Pie makers are being encouraged to stock up on canned pumpkin for the holidays - an unusually wet June has cut yields of the autumn favorite by about half, according to the main U.S. supplier.

"It would be wise to buy it for Thanksgiving now," said Roz O'Hearn, a spokeswoman for Nestle USA, owner of Libby's, which produces most of the country's canned pumpkin.

O'Hearn said that the pumpkin harvest usually runs from the end of August into early November, but this year it ended on Tuesday.

O'Hearn said Libby's will ship the last of its canned pumpkin to retailers in early November, but will not have any more to ship until the 2016 harvest.

About 90 percent of the canning pumpkin in the United States comes from Illinois. The majority comes from the area around Morton, which calls itself the "pumpkin capital of the world" and is located about 160 miles south of Chicago.

The shortage is related both to heavy rains early in the season and the moisture-related diseases phytophthora blight and downy mildew, according to Mohammad Babadoost, a professor in the University of Illinois Department of Crop Sciences. He said jack-o-lantern pumpkins were also affected, but not as severely as pie pumpkins.

"Some of what we put in just got drowned out," said Morton pumpkin farmer John Ackerman. "Pumpkins don't like to have their feet wet."

He said his ornamental pumpkins, gourds and squash did better than canning pumpkins, because of the diversity of the crop and staggered planting times.

O'Hearn said 2009 was also a tough pumpkin year, due to late rains during the harvest, which stuck tractors in the mud. She said people bought canned pumpkin "aggressively" that fall, and she later saw cans being offered for high prices online.

Ackerman said he has been farming pumpkins since the 1980s, and he has never had a year like this one.

"I'm hoping I don't have another one," he said.