Posts Tagged: Canker

Decline of coast live oak trees in S. California is due to fungus

A fungus associated with the western oak bark beetle is causing a decline in coast live oak trees in Southern California by spreading “foamy bark canker disease.”

“We have found declining coast live oak trees throughout urban landscapes in Los Angeles, Orange, Riverside, Santa Barbara, Ventura and Monterey counties,” said Akif Eskalen, UC Cooperative Extension specialist in the Department of Plant Pathology and Microbiology at the University of California, Riverside.

Eskalen recovered the fungal species, Geosmithia pallida, from tissues of infected coast live oak trees and performed pathogenicity tests on it in his laboratory at UC Riverside.  The tests showed that the fungus is pathogenic to coast live oak seedlings and produces symptoms of foamy canker.

The western oak bark beetle, which spreads the fungus, is a small beetle — about 2 millimeters long — that burrows through the bark of the coast live oak tree, excavating shallow tunnels under the bark across the grain of wood. Brown in color, this beetle is native to California. Female beetles lay their eggs in the tunnels.  It is not known at this time if the beetle infects trees other than coast live oak trees.

Symptoms of foamy bark canker disease include wet discoloration on the trunk and main branches of the infected coast live oak tree.  This discoloration surrounds the entry holes that the western oak bark beetle makes to burrow into the tree. Multiple holes can often be seen on an infected tree.

“When you peel back the outer bark of the infected area, you see bark (phloem) necrosis surrounding the entry hole,” Eskalen said. “As the disease advances, a reddish sap may be seen oozing from the entry hole, followed by a prolific foamy liquid.  This foamy liquid, the cause of which remains unknown, may run as far as two feet down the trunk.”

Eskalen explained that when the infection is at an advanced stage, the coast live oak tree dies.  Currently, no control methods are in place to control the fungus or the beetle.

If you suspect your coast live oak tree has the symptoms described above, please contact your local UC Cooperative Extension advisor, pest control adviser, county agricultural commissioner's office or Eskalen at akif.eskalen@ucr.edu.

To see more photos, visit http://ucrtoday.ucr.edu/22096. 

California farms grow pumpkins for fun, not profit

California is the nation's No. 2 pumpkin producer, but the crop is unusual among the state's agricultural commodities, according to an article in the Los Angeles Times by Diana Marcum. Pumpkin farms tend to be small and most pumpkins are sold directly to consumers by farmers at roadside stands or U-pick operations. California pumpkins are more commonly used for jack-o'-lanterns than pie filling.

"Pumpkins are really different," said Tom Turini, a farm advisor with the University of California Cooperative Extension in Fresno. "We're not trying to feed the world pumpkins. It's more about tradition, family. It's farmers just having a little fun."

Fungal Killer of Cypresses Originated in California
John Upton, New York Times

Last month, scientists from UC Berkeley and the National Research Council in Italy reported that they traced Seiridium, the fungus that causes cypress canker disease, back to Monterey cypresses in California. The fungus has caused a deadly epidemic in the world’s forests.

According to the article, Matteo Garbelotto, a forest pathologist at Berkeley and a member of the team of scientists, said that the problem began roughly a century ago when landowners started planting Monterey cypress trees in the California Central Valley and in Europe. Outside of their natural environment, they became weakened and more susceptible to infection. As the trees’ immune systems grew weaker, the fungus grew stronger, until it prevailed.

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