekeepers.