Bacterial spot was only discovered a few years ago in the Central Valley and some growers aren’t familiar with it. Pomology tree crop advisor David Doll says we haven’t seen a big problem in the last few years but a certain type and timing of precipitation can make the issue worse.
Epidemiology of Bacterial Spot
From The Almond Doctor blog: The pathogen is readily isolated from overwintering symptomatic fruit mummies well into the spring season, indicating their role as primary inoculum sources during infection periods. Twig lesions and bud death were not observed in our studies but have been reported on other Prunus spp. In the spring of 2014, wet and warm conditions did not occur until mid- to late March, and fruit symptoms were first observed in mid- April. Infections appear to initiate on developing fruit during or immediately after shuck split under favorable conditions. The bacterial pathogen needs splashing water to spread and wet conditions to infect. On other crops in the eastern United States, high winds during rain generally cause more severe infection periods. Read more from The Almond Doctor.