Crews are treating ash trees in Indianapolis' city parks to combat the spread of the tree-killing emerald ash borer.The city's Department of Public Works says this is the third year of a five-year program called the Legacy Tree Project designed to raise public awareness about the invasive bug.About 200 ash trees in three city parks are being treated with an insecticide proven to protect ash trees from the destructive insect.Plant healthcare technician Brian Fannin said he injects insecticide directly into the soil surrounding trees to combat the beetles."The treatment methods are very important on a proactive basis to get ahead of the game," Fannin said.Noblesville City Arborist Paul Lindeman also took proactive steps to fight off the pests, RTV6's Derrik Thomas reported."Treat the trees before they are infected. We do know in Hamilton County we have areas around us that have been hit already. Eventually, it will move in and encroach on the Noblesville area," Lindeman said.Homeowner Janelle Keller said her street is lined with ash trees."They are such beautiful trees. It would be such a huge disadvantage, I think. That's all we have along the street. That would be pretty devastating," Keller said.The small, metallic-green beetle that's native to Asia has decimated ash trees in several states since 2002. The emerald ash borer has already destroyed trees in 51 Indiana counties.