A culmination of factors has led to a dramatic year-on-year production decline for wild blueberry production in the U.S. state of Maine this season. 

University of Maine horticulture professor David Yarborough said an average of around 100 million pounds had been produced annually over the last three years, but he speculated the figure would drop to about 65 million pounds this season.

The harvests are expected to wrap up this week, he told Fresh Fruit Portal. Picking usually begins around the end of July but started a little later this year.

He explained there were four key factors behind the significant drop in volumes this season.

"We came into the spring with a good potential for a normal crop, but we have very wet, cold and windy weather during our pollination period," he said.

On top of that, poor returns over the last couple of years on the back of high North American blueberry production led to less investment in pollinator hives brought in from other U.S. states and Canada.

"Two years ago we probably had 77,000 hives come into Maine, the year before was 58,000 and this year it was 27,000. So there's been a significant reduction in pollinators," he said.

He explained much of the fruit produced this year was much smaller as a result, with per-acre yields far lower than normal.

Another factor was the prevalence of "mummy berry" disease, a fungal pathogen that became more prevalent due to wet spring weather. 

The other reason Yarborough gave for the decline was a lack of rainfall during the key growing period after spring.

"Up to July there was adequate rain, it looked like we might have recovered, but into July and August there was a great deficit. It was the final nail in the coffin," he said.

A limited proportion of the wild blueberry fields are irrigated, he added, allowing some growers to achieve 7,000 or 8,000 pounds per acre, compared to the typical 5,000 pounds.

Maine traditionally produces around 10% of the U.S. and Canadian blueberry production - both wild and cultivated - with 99% of the crop sold on the frozen market.

Yarborough said there were hopes that the lower crop would translate into improved prices for growers, who have seen their profits slide over recent years due to supplies on the frozen market outpacing demand.

"Over the last three years there's been a significant increase in storage," he said.

He that as frozen blueberries could keep well for at least a couple of years, growers could wait in the hope that prices would come back up. But he pointed out this would mean higher costs for storage.

"I would expect given time the price would come back up, but that depends on demand," he said.

"If we have some more short crops and we continue that demand curve up we can get back to being profitable again."

Wild blueberries are grown on 44,000 acres in Maine. These fields have been developed from native plants that occur naturally in the understory of the forest but are managed by growers.

Because of the pruning practices employed, only half of the acres are available to be harvested every year

Yarborough said increased management over the years had led average production to increase from 20 million pounds to 100 million pounds a year despite a decrease in acreage.

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