New Jersey blueberry farmers have been losing sleep over a nighttime freeze this week and the threat of more sub-freezing temperatures this coming weekend. Blueberry and apple growers have witnessed a roller-coaster ride of nighttime temperatures for the past few weeks. And it is not over yet.

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The unusually warm temperatures at the end of winter and recent cold nights could lead to "some damage," state Assistant Secretary of Agriculture Al Murray said.

A lot is at stake. New Jersey is fourth in the nation in blueberry production, roughly 65-million pounds of blueberries with an estimated value of $80 million annually.

Hammonton, billed as the "Blueberry Capitol of the World," recorded some temperatures under 22 degrees Tuesday into Wednesday of this week.

"A blueberry plant in the bud stage or the bloom stage, which New Jersey blueberry plants are in right now, will sustain damage if temperatures go below 24 degrees for more than four hours," he said.

Murray says blueberry farms that are in low-lying areas typically will experience more damage than in areas where they get a good wind flow or good air currents that will help mitigate some of the freeze.

New Jersey Farm Bureau spokesman Tom Beaver says farmers can use "smudge pots," heaters that burn oil, to warm the berries, but there are no guarantees.

"We are certainly keeping our fingers crossed. We are certainly trying to be cautiously optimistic," he said.

The state Department of Environmental Protection on Wednesday extended their permissions to farmers in the state to use smudge pots beyond April 5 for blueberry, apple and peach crop protection. Beaver says a lot of blueberry growers have moved to "drip irrigation" so they do not necessarily have overhead watering at their disposal. But those are some of the tools that could be used to try to stave off damage.

According to Beaver, the early and midseason varieties of blueberries are the most susceptible right now.

"Later season varieties, they are not as far along in their phase of development, so they are probably not as sensitive to these extreme cold temperatures," he said.