Pest Attacks Dry Eucalyptus

A persistent pest that saps the life out of eucalyptus trees is becoming a major problem in Ventura County as the drought continues, tree experts say.

The culprit’s name is the longhorn borer beetle, and Jim Downer, a landscape adviser at the University of California Cooperative Extension, said this week it has chewed its way north from other parts of Southern California to kill the tall, sprawling trees in Ventura.

“It’s all over the county,” Downer said. “It started in Orange County, it’s been wiping out trees in Los Angeles County, San Bernardino, San Diego, and it’s now in Ventura and Santa Barbara.

“This is a natural pest of eucalyptus that has no natural enemy in California,” he added.

Though tree specialists say the beetle has been present in some parts of Ventura County, such as Simi Valley, for at least three years, it did not appear to be spreading rapidly. But the combination of ongoing drought and the beetle has been more deadly to eucalyptus over the last year, they say. The parasite was first reported in Southern California in 1984 in wood that had been shipped from Australia to an El Toro lumberyard.

Downer, who has been monitoring the pest but says no count has been made of the number of eucalyptus trees killed, said he had come across more beetle-caused deaths of eucalyptus “in the last six months.

“If it weren’t for the drought, it probably would not be getting as many trees as it is,” he said. “Trees that are experiencing drought intensifies the attraction of this beetle.”

When the weather gets hot, the beetle could kill more eucalyptus, said Jim Hughes, retail manager at Baron Brothers of Camarillo. “You don’t see so much of it in cold weather, but as it warms up, you’ll see it more.”

One recent morning, Don Schwabauer could see the effect of the pest in several places on the citrus ranch he operates in Moorpark. Almost every grove and pasture on the 700-acre ranch was bordered with towering rows of tall, gray-trunked eucalyptus.

The trees are important both for erosion control and as a “windbreak,” Schwabauer said, and the fact that several had been dying was troubling him.

“It’s a real concern,” he said. “We get so much wind. We receive tremendous Santa Anas. They protect the citrus trees.”

But, he added, “We’ve lost quite a few.”

Looking at his trees, Schwabauer said, he was convinced that the beetles focused on trees that lacked water. He pointed to one nearby stretch of several dozen trees standing like tall sentinels beside a grove of short, bushy orange trees laden with fruit. “Those trees look fine,” he said.

But they stood next to a well-irrigated grove, he noted, and then pointed to another row of eucalyptus. This one stood between the road passing the property and an empty field of pale, dry earth. Nearly half of those trees were dead.

“We pulled all this grove out because we’ll be replanting lemons this month,” Schwabauer said. “We aren’t irrigating here, and those trees have the beetle.”

Downer drove to some places in Ojai on a recent afternoon where trees had been infected by the beetle. These trees were dead and had lost their color, but their leaves had remained on the branches.

That is the signature of the longhorn borer, Downer said. “Usually when a tree declines, leaves fall. The main thing about the eucalyptus borer is that the leaves stay on the tree. They don’t fall off.”

After a beetle lays eggs in a eucalyptus tree, Downer said, larvae hatch and then tunnel through the tree’s cambium layer, between the bark and the wood, that carries essential nutrients and fluids up and down the tree. The larvae block that flow of nourishment, he added, killing parts or all of the tree. The larvae then bore into the trunk and after several days, emerge through what Downer called an “exit hole,” as a beetle ready for a new attack.

So far there is no known cure for the beetle. “Some pesticides have been tried, but they are not effective,” Downer said.

Tim Paine, an assistant professor of entomology at UC Riverside, said an effort in Riverside about two years ago to introduce wasps from Australia, which are natural predators against the longhorn borer, “did not appear to be successful.”

The best offense, Paine said, is adequate watering, even though that could be a problem in Ventura with increasing limitations on water usage.

“Until we had the eucalyptus beetle in Southern California, people considered them naturally maintenance-free, and felt they didn’t need to water them,” Paine said. “Then people started to take care of them, and we don’t see as much mortality in Orange County, San Diego and Los Angeles. This will probably be repeated in Ventura, now that it’s moving its way north.”

Affected branches or dead trees need to be removed to keep the borer beetle from spreading, Jerry Revard, city of Ventura arborist, said. He removed a large branch that showed signs of the pest from a tree bordering the Santa Paula Freeway about eight months ago, he said, adding, “so far, I haven’t seen any more.” Revard said he encased the diseased branch in tarpaulin.

“If people find evidence of the beetle, bury it, burn it or cover it up with tarpaulin for a year,” he said, “to make sure they are trapped, to keep the population from spreading.”