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One bad apple…

Rural IndustriesResearch & Development Corporation

16 July 1999

Core rot, the plant disease that turns an apple’s inviting ‘crunch’ into an appetite sapping ‘mush’ has a new enemy.

Research in Tasmania has shown positive results using bees as carriers of biological control agents to combat core rot, reducing disease incidence and also the need by orchadists to do high-volume pesticide spraying during the flowering period for disease control.

Conducted by the Tasmanian Institute of Agricultural Research (TIAR), with support from the Rural Industries Research and Development Corporation (RIRDC), the research could provide significant savings to the industry and enhance Australia’s export image.

Core rot is caused by a fungal infection developed during the flowering stage of apple development, but remains latent until after harvest when the apples are held in controlled atmosphere storage for export or delivery to market.

Because infected apples show no outward signs of having core rot, unsuspecting consumers can be left with the rotten fruit.

Researcher Chris Archer said the inability of producers and wholesalers to identify affected fruit meant a zero tolerance level was being aimed for.

“Apples can be kept in controlled atmosphere storage for up to nine months before export to improve market advantage, so limiting the amount of core rot is obviously important,” he said.
“Because it is impossible to identify apples with core rot, they can inadvertently be sold and affect the quality reputation with customers.”

Mr Archer says bees have long been used in orchards to assist in pollination, and it was only a short step to have them carry a biological control agent during the dangerous blossom period.
Trials conducted last year identified a fungal species which occurs naturally in apples and is a natural antagonism to other funguses which cause core rot. This fungus, when introduced to bee hives is transferred naturally to the blossom.

The system, using a similar control agent has been demonstrated to be effective in overseas trials controlling Botrytis infections of strawberries.

A hopper and swipe trap at the hive entrance, containing the fungus, forces the bees to crawl into and out of the hive depositing ground fungal material onto the bee which is transported to the blossoms.
Trials found the bee transfer was more efficacious in the transfer of material to the flowers than high-volume sprayers to apply potential bio-control agents.

“The use of specific bio-control agents for disease control, combined with the use of honeybees for bio-control agent dispersal offers great promise within other horticultural commodities,” Mr Archer says.

“There is the potential for a win-win situation both for growers and apiarists. Growers benefit with reduced labour and chemical use on farm, while apiarists are able to request a higher fee for placement of hives within production areas during flowering.”

In the next few months, research will concentrate on identifying the fungal isolate (within the identified species), having the greatest ability to control the core rot disease.

“Within any species there is the potential for variation between individuals, each having slightly different characteristics,” Mr Archer said.

“Once the individual isolate has been determined it can then be generated in the laboratory for wider field trials in the coming year.

“The greatest challenge within the project will be integrating the fungal agent within existing fungicide programs that are necessary for the control of other apple disease. This aspect of the research will form an important component of the coming season’s trials.”

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