INDIANAPOLIS (AP) — Indiana's drought is stressing the state's trees, leaving some prone to diseases and insect infestations and killing others outright as the hot, dry conditions linger.

In Indianapolis, about 80 teenagers who had been hired by Keep Indianapolis Beautiful Inc. to plant trees this year are instead working to save trees planted in previous years by regularly watering them.

The teens are watering about 5,000 trees each week in city parks and greenways using 500-gallon tanks moved around in horse trailers.

Keep Indianapolis Beautiful President David Forsell told The Indianapolis Star (http://indy.st/PzBzVF ) for a story published Monday that adults are pitching in as well, but more volunteers are needed in the tree-watering campaign.

"We're working them harder than in years past. This is urgent action for the long view," he said.

Forecasters say Indiana's worst drought in decades may linger into this fall and Forsell said the full impact of the drought on trees may not be known for months or longer.

"Sometimes, large trees take several years to show the stress of what they've gone through," he said.

Courtney Stellhorn, a commercial horticulturist with Dammann's Lawn Garden & Landscaping Centers, said some trees are so water-starved they're dying.

"I've seen mature trees dying — 40-year-old white pines, spruces, even willows around retention ponds. Anywhere around the city you see this death," she said.

Dammann's staff has been busy watering the more than 500 trees in its inventory, among them maples, Japanese maples, oaks, willows, fruit trees, evergreens, hemlocks.

"Job one right now is to keep things alive," Stellhorn said.

Susan Stilz, a Damman's greenhouse supervisor, said the garden and landscape company is urging people to think twice about buying trees right now because new trees would face "an enormous struggle to get established."

Purdue Extension urban forestry specialist Lindsey Purcell said trees across Indiana and the Midwest are struggling in the arid conditions and some could succumb or suffer for years to come.

He said droughts weaken trees' ability to withstand insects and diseases by leaving them unable to produce the usual levels of carbohydrates, significantly lowering its energy reserves. Those reserves are needed for a tree to produce chemicals that ward off pathogens.

Purcell said watering trees of any size and age can minimize drought damage, especially for newly planted or recently established trees.