WASHINGTON – The swishing of hand-held blueberry rakes wielded by dozens of field workers is being replaced by the rumble of tractors across Maine’s wild blueberry fields as growers turn to mechanical harvesters to pick the lucrative crop.

A decade ago, about 20 percent of Maine’s 60,000 acres of blueberry fields were harvested by mechanical means. Today, it’s about 80 percent as growers discover that it’s cheaper to replace hand pickers with more efficient machinery.

Here on a gently sloping hill off a remote dirt road, two John Deeres move slowly through a field, mechanical contraptions hanging off one side raking the fruit off low-lying bushes. Walter Degreenia drives one of the tractors as his wife, Gail, stands on a back platform sorting through the berries as they are carried on a conveyor belt and dropped into crates.

“On a good day, I can harvest 10,000 pounds with one machine,” Degreenia says.

That’s about 10 times what a typical person can harvest in a day with a hand-held rake, swiping it through the bushes over and over for hours on end.

Maine’s wild blueberry industry, which dates to the 1840s, counted on hand-pickers to get the crop for more than a century – long after growers of other major crops turned to tractors and sophisticated harvesters.

But with the yearly harvest averaging about 70 million pounds a year – up from fewer than 20 million pounds before the 1980s – wild blueberry growers have had a hard time finding enough people to pick all those berries.

Wild blueberries grow naturally in Maine and eastern Canada. They’re different from cultivated berries, which are larger and grow on high bushes.

About 40 percent to 50 percent of cultivated blueberries are hand-picked, but the mechanization trend is happening in the dozen states where they’re grown as well, said Frank Bragg, chief executive officer of the Michigan Blueberry Growers Association.

In the old days, Maine’s blueberries were harvested by local residents, including school kids and American Indians from Maine and eastern Canada.

These days, growers turn mainly to migrant workers from Mexico and Central American countries to fill the void. But with labor in tight supply, growers also have been turning to mechanical harvesters.

“Right now, you can’t even get migrant workers if you want them, so that’s what’s driving this,” said David Yarborough, a blueberry specialist and horticulture professor at the University of Maine.

Maine growers like mechanical harvesters because they don’t have to manage hard-to-find workers and deal with government paperwork. The machines also result in lower production costs – adding to the bottom line.

The early models often destroyed plants and had low yields compared with hand-pickers. But the newer models are efficient with high yields.

And as the machines have improved, the state’s blueberry growers have flattened and removed rocks from thousands of acres of fields to make them suitable for mechanical harvesters.

Nat Lindquist, vice president of operations for Jasper Wyman & Son in Milbridge, said half of his company’s 7,000 acres are harvested mechanically. Some blueberry growers, he said, don’t use hand-rakers at all anymore.

“Over the years, the manufacturers have added more bells and whistles that have improved the quality and are picking most of the fruit,” Lindquist said. “Prior to the improvements, they left a lot of the fruit on the ground.”