Chalk up orange juice as another casualty of the war on sugary beverages.

Sales of orange juice, a onetime breakfast staple, have declined precipitously as less-sugary green drinks have taken a big chunk of its shelf space.

“Americans drank less orange juice in 2015 than in any year since Nielsen began collecting data in 2002,” The Wall Street Journal reported earlier this year.

The decline is due mostly to the fact that it's packed with sugar, albeit natural sugar.

PepsiCo, owner of Tropicana, has lined up a marketing campaign to boost the 70-year-old brand with millennials.

The beverage giant this month began buying native advertising space with Ashton Kutcher's “A Plus” digital news site — which espouses positive news — in hopes of making millennials learn to love its OJ. The site has 11.5 million unique monthly visitors, according to a September news release.

The native content series, called “Morning Spark,” includes videos promoting OJ as a feel-good morning beverage and positive way to start the day. Kutcher's pull is helping with his network of celebrities.

The video has been shared on Facebook by Adam Levine, Robin Thicke and Lil Wayne.

Marion Nestle, a professor of nutrition at New York University, has no problem with Pepsi trying to make a 8-ounce glass part of millennials' daily constitutional.

“They are trying to sell orange juice,” Nestle said. “That's their job.”

Although she recommends a real orange over the processed juice, “an 8-ounce glass of orange juice is just fine,” she said. “When I was growing up, we had 6-ounce juice glasses. It took care of your need for really important vitamins.”

Nestle, who is not known for her soft spot when it comes to Big Beverage, gave the Purchase, N.Y.-based food, snack and beverage company a nod. “Pepsi has pledged to put real money into advertising its healthier products. Let's give them credit for doing that in this case.”

Pepsi said OJ is a nutritious eye opener, with vitamin C, essential potassium and folic acid, crucial to women of childbearing age. But David Ludwig, a professor of nutrition at Harvard's T.H. Chan School of Public Health, cautioned consumers before they jump on the orange juice express.

“Fruit juice and whole fruit are not the same,” Ludwig said. “We need to be encouraging whole fruits while limiting consumption of concentrated or processed sugars. And most commercial fruit juices are in that (processed sugars) category.”

“This campaign flies in the face of national recommendations to increase consumption of whole foods and limit highly processed carbohydrates. Commercial fruit juices clearly fall into that second category.”

Why did Pepsi pick millennials?

Upside.

The company's research shows there is tremendous room for growth among the 75 million members in the demographic, which is considered ages 18 through 34.

“Millennials no longer consider OJ a breakfast staple and could really live with or without it,” according to research by the Florida Department of Citrus. “That is why creating an emotional and cultural connection to orange juice is so important to the brand.”

Pepsi is hoping its feel-good campaign creates a connection with OJ.

It's not going to be easy.

“Millennials are obsessed with health,” said Gabrielle Bosche, a strategist who consults with companies on how to reach younger consumers. “Unless it's cold pressed and organic, this generation isn't interested in juice.

“Juice companies that thrive with this generation have packaging that makes it look local, tout the health benefits and understand that it is about what the brand represents, than what the product actually is.”