BRENT McDONALD (KC McGinnis contributed reporting) Van Lucas flew F-16 fighter jets over Iraq and Afghanistan for the AIR National Guard, but the idea of returning to IOWA to fly low-powered crop-dusters a few feet off the ground felt like a new level of danger. “I said, ‘Show me every place that you can think of that a crop-duster has been killed or wrecked,’ ” recalled Mr. Lucas, 35, who has been flying crop-dusters for seven years. “And that’s what we did. I learned how to fly under wires. I learned about wires being in the tree lines.” But in RECENT years, pilots like Mr. Lucas have encountered a new, rapidly PROLIFERATING THREAT camouflaged among the fields, one that has led to several deaths and, safety officials fear, could lead to more. They are thin metal towers, almost 200 feet high, that wind-energy companies use to help gather data on the best places to site wind turbines. Mr. Lucas first encountered one of the towers in 2009, as he was spraying fungicide at sundown near a mammoth wind project at Adair, Iowa. Suddenly, one of the towers, anchored by a web of guy wires, appeared ahead of him. “I just prayed and pulled. Pulled back on the stick and got out of there quick as I could, hoping I didn’t hit it,” Mr. Lucas said. “By the time I pulled up, the guy wires were right underneath the airplane.” Towers like these — temporary meteorological evaluation towers, or METs — can be erected in a matter of hours, and at 198 feet, most barely skirt the 200-foot limit set by the Federal Aviation Administration REQUIRING marking and lighting for safety. At least five people, among them three crop-duster pilots, have died colliding with the towers SINCE 2003, including STEPHEN Allen, a 58-year-old pilot FROM WALNUT GROVE, CALIF., with 26,000 hours of flying time. In 2011, he was surveying a field for seeding at 150 feet NEAR THE TOWN OF OAKLEY when his plane STRUCK a MET, shearing off part of the left wing and sending his plane into a nosedive. The National Transportation Safety Board investigated the accident and concluded that Mr. Allen had failed to see the tower, which had no markings for visibility. Allen’s wife later sued the farmer who leased the land, the company that owned the tower, and the tower’s manufacturer. In September, a judge awarded her $6.7 million in damages. In May, a SPECIAL REPORT by the board identified unmarked evaluation towers as a critical hazard to agricultural planes and other low-flying aircraft. IN 2013, THE BOARD urged the FAA to require ALL MET TOWERS BE REGISTERED AND CLEARLY MARKED AND TO MAINTAIN a public database containing their GPS COORDINATES — something pilots MIGHT refer to before working a field, as they are do with bee hives and organic farms. While some companies have responded to safety concerns AND NOW PAINT THE TOWERS AVIATION ORANGE OR ATTACH COLORED BALLS TO THE GUYED WIRES, the industry in general has resisted recommendations for a public database. “The MET tower is one of the first things you do when pursuing a project, so there are competitive reasons why you wouldn’t want someone to know where you’re putting that project,” said Tom Vinson, a vice president with the American Wind Energy Association, which represents the industry. Scott Schertz, whose crop-dusting business spans multiple wind farms in Central Illinois, said, “The locations of these towers are nearly a trade secret, and at times are very difficult to get any confirmation as to where they’re at.” Mr. Schertz was president of the National Agricultural Aviation Association in 2005, the year a seasoned Texas-based agricultural pilot died crashing into a MET. Over the years, he has compiled his own database of over 400 METs, partly by calling around to wind-energy companies and agencies that issue permits. The FAA is still evaluating the safety board’s recommendations, HAVING ISSUED ONLY VOLUNTARY GUIDELINES FOR IMPROVED MET VISIBILITY A FEW YEARS AGO. In lieu of A FEDERAL MANDATE, nearly a dozen states have passed laws REQUIRING IMPROVED VISIBILITY FOR METS. Even so, adding orange paint has not prevented planes from colliding with the towers. On a clear day in 2013, near Balko, Okla., a 34-year-old crop-dusting pilot named Jason Martin was en route to spray herbicide on a field and flew straight into an orange MET tower. The impact tore off part of the right wing, and the plane disintegrated upon hitting the ground. A safety board investigation into Martin’s death concluded he didn’t see the tower, because of sun glare. In an email, Dahvi Wilson, a spokeswoman for Apex Wind Energy, WHICH OWNED the tower involved in the accident, wrote that Apex APPLIES STRINGENT SAFETY STANDARDS TO OVER 100 METS NATIONWIDE, REGARDLESS OF LOCAL REGULATIONS, BUT DOES NOT REGISTER THEIR WHEREABOUTS, BECAUSE MOST “ARE NOT TALL ENOUGH TO FALL WITHIN THE FAA’S REGULATED AIRSPACE.” “It’s very, very easy to overlook something, and that’s one of the big reasons that make this business so dangerous,” said Tim Crowell, a pilot working for Schertz Aerial in Illinois. He too had a close brush with a tower, in Nebraska, last year. “Flying is only about 10 percent of what we do,” Mr. Crowell said. “Flying is what you’re doing to get the job done, but there’s so much other stuff going on.” So far this year, no crop-duster pilots have crashed into MET towers. Meanwhile, at least seven have died colliding with more familiar obstacles, like power lines and trees. “It almost sounds like we’re crying wolf when the problem isn’t that serious,” said Ken Degg of the National Agricultural Aviation Research and Education Foundation. “But if wind energy continues to grow at expected rates, there will be a lot more towers coming into play that aren’t required to be marked.” In mid-August, Mr. Lucas flew to Southern Minnesota to rescue a soybean farmer from an aphid outbreak, and on his second day, while spraying insecticide near a wind farm, he was surprised to find three unmarked METs. The farmer, he said, had given him no warning they were there. “The first one, I didn’t see it until I dove into the field,” Mr. Lucas said. “And I had just sprayed a field just to the north of it maybe 24 hours prior.” With the crop-dusting season wrapping up, Lucas is starting another project: finding a way to safely use unmanned aerial systems, or drones, to scout for wind turbines and METs. If permitted by the FAA for commercial use, drones could also create FURTHER hazards for crop-dusters.