Stress on hazelnut trees can lead to bacterial blight
By JOHN SCHMITZ
For the Capital Press
While it in no way equals eastern filbert blight in its destructive effect, bacterial blight is a disease hazelnut growers should always be on the lookout for, experts say.
Sometimes called "western filbert blight" to distinguish it from EFB, bacterial blight is especially a problem in young, stressed orchards where trees are 1 to 5 years old. To a much more limited extent it's also been popping up in older orchards, especially those that receive a lot of rain.
"It's a totally different beast (than EFB), a bacterium rather than a fungus," said Oregon State University assistant hazelnut breeder David Smith. "And it's something that's pretty ubiquitous, with certain environmental conditions making it problematic in certain years."
Smith said that he had heard reports that the new OSU variety Jefferson has been more susceptible than other cultivars, such as Lewis. "Lewis has been a variety that has been planted recently, and nobody's mentioned any problems."
Barcelona, Oregon's flagship hazelnut variety, has also been found to be "quite susceptible," Smith said.
"Our message to growers is treat Jefferson the way you would if you were planting new Barcelona orchards," Smith said. "That involves spraying them with copper fungicide in the winter to protect them."
Smith said that the "key" factor that lays a filbert tree open to bacterial blight is stress, "whether it's drought stress, cold stress or heat stress."
"It's really trees five years of age and younger in dryland conditions (that) have more of a problem with that," said OSU plant pathologist Jay Pscheidt. "If we don't have irrigation in those first couple of years we see more of the blight. It will kill young trees down to the ground."
Smith said that bacterial blight is more manageable than EFB.
Some of the symptoms of bacterial blight include yellowing leaves in early summer and limb dieback. While the disease produces cankers, they are not as visible as EFB pustules.
Cankers do not become all that visible until they reach the trunk of larger, older trees, at which time there is some oozing, Pscheidt said.
Pscheidt said that he's seen dieback on whole limbs in trees 10 to 15 years old where bacterial blight gets a foothold. He added that it's rare to see an entire older tree die back.
"It's one of those things that people who have young trees should be watchful for," said Polly Owen, who manages several hazelnut organizations.