In New Jersey, where a warm winter caused fruit trees to blossom early, leaving buds that are now threatened by killing frosts, helicopters can help a great deal.

Pilots hover over the fields of fruit trees, such as apple, pear and peach, causing warm air to be pulled down over crops during the night, combating the recent killing frosts. It is a technique being used at a number of Garden State farms, such as Phillips Farms in Holland Township.

"I felt we had such a large area exposed that we had to do whatever we could," said farm owner Marc Phillips. "We built some fires in 2012 during that cold snap, but we weren't able to sustain them on the acreage and in 2012 the crop was light for sure."

The 200-acre Phillips Farms grows various vegetables, herbs and flowers, but it is the 60 acres of peaches, nectarines, apples, pears and plums they have to worry about now, Phillips said.

"It's a lifelong endeavor, the planning, the planting, year after year pruning and cultural work. We take each year at a time," Phillips said. "We have 20-year-old apple trees, and some of the blueberries are 15 years old."

Rutgers Professor Emeritus Win Cowgill of the Snyder Research Farm in Pittstown said a warm winter caused many fruit trees to blossom early. Usually, the trees blossom near the end of the time when killing frosts are more common. In New Jersey, May 15 is usually the date after which frosts do not occur.

The Federal Aviation Administration considers the use of helicopters to prevent frost as a form of approved agricultural aircraft operations, such as spraying for pesticides. The only limitation is that the helicopters cannot fly in densely populated areas.

On Monday, the first of two nights Phillips Farms used a helicopter, Holland Township Police received calls asking why a helicopter was flying over the farm.

"We've been doing this for eight years, mostly in New York state," said Princeton's Platinum Helicopters owner and pilot Evan Van Gilson. "It was not until the last three years that New Jersey has seen frost after the budding season started, so it's a very rare practice."

Serving four farms in the state this year, Van Gilson, who also lives in Holland Township, said he uses different sized helicopters at the farms, including Robinson R22, R44 and R66. Typically they will bring two helicopters and four pilots.

Van Gilson said it was "so cold, so early" on Tuesday that they began working at midnight and finished at 7:30 a.m. at Phillips Farms, and on Wednesday he had helicopters and pilots at three farms.

"We cover more ground, and keep it going steadily," Van Gilson said. "There's a hundred different ways to try and save your crops, but this is proven and tested.

"Some farms already lost more than 50 percent of their crops this year, and they can't afford to lose more."

Jim Peters, an FAA spokesman for the eastern U.S., did not immediately know how common the use of helicopters is in combating frost, but the cost to rent a helicopter for this use ranges from $800 per hour to over $1,000.

Mellick's Town Farms co-owner Peter Mellick said it is highly effective in emergency situations, and they have used helicopters to treat 90 acres of fruit trees at their farms in Lebanon and Tewksbury townships in 2013, 2015 and on Wednesday.

"It only warms them up a few degrees, but that can be the difference between having a crop survive or not," he said.

With the cold weather expected to continue, including the threat of several inches of snow on Saturday, the state Department of Environmental Protection has extended the time when farmers are allowed to use open burning to protect against frost.

Department of Environmental Protection spokesman Bob Considine said in a press release that steps need to be taken to protect the state's fruit crops. New Jersey is among the top states in the nation in blueberry and peach production.

While some farms turn to agricultural tourism to boost revenue, Phillips said they rely on cash crops to survive. "We have pick-your-own events, but that's all we do," Phillips said. "No carnival is going to save us if we don't have fruit."

If the cold weather continues, farms that grow flowers and other later blooming crops may be in trouble too.

"A couple more weeks down the road, and it will be a problem for us," said Renee Bellion of Schaefer Farms in Readington Township. "The flowers at the stand need to harden and get a little wind, but right now everything is in the greenhouse because it's not ready, and if the frost continues we'll be covering them with bed sheets to retain warmth."

Bellion said that vegetables like asparagus and rhubarb are "still sleeping," and although they can sometimes plant sweet corn in early April, the farmers are waiting for the threat of snow to pass.

"When we've had stuff like that with the sweet corn in and a nasty frost snap, we've had to use our sprinkler system, the big gun," she said of an above-ground irrigation system that delivers a constant mist. "If the cold weather continues we would look to that, but it's expensive for electricity and it's an all-nighter."

As for open burns and warm manure, Bellion agreed with Phillips that the practice is difficult to maintain on a large property, and she added that too much nitrogen in manure can chemically burn a plant.