(Courtesy Peggy Greb/USDA)

(Courtesy Peggy Greb/USDA)

Researchers at the University of Adelaide in Australia are using a bee-delivery system to prevent brown rot in cherry orchards.

The technology has been used in Europe to control strawberry gray mold, but in this application it could lead to effective disease control in grape, apple, pear, stone fruit, and other fruit crops.

Katja Hogendoorn

Katja Hogendoorn

“All commercial cherry growers spray during flowering to control the later development of cherry brown rot,” said Dr. Katja Hogendoorn, a bee researcher in the university’s School of Agriculture, Food, and Wine. She’s leader of the program called Bees as Flying Doctors that developed the non-spray method.

“Instead of spraying fungicide, we’re using bees to deliver a biological control agent right to the flowers where it is needed. This uses an innovative delivery method called entomovectoring,” she said.

The biological control agent contains spores of a parasitic fungus, Trichoderma harzianum, that prevents the fungus that causes brown rot (Monilinia sp.) from colonizing flowers, she said.

“Every morning, the cherry grower sprinkles the spores into a specially designed dispenser fitted in front of the hive. The bees pick up the spores between their body hairs and bring them to the flowers,” she said.

A commercial spray product, called Antagonizer, also uses a Trichoderma line of fungi for cherries. The beneficial fungi were isolated from Australian cherry orchards, and the spray product has been tested extensively, Hogendoorn said. But the use of bees has many environmental and economic benefits compared to spraying fungicide.

“The bees deliver control on target, every day,” she says. “There is no spray drift or runoff into the environment and less use of heavy equipment, water, labor, and fuel.”

This dispenser mounts on the front of a bee hive, where it meters out spores of a parasitic fungus that prevents brown rot. (Courtesy Heikki Hokkanen)

This dispenser mounts on the front of a bee hive, where it meters out spores of a parasitic fungus that prevents brown rot. (Courtesy Heikki Hokkanen)

The spray formulation is not suitable for use with bees, but the manufacturer, Metcalf Biocontrol, is starting to grow a special formulation and will call it Antagonizer for bees, she said. It will also be distributed in Australia by Organic Crop Protectants.

The hive-mounted dispenser Hogendoorn uses is manufactured by a Finnish company, Aasatek.

Hogendoorn says adoption of the technique will create additional demand for bees, building up the honeybee industry and the number of managed hives. “This will help prepare Australia for the expected incursion of the Varroa mites, which is causing great damage and cost to bee and horticultural industries around the world,” she said.

“Brown rot is caused by a fungus that significantly impacts the $150 million Australian cherry industry through costs of applying fungicide, yield loss, and fruit spoilage,” said Hogendoorn, a postdoctoral research associate.

“The flying doctors technology is used successfully in Europe to control strawberry gray mold, but it’s the first time for Australia and the first time in cherry orchards anywhere.”

With increasing availability of suitable biological control agents, the flying doctors technology is expected to become available for disease control on a multitude of crops.

Bees can theoretically be used as flying doctors where the flowering crop is attractive to bees, where distribution of pest control to the flower helps to control the disease, and where a control agent is available that is non-toxic to bees and can be distributed by them (7 to 30 microns in size), she said.

Apple and pear growers spray antibiotics during bloom to control fire blight, and a product called Blossom Protect is thought to use the same principle as Antagonizer. It colonizes sites in flowers with organisms, preventing use of these sites by fire blight bacteria.

“We do not exactly know how it works,” Hogendoorn said. “Trichoderma interacts in many ways with other fungi: There is parasitization, direct competition for space and nutrients, and suppression of growth. Trichoderma can also have beneficial effects on plant health through increasing the systemic resistance of plants. How that works is also unclear.”

The flying doctors project is funded by the Australian government through a Department of Agriculture Innovation Grant. The new method will be available for Australian cherry growers this year. •