For a long time, my family members have talked about the uncertainties of agriculture. You can do everything right and then nature throws a curveball. You figure out what happened then pick yourself up and try again.
Last winter, nature pitched three curveballs in the Civic Center Apricot Orchard. Although there was a short freeze, the total chill hours were less than expected. That was a one-two punch for the dormant buds on small trees. Then the late spring rainstorm battered the newly emerging buds. These were perfect conditions for infection with Bacterial Canker.
Our orchardist, Terence Welch, walked the orchard with Andy Mariani in March to seek a second opinion. They noted that 301 out of 393 trees appeared healthy with new leaves and tiny fruit. Then there were the small trees with bare branches, shrivelled blossoms and a few shrivelled leaves. Suckers sprouted from the rootstock below the graft on some of these small trees in poor condition. Andy took out his pocket knife and sliced a small strip of bark to sniff for the telltale sour aroma. The orchardists agreed on the classic symptoms of Bacterial Canker.
What can we do? Both orchardists agreed there is no magic bullet, no spray that will protect the trees. This type of bacteria (Pseudomonas syringae) is all around us and is carried by the wind. The orchardists recommended that we focus on growing resilient roots. Remove the dead roots and expose the soil to sunlight as soon and as long as possible. Treat with mustard meal. Shine the light on the bad actors: ring nematodes. These microscopic organisms nibble away at the growing roots and make the small trees vulnerable to the Bacterial Canker in the winter.
How does this happen? Terence explained how winter freezes create cracks in the bark of small trees creating openings for the bacteria to enter. Andy explained the chill factor is essential for the dormant buds to “wake up” in the spring. Warmer winters with less chill factor mean the protective scales around the buds do not lose their inhibitory influence. It is as if the bud scales have a “turn off” signal. Not enough chill means the “turn off” signal does not switch to “turn on.”
The seven large trees in poor condition were a different matter. They started showing signs of decline during the summer even though they were getting drip irrigation. Oak root fungus is the likely bad actor for large trees that endured the drought of 2020-2021 and suboptimal irrigation in the two following years. The prescription is immediate removal of the infected soil and solar radiation for a year at the tree-site to remove the persistent fungus.
For the first time in 124 years, we face the difficult task of removing 92 diseased trees to combat ring nematodes and Oak Root Fungus. But hope is far from lost. Our commitment to stewarding this historic orchard remains as strong as ever. Stay tuned as we harness the power of solar radiation in our fight to restore its health!
Click here to view the Arborist Report pending review by the City’s Development Services Department.
Contributed by Jane Packard, chair of the Orchard Commons Committee
To cleanse the soil, Roots of infected trees were removed.
Trees were replanted at tree sites where tests showed there were no ring nematodes.
