LANGDON, North Dakota — Honey bees appear to be an effective way to deliver head rot control to sunflowers, North Dakota State University Research studies show.

Venkat Chapara, an NDSU plant pathologist at the Langdon Research Extension Center, for the past two years has been working with Bee Vectoring Technologies International, based in Ontario, Canada, on the field research project using honey bees.

Venkat Chapara, a North Dakota State University Extension plant pathologist, carries a bag of sunflower heads to a collection site during the hand-harvest of the NDSU Langdon Research Extension Center crop plot on Nov. 1, 2021.
Ann Bailey / Agweek
Venkat Chapara, a North Dakota State University Extension plant pathologist, carries a bag of sunflower heads to a collection site during the hand-harvest of the NDSU Langdon Research Extension Center crop plot on Nov. 1, 2021. Ann Bailey / Agweek
Field research conducted in 2020 and 2021 at LREC using honey bees to distribute CR-7 to sunflowers, and two years of previous research in a controlled setting at the NDSU Carrington Research Extension Center using bumble bees shows that the insects are an effective control distribution method, Chapara said. The bees delivered CR-7, a naturally occurring fungal organism, known as clonostachys rosea, to the plants.

Finding an effective way to control sunflower head rot is important to farmers because the disease causes significant yield loss. However, control of Sclerotinia, commonly called white mold, is difficult to control by foliar spraying because it occurs deep in the sunflower heads.

“Fungicides are a good tool for farmers, but, somehow, with head rot, it wasn’t effective, so we’re trying a new method,” said Randy Mehlhoff, LREC director.

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Randy Mehlhoff, North Dakota State University Langdon Research Extension Center director, clips the head off of a confectionary sunflower head that is in a six-acre research plot during the hand-harvest of the field on Nov. 1, 2021.
Ann Bailey / Agweek
Randy Mehlhoff, North Dakota State University Langdon Research Extension Center director, clips the head off of a confectionary sunflower head that is in a six-acre research plot during the hand-harvest of the field on Nov. 1, 2021. Ann Bailey / Agweek

Although total control of head rot in sunflowers isn’t feasible, the LREC and Carrington Research Extension Center research shows that using bees will reduce the amount of damage to the heads, Mehlhoff said.

“The best case scenario is that we would have something for producers to use that would reduce the effect of head rot in sunflowers. That's our real goal, to see if the benefits outweigh the costs,” he said.

North Dakota leads the United States in honey production, and many of the hives are in northeast North Dakota, so it seemed logical to use honey bees to conduct the LREC project, Mehlhoff said.

During the 2021 flowering season, an Aneta, North Dakota, beekeeper placed six hives of honey bees adjacent to a six-acre confectionary sunflower field about 10 miles northwest of Langdon for about 50 days.

The honey bees distributed CR-7, which blocks fungi from causing disease, by walking through a tray dispenser of inoculating powder before they exited their hives. As the bees foraged the sunflowers, the powder clinging to their fur dropped spores of the biological agent onto the flowers, Chapara said

After the sunflower absorbs clonostachys rosea and germinates, it then waits for the pathogen to infect the plants. Once that occurs, the waiting agent, in turn, infects the pathogen, which blocks the disease, Chapara said.

During the LERC sturdy, Chapara also covered some of the sunflower heads with plastic bags so the honey bees were unable to forage in them.

Sunflowers that were covered by plastic bags so honeybees couldn't deliver CR-7, a biological control agent, to them showed greater damage from head rot. The infected sunflowers heads, which are the light-colored ones in the photo, and the healthy heads were hand-harvested on Nov. 1, 2021. 
Ann Bailey / Agweek
Sunflowers that were covered by plastic bags so honeybees couldn't deliver CR-7, a biological control agent, to them showed greater damage from head rot. The infected sunflowers heads, which are the light-colored ones in the photo, and the healthy heads were hand-harvested on Nov. 1, 2021. Ann Bailey / Agweek

In early November, Chapara and about a dozen other Langdon Research Extension Center employees spent a few days hand-harvesting 6,000 covered and uncovered sunflower heads. The harvest involved clipping the heads and carrying them in large, burlap bags to a research center combine that extracted the seeds and dropped them from a hopper into a small bag.

The collected seeds will be cleaned, and then weighed to determine yields. The yields of the uncovered heads and covered heads then will be compared.

Mehlhoff’s visual observations while he was clipping the heads off during the hand-harvest lead him to believe that the second year of the LREC research project, like the first year, will show that the bees are an effective control method, he said.

“It looks like we have a big benefit here. We have a benefit for the beekeepers, a benefit for the sunflower growers and a benefit for those who like to eat sunflower seeds,” he said.