Pupae from the Queensland Fruit Fly have been found in a sample of peaches from a Harcourt tree.
The town was previously thought to be free from fruit fly, which has infested Bendigo in recent years.
Harcourt Valley Fruit Fly Action Group member Terry Willis said an interim report showed the fruit fly in eight peaches from a backyard tree.
The fruit fly attacks fruit and vegetables, making their produce inedible.
Mr Willis said the next step for Harcourt was to initiate an Emergency Action Plan.
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