Fire blight killing Petaluma fruit trees

Extremely dry grass and high fire danger aren’t the only impacts of the current drought. The parched conditions are also taking a toll on Petaluma’s fruit tree population as evidenced by an outbreak of the fire blight disease, which some say is the worst seen in Sonoma County in years.

“Fire blight has been going on for quite a few years around here, but it’s been particularly bad this year because of the drought,” said Suzanne Clark, a Petaluma resident and a Sonoma County Master Gardener. “Lack of water weakens the tree and stresses it, allowing for it to be affected more easily to blights and pathogens.”

Fire blight is a disease caused by the bacterium Erwinia amylovora. According to the University of California Statewide Integrated Pest Management Program, fire blight is common in pomme fruit trees and related plants, particularly pear and apple trees.

The name fire blight comes from how the disease gives a brown or blackened, burnt appearance to fruit, leaves and even branches of affected trees. It’s highly contagious. Rain can spread it to other parts of the tree. Infected leaves and blossoms, as well as bees and other insects, can spread fire blight to other trees. Even uncleaned pruning tools have the potential to spread it.

Clark, who lives near downtown, is one of a handful of residents with trees infected by fire blight. Her neighbor has a large Bradford pear with a lot of branches blackening from the disease. She believes that tree has spread the infection to her Arbutus unedo and Arbutus marina, which are members of the madrone tree family.

“I had a branch on the Arbutus unedo that turned black last year,” said Clark. “I cut if off and at the time didn’t know what it was. This year, I’ve lost a few more branches from those trees. I’m concerned my other trees will be affected. I have a new apple tree I planted when I didn’t know about the fire blight. I’m afraid it might get it.”

Rebecca Kagin, who lives in the Paula Lane area, noticed fire blight on her Bartlett pear and Asian pear trees in late May. She’s been pruning off the affected branches in an effort to keep the infection at bay.

“Both trees are still alive and have a lot of fruit,” said Kagin. “It’s a little scary. I understand fire blight can be hard to deal with.”

Dylan Bartley, who lives in the midtown area of Petaluma, noted on the website NextDoor.com that he recently lost a pear tree to fire blight.

Ellen Solomon, a certified arborist who worked as orchard manager at Petaluma Bounty, said that the bounty farm lost two pear trees to fire blight last year, and the battle to stop its spread continues.

“We’re trying to cut out the fire blight. The ones that have it the worst are the Seckel and Bartlett, pears,” said Solomon. “The ones we lost were Comice pears. We had to butcher those trees. It was hard.”

Solomon has also identified some ornamental pear trees on the Santa Rosa Junior College’s Petaluma campus that she said are showing signs of fire blight.

“The infection in those trees doesn’t look too severe, but it’s the kind of thing where if you don’t cut it out, it gets worse and you could lose the tree,” she said. “Last year was a bad year for fire blight, but this year is worse. I have been seeing it mostly on pear trees all over the county, but apples are susceptible to it, too. If you have poor conditions, your trees are more likely to succumb.”

Clark has also noticed fire blight on some trees on Western Avenue, Fourth Street and Fifth Street.

“Trees, like any other kind of plant, need to be maintained,” said Clark, who recently joined the Petaluma Tree Advisory Committee. “Water is essential, as well as compost and proper pruning. If fire blight is caught in its early stages, it can be dealt with.”

The issue of fire blight’s spread through the city was brought up by Clark at the July meeting of the Petaluma Tree Advisory Committee. The committee will officially discuss the topic and a possible plan of action at its Aug. 19 meeting.

“The committee would like to find ways to educate the public about this and other tree topics and issues,” said Ron DeNicola, certified arborist and committee member.

According to DeNicola, the disease has been around for many years, especially in the Petaluma area due to climate. The June rain and warm weather provided perfect conditions for fire blight to spread. An additional problem, he said, is the number of highly susceptible ornamental pears planted around town that aide in the spread of fire blight.

“About 30 years ago, ornamental pear trees were popular to plant in urban areas, so now we have lots of them everywhere,” said DeNicola. “There are infected ornamental pear trees all over Petaluma. If you look out on the median strip of Sonoma Mountain Parkway, most of those trees are ornamental pears and they are all in really bad shape. They’ve been that way for many years.”

DeNicola added that he’s currently looking for a grant for a tree replacement program, but until then, there’s not much that can be done. He warned that controlling the spread of fire blight in Petaluma would be very difficult, simply because of how highly contagious it is and how aggressive the pruning needs to be in order to cut out the infection. He recommends replacing infected and susceptible trees with other tree species that are more resistant to the disease.

“The best thing to do is not plant the species,” said DeNicola. “We don’t plant bay trees anymore because they are the nurturing site for sudden oak death. We don’t plant Monterey pines because of the pine pitch canker problem all over the state. My suggestion is to remove it and replace it with a different species.”

Solomon added that the most important thing tree owners can do is make sure they properly care for their trees, which means giving them appropriate water, mulch and fertilizer. The healthier the tree, the more likely it can fight off disease.

Branches and leaves infected with fire blight must be pruned back and the tools used must be disinfected with each cut to avoid the spread of the disease.

“You can use dormant spray, which is a copper, sulphate mix you spray on trees when they lose their leaves and go dormant,” said Solomon. “It’s a general disinfectant that’s good for a lot of things. It’s no guarantee at all, but it may help. Giving trees the best cultural care to keep them healthy, however, is the best defense.”

(Contact Yovanna Bieberich at yovanna.bieberich@arguscourier.com. On Twitter at Yovanna_Argus.)