DPI state operations manager of fruit fly Bill Ashcroft said the pest had been detected in Swan Hill and surrounding areas last week.

"We need to make it clear that we don't have an outbreak in Swan Hill, but we are doing exploratory work," Mr Ashcroft said.

"We're trying to identify a source and we are trying to clean it up.

"In Swan Hill itself we have a regular monitoring program for fruit fly...our officers go from door to door and check through trees to see if fruit is neglected and if there's larvae on those trees."

Mr Ashcroft said stone fruit was most susceptible to fruit fly, and the recent humid spell in Swan Hill was likely to make the situation worse.

"We're coming off the back of the worst year we've ever had and this season shapes as being a challenging one because we're getting that wet, humid weather," he said.

"To date we've managed to eradicate over 20 outbreaks in Sunraysia so it's no time to be complacent."

Mr Ashcroft said residents with fruit trees needed to remain vigilant and pick all fruit before it got too ripe or fell on the ground.

He also encouraged residents to freeze any unwanted fruit before disposing of it.

"You have a responsibility as a resident to look after fruit trees because we're part of an area where there's fruit production," he said.

The DPI also detected fruit fly in Kenley, where the pest was found in a nectarine tree in the home garden of a commercial orchard property.