The white fluff has fallen.

Actuarial studies and finance student Megan Tran said the saying at the university is: "once the white fluff starts going, you better start studying or you will fail your exams."

"It's one of those superstitions that every uni student goes through," the 21-year-old said.

"It's probably there to scare the first years, but it sticks with you throughout your whole university degree...it's good motivation to kind of get into gear."

Dimity Phillips, a former student and now staff member at the university said the saying has been around for decades.

"It's just part of ANU...it was around when I was a student in 1997. I absolutely believed it," Ms Phillips said.

"It's a good reminder...the lovely weather you kind of relax a little bit and then you kind of get a bit of a kick up the backside to remind you that, 'oh hang on, exams are going to be far closer than we think'."

The fluff is the seed from poplar trees, which have hair to help them loft in the wind, Australian National University professor Geoffrey Hope said.

He said the main contributors on campus are the populus alba [silver poplar] and populus alba pyrimidalis [upright silver poplar].

"These trees are adapted to a short growing season so they flower in very early spring and set seed by early October in order to get their seedlings going before winter returns," Professor Hope said.

"...the fluff appears about two weeks before the end of term. So it is a definite reminder that one should be on top of the subject and getting those pesky end of semester two assignments well underway."

Professor Hope said the fluff should not impact hay fever suffers as it is not allergenic and the particles are too large to get into the nose.

"But it marks a peak season for grass and other pollen which cause a mass of hay fever symptoms."

He said depending on the rainfall, the fluff will fall between two to three weeks.

There are fears the friendly reminder to start staying may disappear with the removal of trees from the centre of the university as part of a $220 million Union Court redevelopment.

"There are lots of them [poplar tree] around where the court is...a lot of them are actually being cut down," Ms Phillips said. "I don't know how much fluff there's going to be in years to come."

But, the university has assured Fairfax Media and their students the trees will be back.

"All trees that are removed will be replaced, so there will be no loss of trees on campus from the building development," a spokesperson said.

"Trees with historic or heritage value will be protected and retained."