Blue Diamond Almond Facts March-April 2022



Orchard Care This Spring I saw bacterial blast-like symptoms on Independence blossoms in March, as well as bacterial canker-like symptoms on trees. They may have had an incompatibility issue between the Independence scion and Krymsk rootstock. Bacterial canker, blossom, and bud blast are all caused by a plant-pathogenic bacterium called Pseudomondas syringae pv. syringae that is usually found living on the surface of healthy plants. Pseudomondas syringae lives most of the time as an “omnipresent epiphyte,” always present on the surface of plants, living happily, just waiting for certain environmental conditions (cold and wet) that allow it to enter the plant, multiply, and build to high enough populations within the tree to trigger a disease (bacterial blast or canker). Relatively little is known about blossom and leaf bacterial blast, but we do know that cold wet weather can be important predisposing factors that can worsen the disease. The picture of “blasted” blossoms are from trees growing in sandy soils in an orchard near Manteca. We had some cold temperatures in late February early March that could have created small wounds that allowed the bacteria to enter leaves and blossoms. Bacterial blast is usually more severe in the lower canopy of the tree and in the lower part of an orchard. Blast is usually more severe on earlier blooming varieties, but that may be because earlier blooming varieties tend to be in bloom when temperatures are cooler. Aldrich and Fritz are typically less affected than Nonpareil, Independence, or Carmel. Bacterial blossom blast has been significantly reduced in trials where trees were protected against frost by running water or wind machines. Harley English, a UC Davis professor in the 1980s, conducted a series of experiments on bacterial blossom blast. Cut blossoming shoots of almond that were subjected to 24.8°F (-4°C) for two hours were significantly more susceptible to blast than shoots that were not subjected to the two-hour frost treatment. In another

Bacterial Blast

Bacterial Canker

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