Helicopters to save crops

Dozens of helicopters are whirring above Florida's valuable and sensitive veggie crops, an unusual approach by farmers worried that an uncommon freeze could wipe out their harvests. They hover low over green bean and sweet corn fields, moving back and forth in the early morning hours to push warmer air closer to the plants, and, the farmers hope, save plants from a deadly frost.

Farmers are especially nervous because the 11-day freeze in January wiped out many crops, from corn to kumquats. Florida is the largest winter producer of sweet corn in the U.S., the kind people eat.

The stakes are high — in 2009, the value of production of sweet corn from Florida was $227 million.

“They have hundreds of thousands, millions of dollars in crops,” said Paul Allen, president of the Florida Sweet Corn Exchange.

The helicopters may be the last line of defence if temperatures dip below freezing, as expected, though it is an expensive technique. It costs about $2,500 an hour to fly one helicopter over the crops, and the length of flights depends on a mix of temperatures and wind conditions.

Here's how it works — the air 50 feet (15 m) above the crops is warmer than the air near the plants. The helicopter blades push the warm air down and the temperature goes up, said David Sui, a University of Florida expert on vegetables and tropical fruits. The warmer air prevents cold and frost from settling on the plants. “Even if it raises the temperature a couple of degrees it may save the crops.” he said.

The technique isn't a new one, as it has been done before. Strawberry farmers are spraying water on the plants, so the heat lost from the crop to the surrounding air is replaced with the heat released as water changes to ice. Citrus farmers are using ground-level heaters to warm the air near tree trunks. And tropical fish farmers are moving their fish or covering outdoor tanks. January's cold snap damaged large swathes of strawberries and tomatoes. Nearly all of the kumquat crop died.

When Florida's crops die, shoppers pay more at the grocery store because replacement produce is usually imported from outside the U.S.— AP