Berries attacked by the fungus are called mummies because they look like mummified berries: dried, shriveled and gray-white, instead of plump, juicy and blue.

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EUGENE, Ore. — What Bill and Anita Cook should have been doing once the weather cleared last Wednesday was pruning their 60-year-old Atlantic, Jersey, Dixie and Stanley blueberry bushes — snipping away at older, weaker limbs crowding out the stronger ones as they prepare to bear fruit this summer.

Instead, the Cooks’ eyes are fixed on the muddy ground beneath the bushes on their 1-acre farm in west Eugene. They were preoccupied with a painstaking task: picking up “mummy berries,” one by one, and pocketing them.

This job has become as necessary as pruning because of the growing threat that the mummy berry fungus, Monilinia vaccinii-corymbosi, poses to Northwest blueberry farmers.

With some help from the vinegar fruit flies that found their way to the Willamette Valley a few years back, the fungus has wiped out half of the Cooks’ yield, for two years in a row. Other farms have seen entire blueberry patches devastated.

And because the mummy berry is particularly adept at not just surviving winter but shooting millions of spores that are carried by the winds from one field to the next, every bad year could mean the next one is worse, if the fungus isn’t controlled.

Berries attacked by the fungus are called mummies because they look like mummified berries: dried, shriveled and gray-white, instead of plump, juicy and blue.

The fungus is discovered only at the same time blueberries are nearly ready to harvest, and they look like what they are — duds, ugly useless fruit. It’s after they drop to the ground that they threaten to do the most damage to future crops.

At that point, the mummies act more like zombies. They “overwinter,” lying peacefully in the mud, often obscured by leaves. Come spring, they sprout tiny mushroomlike structures with small cups on the end, called apothecia.

A single cup can produce a million spores in less than a week and can spread to the leaf buds and young shoots of neighboring plants in a matter of hours or days.

Then comes secondary infection, a second kind of spore produced by the infected shoots, called conidia, that moves from blighted shoots to nearby flower blossoms. This spore doesn’t rely on the wind alone for safe transport: rain, bees and other insects can ship it far and wide.

It’s the conidia that germinates with pollen and infects the fruit slowly, as it develops, which is why there’s no way to tell if a bush has mummy berry until its fruit fails to ripen.

“Your crop looks great,” said Jay Pschiedt, a plant pathology professor at Oregon State University. “Right up to harvest.”

The ideal climate for this noxious rite of passage: a cold, wet spring. Local blueberry farmers have seen cold, wet springs the past two years.

The timing is particularly frustrating for Oregon’s 300 growers because the global market is starved for blueberries, which are prized for their antioxidant prowess and flavor.

In 2003, there were 23.5 million pounds harvested statewide. By last year, the number had climbed to 65 million. Acres in production jumped from 2,800 in 2002 to 7,600 in 2011.

Last fall, Oregon became the first state in the nation to gain approval to export its blueberries to South Korea, adding to a long list of countries to which the product is shipped, from Argentina to the United Kingdom.

But blueberries can’t be sold if they are shriveled and gray. And unless all growers dedicate themselves to battling the fungus, they’re all at risk of diminished yields, and profits.

Last year’s production rates were down by about 10 percent statewide, said Bryan Ostlund, administrator of the Oregon Blueberry Commission, although he attributed that decline in part to the cold weather that hampers the berries’ growth.

Therein lies another frustration about the mummy berry: The weapons in a grower’s arsenal are weak, especially for those who want their crops organic.

While commercial fungicides are mostly effective, organic options don’t seem to work all that well, said Ross Penhallegon, Lane County agent for the Oregon State University Extension Service.

“For anybody trying to grow organically, it is a major issue. Every mummified berry that hides in the grass is going to cause a problem,” Penhallegon said. “It is a real threat to the blueberry industry.”

And that’s what reduces Bill and Anita Cook to the mind-numbing task they undertook last week: reaching down to the ground and snatching up one mummy berry after another, by the hundreds.

If the ground were dry, they’d do this with a broom and dustpan. One year, they brought out a Shop-Vac, and they have since upgraded to a more industrial machine. But none of those options works in the mud.

The Cooks have tried lime sulfur, raking and some combination of spraying, organic and otherwise. When all that failed, they returned to the approach that’s hardest on the back and knees: picking them all up.

Then, the mummies go straight to the dump.

“I have taken a torch to them,” Anita Cook said. “They don’t burn.”