CENTRAL POINT, Ore. — Srdjan Acimovic lopped off a tree branch loaded with Bartlett pears and told growers and researchers it was painful but necessary.

“This hurts you, right? You’re throwing away five to six pounds of pears,” said Acimovic, a Virginia Tech University assistant professor.

The alternative, however, is having fire blight in orchards for 10 to 15 years, he said.

Acimovic advocated for aggressive pruning of fire blight cankers during the annual Pear Field Day at Oregon State University’s Southern Oregon Research and Extension Center on July 18.

“With pear, you cannot go wrong if you prune hard as soon as you see symptoms,” he said.

Dense orchards spread problem

Fire blight is caused by bacteria and can destroy yield and kill apple and pear trees, especially juvenile trees.

Pears are much more vulnerable to the disease.

“I like to call pear trees ‘lollipops’ for fire blight,” Acimovic said.

Growers should consider the disease the top production problem, he said.

“Once it moves in, it’s very, very, very, very difficult to get rid of,” he said.

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Acimovic said it was crucial to prevent fire blight from spreading from shoots and branches to the trunk because that can kill trees or lead to permanent hot spots in orchards.

Growers moving to high density orchards has helped spread the disease.

Bacteria move through orchards easier with tighter plantings and to trunks faster with shorter branches.

Once farmers get about 40% of trees infected, they’ll pull out orchards that had an initial investment up to $25,000 per acre, Acimovic said.

Combating fire blight

Acimovic told growers that pruning should be done during dry, cool days, as even dew can transport fire blight on shoes.

Growers should drop brush on the ground and let it dry for two to three weeks before picking it up.

Disinfecting tools regularly during pruning also limits infections.

Growers can combat the problem by spraying antibiotics before infections occur during bloom — pollinators spread fire blight — as well as reducing irrigation to reduce susceptibility of trees when symptoms are present.

Researchers are studying applications to limit blight and control cankers, including the use of copper with a mix of bark oils to reduce bacteria populations during dormancy, and whether trees’ immune systems can be boosted as a preventive measure.

Antibiotics should be avoided for shoot blight control because other bacteria develop resistance.

Researchers also are investigating whether artificial intelligence can use cameras to detect fire blight cankers during dormancy. Automated inspection would benefit larger growers.

Farmer response

Juan Quirarte, orchard manager for Naumes Inc., a Southern Oregon grower and packer with 1,300 acres of pears, said he’d be even more aggressive with pruning techniques than Acimovic.

“It kills a lot of trees,” Quirarte said.

“You see it, you have to eradicate it. Otherwise it’s going to spread,” added Cody Bass, Naumes director of food safety.

About 30 people attended OSU’s Pear Field Day, which also included a sterile insect release via drone for coddling moth management by M3 Agriculture Technologies.

The integrated pest management technique currently costs $450 per acre. Nathan Moses-Gonzales, M3 CEO, said that should drop as technologies improve and usage becomes more widespread.

Nancy Vaughn, who has 22 acres of pears near Jacksonville, Ore., said she doesn’t have much fire blight problems compared to other orchards, in part because she’s surrounded by field crops and grapes.

But she still appreciated the Pear Field Day to stay informed.

Her second career is agriculture, and Vaughn said her business wouldn’t have succeeded without OSU’s Southern Oregon Research and Extension Center.