The Long Fight to Stop Fire Blight

This picture was taken from a commercial orchard in Southern Oregon in 2018 when fire blight was severe in the entire PNW due to favorable weather conditions.  Photo: Kate Lundquist

At the Plant Pathology lab at Southern Oregon Research and Extension Center (SOREC) a very old fight against Erwinia amylovora continues. The disease, also known as fire blight, affects pears and apples, and can wipe out entire orchards. As Dr. Achala KC explains, “fire blight is one of the first bacteria proven to be a plant pathogen. It’s very old, and still even today we don’t have a singular intervention that can solve the issue of fire blight infection. We’re still discovering parts of the whole system of infection and developing interventions and ways to manage orchards once infected to save trees and prevent further infection.”

As the lead PI at the Plant Pathology lab, Dr. KC’s research focuses on pests and diseases that affect economically important crops for Southern Oregon, primarily pears and wine grapes. With a recent award from the USDA’s Specialty Crop Research Initiative (SCRI), Dr. KC is gearing up for another 4 years of studying fire blight and its effects on pear trees from root to blossom. This latest research project is part of a national coalition of researchers all looking at ways to stop the spread of fire blight and arm growers with tools to fight everything from reduced crop outputs to the staggering loss of entire orchards.

“Every year when the weather warms up, new infections happen and can represent acres and acres of tree losses for growers.” Dr. KC explains. The scope of the impact the bacteria has is in part down to the systemic nature of the infection. Fire blight has different stages at which it can infect a tree, and each stage is important for managing the bacterial infection. Whether it’s stopping a new tree from becoming infected or stopping an infected tree from becoming a reservoir for transmission. Once fire blight has infected a tree and made its way to the permanent structure, usually in the trunk, it will overwinter. It doesn’t die off. When spring arrives and the weather warms up again, the cankers on the trunks ooze, and via insect activity and rainy spring weather fire blight infects new blossoms starting the infection process all over again.

While there have been interventions to treat fire blight from spreading to new blossoms, treatment focused on the canker stage is less robust. “Really the knowledge gap was ‘how can we minimize the canker, or even if there is a canker, how can we keep bacteria from being able to reinfect” says Dr. KC. Her research funded by the USDA SCRI grant focuses on that knowledge gap. Working with researchers at universities like Virginia Tech and University of Virginia, Dr. KC provides real-world testing of interventions like the use of UGVs and AI technology to map and identify infected trees for canker removal to new enzymes targeting the fire blight bacteria at both canker and blossom stages.

“One of the most exciting parts of being at a research station is the direct connection with the growers.” says Dr. KC. “The applied aspect of disease management where we really get to understand what the growers are facing and what we can do to minimize that.” That outreach grounds the research. Beyond the orchards at SOREC, Dr. KC works with area growers to identify the scalability of interventions given how they already manage their orchards, and to hear whether a new intervention is working once deployed under commercial conditions.

“I find being a resource for growers and sharing out research results around disease and pest issues growers are facing to be really rewarding.” Dr. KC says. Along with her team of a Faculty Research Assistant, Joseph DeShields, and undergraduate and graduate assistants from Rogue Community College, Southern Oregon University, and Oregon State University, Dr. KC is hopeful that more research focused on reducing transmission from fire blight cankers will prove fruitful. “They really deserve a lot of the credit for the success of our research.” she says with a smile about her team.

Figure 1: Initial phase of Erwinia amylovora infection on pear blossoms.

Figure 2: Blossom blight phase where the infected blossoms are killed and more bacteria are produced as the creamy oozes (red arrow) when weather warms up. These oozes provide more source of bacteria for newer infections of the nearby tissues.

Figure 3a: The blight extends to the permanent tissues and cause cankers. Notice the tree death originating from the canker.

Figure 3b: The cankers eventually kill the entire tree. Notice the tree death originating from the canker.

Figure 4: The entire tree needs to be cut down under the severe case of fire blight infection. This picture was taken from a commercial orchard in Southern Oregon in 2018 when fire blight was severe in the entire PNW due to favorable weather conditions.  This is one of the ultimate solutions to limit the spread of bacteria to nearby healthy trees from severely infected trees.

Figure 5: Part of a research project that Dr. KC is leading on managing fire blight cankers at SOREC pear research orchard.