Blue Diamond Almond Facts March-April 2022

experiment, cut leafing out shoots were sprayed with ”ice-nucleating” (the ability to catalyze the formation of ice) Pseudomondas syringe before being subjected to freezing temperatures. Other shoots were also inoculated but not chilled. Damage to leaf clusters were significantly greater in shoots that had been inoculated and chilled, confirming the interaction between ice-nucleating bacteria and freezing temperatures with bacterial blast. Trees growing in sandy soils with high ring nematode populations and low nutrient value, typically flood irrigated with district water, appear to be the most susceptible to bacterial canker. Bacterial canker control usually includes preplant fumigation for ring nematode, proper rootstock selection, proper irrigation and nutrition (especially nitrogen and perhaps calcium and iron), and post plant nematicide treatments (less successful — Movento and VelumOne).

Conversion to drip irrigation systems have in general improved bacterial canker incidence. Roger Duncan, UC Farm Advisor in Stanislaus County, has shown Viking and Lovell rootstocks to be more tolerant than peach-almond hybrids (Hansen, Nickels, and Brights) and Nemaguard. Duncan also cooperated with research that showed copper sprays may also play an important role at reducing bacterial populations. Silicone-based surfactants may help deliver bactericides into previous inaccessible leaf surfaces. There is limited evidence that defoliating leaves in the fall with zinc or urea may improve bacterial canker symptoms. We wonder if freezing temperatures in the fall, before trees were completely dormant, may contribute to early bud infections, because sometimes dormant buds appear to be killed even before bloom. I’m guessing that frost events and rainfall may allow the bacterium to enter the plant early

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