If your orchard had fire blight strikes last year in your apple or pear orchards, now is a crucial time to look for and remove fire blight cankers. Tianna DuPont, Washington State University Extension Tree Fruit Specialist, suggests you use the time before spring to take a closer look at your orchard. Bacteria that survived the winter will be your orchard’s source of inoculum this year.
“Cells of the Erwinia pathogen survive primarily in the canker margins where diseased bark tissue meets healthy bark tissue,” she writes. “Frequently, the pathogen inside many of these cankers dies out over the course of the winter, but in 20% to 50% of cankers, the active cells of the pathogen survive until the next bloom period.”
DuPont says it’s best to remove cankers before winter pruning.
“Compared to cuts made in summer, winter removal cuts can be made closer to the visible canker edge because the pathogen is confined to the cankered area. Cut at the next “horticulturally sensible” site below the canker,” she writes.
As far as location, DuPont says your focus should be in the blocks that had fire blight strikes last year, but “after a year like this one it is best to check all of your blocks.”