Foamy Bark Canker

Your almond trees are under a new threat.

Branch infected with foamy bark canker (Photo courtesy of Akif Eskalen and Shannon Lynch, CFPC)

In 2015, a new fungal disease of live oaks appeared in southern California. That disease is called foamy bark canker. The fungi responsible, Geosmithia pallida, are transmitted by western oak bark beetles (Pseudopityophthorus pubipennis).

Drought- and water-stressed trees are susceptible to countless pests and diseases. Physical injuries and pest feeding all leave holes in the bark. Healthy trees can protect themselves, but weakened trees cannot.

Western oak bark beetle (Photo courtesy of Akif Eskalen and Shannon Lynch, CFPC)

Western oak bark beetle

This small (2 mm) bark beetle is more of a pest than a threat most of the time. Bark beetles burrow under the bark. These burrows create a gallery of tunnels that cross the wood grain. Female beetles lay their eggs in tiny pockets perpendicular to these tunnels. The larva feed and tunnel their way to adulthood. These pests can certainly weaken a tree, but healthy trees can survive. However, just as elm bark beetles carry the devastating Dutch elm disease, which killed 75-90% of the global elm tree population, this fungal disease threatens almond trees and coastal live oaks.

Symptoms of foamy bark canker

Red, oozing discharges can be seen at beetle feeding sites along the trunk and from primary branches. As the disease progresses, that ooze becomes foamy and prolific. Drips may run down the trunk of an infected tree as much as two feet. If you peel back the bark, you will see that the phloem has died around the entry point. You may also see several entry holes with similar symptoms. Foamy bark canker is easily mistaken for fusarium wilt or shot hole borer, but the entry holes are smaller.

Oak infected with foamy bark canker (Photo courtesy of Akif Eskalen and Shannon Lynch, CFPC)

Tree death caused by foamy bark canker (Photo courtesy of Akif Eskalen and Shannon Lynch, CFPC)

Management of foamy bark canker

Unfortunately, there are no cures for foamy bark canker. The best thing you can do is to keep trees healthy with proper selection, placement, irrigation, pruning, and feeding. Large trees are a long-term investment. They are difficult (and expensive) to replace. During drought, irrigate large trees to a depth of one foot, two or three times a month.

If your tree develops symptoms, contact your local Cooperative Extension Office. With your help, they can document the spread of the disease. They can also provide helpful information.