Almond growers watch for fungus that can topple trees

The almond industry has a scary new threat: a mystery fungus that devours trees from the inside out, causing them to snap and fall over.

The fungus is incurable, researchers say.

Scientists say the wood rot fungus typically attacks older fruit and nut trees, but is being found in much younger trees in the San Joaquin Valley.

University of California researchers say the fungus, which belongs to the genus Ganoderma, is no stranger to agriculture and probably is the reason why most trees blow over.

But what is puzzling experts is why it seems to be showing up in greater numbers and in younger trees.

The disease slowly eats at a tree’s heartwood until it becomes unstable and eventually topples. In many cases it can take years for the fungus to bring an older tree down.

But UC graduate student Bob Johnson, who is studying the fungus as part of his doctoral thesis, found thousands of infected trees in a Hanford almond orchard that were just 9 and 10 years old.

“It was so bad you could push the tree over and it would fall,” Johnson said. “The trunk broke off right at the soil. It was unbelievable.”

Statewide, almonds are a $5 billion crop. About a third of production comes from Merced, Stanislaus and San Joaquin counties.

The fungus is “not really anything new,” said Roger Duncan, a farm adviser for the UC Cooperative Extension in Stanislaus. It is one of the reasons why orchards need to be replaced every 25 years or so, he said.

Johnson said the Hanford grower chose to remove all the trees in the 120-acre orchard. Ganoderma also has been found in numerous trees in two orchards within a mile of each other in west Fresno County. And he has received phone calls from growers in Kern, Tulare and Madera counties with concerns about falling trees.

“It is a little early to say how big of a threat this might be,” said Tom Rogers, a Madera County almond farmer. “But it does raise a lot of questions, like how did it get started, and how was it brought in, is it something in the field?”

The fungus damages a tree by slowly attacking its root structure. The tree often looks normal and can even produce a crop. The only telltale sign that the fungus has colonized a tree is the appearance of a mushroomlike growth, called a conk, that sprouts at the base of the tree.

The disease spreads to other trees as the conk releases trillions of spores into the air.

Mae Culumber, a UC adviser in Fresno County, said the fungus has no known cure. And there are few, if any, preventive measures. She tells growers to try to keep their trees as free from injury as possible. The spores infect a tree by entering any opening in the tree’s bark or roots.

This story was originally published February 16, 2017 at 3:52 PM with the headline "Almond growers watch for fungus that can topple trees."