recently registered such as mefentrifluconazole (Cevya) and premixtures such as difenoconazole-pydiflumetofen (Miravis Duo) that have built-in resistance management mechanisms. Frost can occur, so keep vegetation mowed and avoid working the soil from bloom through the end of March. The UC Almond Production Manual has a chart that displays temperatures at which cold induced damage can occur for different varieties. Freezes can occur through early April, so be prepared to run water if you can. Bacterial blast and canker develop under cold, wet environments. In 2020 there was an increased incidence of blast, especially in northern California almond production areas. Blast symptoms are often confused with brown rot blossom blight. The difference is that blossom blight often has tan to brown fungal sporulation on the dead flower parts. The Almond Alliance of California and Dr. Adaskaveg have requested the renewal of the emergency registration (Section-18) for kasugamycin (Kasumin) for February–April 2022, like the previous two years. A full registration on almond is pending for early 2022. Kasugamycin should be applied before frost events, especially on varieties susceptible to blast such as
Independence, Aldrich, Monterey, and Fritz. Frost or frozen water causes tissue expansion and injury that is subsequently colonized by the ubiquitous epiphytic bacterium Pseudomonas syringae. In California, the pathogen is mostly resistant to copper. Kasugamycin is compatible with fungicides, and tank mixtures can be used during bloom and petal fall if cold wet weather is forecasted to minimize application costs. Integrated strategies are best for managing diseases like bacterial blast, thus, frost protection irrigation and the use of kasugamycin should be highly effective. Good Luck and Stay Safe!
Brent Holtz, Ph.D., Orchard Systems Advisor, University of California Cooperative Extension in San Joaquin County baholtz@ucanr.edu
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